REPORT NO. 312 Dynamic Testing of Ground Support Systems

REPORT NO. 312

Dynamic Testing of Ground Support Systems

Results of research carried out as MRIWA Project M417

at the WA School of Mines, Curtin University by

E Villaescusa, A G Thompson and J R Player August 2015

Distributed by: MRIWA Mineral House 100 Plain Street Perth WA 6000 to which all enquiries should be addressed

© Crown Copyright reserved ISBN 192098173X

EXECUTIVE SUMMARY This report is the culmination of research investigations commenced in July 2002. This document provides an overview of the three MERIWA Projects M349 (Phase I), M349A (Phase II) and M417 (Phase III) and their achievements. First, in Section 1, the objectives of all three projects will be presented. Then details will be provided for the basic terminology that will b e used throughout the report and the types of loading to which ground support is subjected and how it responds. This information is then put into the context of how a testing facility is used to simulate these loadings and to measure, quantify and compare the performances of various ground support systems. Section 2 provides detailed descriptions of the significant modifications and enhancements made during Phase III and the current attributes of the test facility. Section 3 describes testing programs of samples of various reinforcement systems. Section 4 describes the configurations and results for mesh support systems that were subjected to dynamic testing. Section 5 describes the configurations and results for shotcrete support systems that were subjected to dynamic testing. Section 6 describes the configurations and results for combined reinforcement and mesh panels that were subjected to dynamic testing. Section 7 describes a new methodology for ground support design in high stress environments susceptible to violent rock mass failures. Section 8 summarises the achievements and outcomes from the three phases of the project that commenced in June 2002 and were completed in July 2015. Finally, a list of references is provided at the end of the report.

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TABLE OF CONTENTS 1 1.1 1.2 1.3

BACKGROUND INFORMATION .....................................................................................................1 INTRODUCTION...................................................................................................................................1 PROJECT OBJECTIVES, SCOPE OF WORK AND TASKS ...............................................................2 GROUND SUPPORT SCHEMES AND TERMINOLOGY ..................................................................2 1.3.1 Load Transfer Concept for Reinforcement and Support Systems ................................................3 1.3.2 Reinforcement System Load Transfer ...............................................................................4 1.4 ROCK MASS LOADINGS ....................................................................................................................6 1.5 WASM DYNAMIC TEST FACILITY AT THE COMPLETION OF PHASE 2. ..................................9 2 WASM DYNAMIC TEST FACILITY – UPDATE AND CURRENT STATUS ........................... 11 2.1 INTRODUCTION.................................................................................................................................11 2.2 INFRASTRUCTURE ...........................................................................................................................11 2.2.1 Building ...........................................................................................................................11 2.2.2 Storage .............................................................................................................................11 2.3 TESTING EQUIPMENT ......................................................................................................................11 2.3.1 Gantry Crane and Lift Motor ...........................................................................................11 2.3.2 Release Mechanism .........................................................................................................11 2.3.3 Drop Beams .....................................................................................................................11 2.3.4 Sample Preparation Jacks ................................................................................................12 2.3.5 Buffers .............................................................................................................................12 2.3.6 Simulated Rock Loading..................................................................................................12 2.3.7 Weighing of Components ................................................................................................12 2.3.8 Simulated Borehole Preparation ......................................................................................12 2.3.9 Shotcrete Sample Preparation ..........................................................................................12 2.4 MONITORING SYSTEM ....................................................................................................................13 2.4.1 Computer and Data Acquisition Software .......................................................................13 2.4.2 High Speed Video Camera ...............................................................................................13 2.4.3 Instrumentation ................................................................................................................14 2.4.4 Data Storage and Archiving .............................................................................................14 2.5 THEORETICAL DEVELOPMENTS ...................................................................................................14 2.5.1 Force Transfer and Displacements ...................................................................................14 2.5.2 Reinforcement ..................................................................................................................14 2.5.3 Mesh ................................................................................................................................16 2.5.4 Shotcrete ..........................................................................................................................16 2.5.5 Combined Systems...........................................................................................................16 2.5.6 Summary ..........................................................................................................................18 2.6 DYNAMIC TEST DATA ANALYSIS SOFTWARE ..........................................................................19 2.6.1 Dynamic Utility ...............................................................................................................19 2.7 DATA ANALYSIS PROCEDURE ......................................................................................................22 2.7.1 Data Visualisation ............................................................................................................22 2.7.2 Data Filtering ...................................................................................................................23 2.7.3 Saving of Filtered Data ....................................................................................................23 2.7.4 Re-Filtering Data .............................................................................................................24 2.7.5 Time Synchronisation and Other Adjustments of Data....................................................24 2.7.6 Engineering Analysis .......................................................................................................24 2.8 TEST REPORTING ..............................................................................................................................27 2.8.1 Laboratory Recording Sheet ............................................................................................27 2.8.2 System Performance ........................................................................................................27 2.9 TRAINING ...........................................................................................................................................27 2.10 SUMMARY OF THE WASM TEST FACILITY ................................................................................27 2.10.1 Features of the Facility.....................................................................................................27 2.10.2 Limitations of the Facility ................................................................................................28 2.10.3 Concluding Remarks ........................................................................................................28

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TABLE OF CONTENTS 3 TESTING OF REINFORCEMENT SYSTEMS .............................................................................. 29 3.1 INTRODUCTION.................................................................................................................................29 3.2 SIMULATED BOREHOLES ...............................................................................................................29 3.2.1 Pipe Radial Stiffness ..................................................................................................................29 3.2.2 Simulated Rock Material Selection ............................................................................................29 3.2.3 Preparation of Simulated Boreholes ...........................................................................................30 3.2.4 Reinforcement Systems..............................................................................................................31 3.3 TESTING PROGRAMS .......................................................................................................................32 3.3.1 Newcrest Program......................................................................................................................32 3.3.2 Cable Bolt Testing .....................................................................................................................36 3.3.3 CODELCO Program 1 ...............................................................................................................37 3.3.4 BHP Billiton Program ................................................................................................................66 3.3.5 DSI Posimix Bolts......................................................................................................................69 3.4 REINFORCEMENT DATABASE .......................................................................................................72 4 4.1 4.2 4.3

TESTING OF MESH SUPPORT SYSTEMS ................................................................................... 75 INTRODUCTION.................................................................................................................................75 WOVEN WIRE STEEL WIRE MESH TESTING ...............................................................................75 Static Mesh Testing ...............................................................................................................................75 4.3.1 Introduction ................................................................................................................................75 4.3.2 WASM Static Facility ................................................................................................................76 4.3.3 Description of the failure modes on the various mesh types ......................................................77 4.3.4 Static Test Results Summary .....................................................................................................79 4.4 DYNAMIC TESTING ..........................................................................................................................82 4.4.1 Mesh Testing Configuration ......................................................................................................82 4.4.2 Test Summary ............................................................................................................................83 4.5 MESH DATABASES ...........................................................................................................................84 4.5.1 Dynamic Charts .........................................................................................................................88 4.5.2 Interpretation of WASM Mesh Testing Databases ....................................................................88 5 COMBINED REINFORCEMENT AND MESH SYSTEMS .......................................................... 89 5.1 INTRODUCTION.................................................................................................................................89 5.2 SAMPLE PREPARATION...................................................................................................................89 5.2.1 Grouting of Simulated Boreholes ..............................................................................................89 5.2.2 Attachment of Mesh on to the Mesh Frame ...............................................................................91 5.2.3 Placement of the Simulated Borehole onto the Drop Beam and to the Loading Mass ...............92 5.2.4 Attachment of Mesh Frame on to the Drop Beam .....................................................................93 5.2.5 Installation of Surface Hardware and the Collar Load Cell .......................................................95 5.2.6 Installation of the Instrumentation .............................................................................................96 5.2.7 Pre-Test Checks and Measurements ..........................................................................................96 5.3 TYPICAL ANALYSIS PROCEDURE.................................................................................................98 5.3.1 Video Data Analysis ..................................................................................................................99 5.3.2 Sensor Data Analysis ...............................................................................................................105 5.3.3 Dissection Analysis. .................................................................................................................116 5.4 TEST RESULTS .................................................................................................................................118 5.4.1 Combined Test Specifications .................................................................................................118 5.4.2 Summary of Results and Comments ........................................................................................120 5.4.3 The Dynamic Force – Displacement Responses ......................................................................122 5.4.4 Energy Dissipated by the Reinforcement and Support Systems ..............................................126

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TABLE OF CONTENTS 6 6.1 6.2 6.3 6.4 6.5

METHODOLOGY FOR GROUND SUPPORT DESIGN ............................................................ 129 INTRODUCTION...............................................................................................................................129 STRESS DRIVEN FAILURES...........................................................................................................129 ENERGY RELEASE ..........................................................................................................................131 ROCK MASS DEMAND ...................................................................................................................132 GROUND SUPPORT DESIGN..........................................................................................................133

7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

SUMMARY OF OUTCOMES AND CONCLUDING REMARKS ............................................. 137 SUMMARY OF OUTCOMES FROM RESEARCH INVESTIGATIONS .......................................137 WASM DYNAMIC TEST FACILITY ...............................................................................................137 REINFORCEMENT SYSTEM TESTING .........................................................................................138 MESH TESTING ................................................................................................................................138 COMBINED REINFORCEMENT AND MESH TESTING ..............................................................138 DESIGN METHODOLOGY FOR GROUND SUPPORT .................................................................139 RESEARCH STAFF AND STUDENTS ............................................................................................139 TECHNOLOGY TRANSFER ............................................................................................................139 7.8.1 Published Papers ............................................................................................................139 7.8.2 Student Theses ...............................................................................................................141 7.8.3 MERIWA Reports .........................................................................................................141 7.8.4 Seminars/Workshops/Courses .......................................................................................142 7.8.5 Progress Reports ............................................................................................................142 7.8.6 Sponsor Collaboration ...................................................................................................142 7.8.7 Sponsors’ Meetings ........................................................................................................142 7.9 ACKNOWLEDGEMENTS ................................................................................................................143 7.10 CONCLUDING REMARKS ..............................................................................................................143 REFERENCES .......................................................................................................................................... 145

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LIST OF FIGURES Figure 1.1: Load transfer from surface support to surrounding reinforcement systems. ........................................ 3 Figure 1.2: Load transfer between surface support and the surrounding rock surface. ........................................... 4 Figure 1.3: Reinforcement load transfer from unstable rock to stable rock ............................................................ 4 Figure 1.4: The components of a reinforcement system ......................................................................................... 5 Figure 1.5: Schematic showing the different element force distributions within each of the three classes of reinforcement systems. .......................................................................................................................................... 6 Figure 1.6: Schematic representation of rock failure loading surface support between reinforcement................... 7 Figure 1.7: Schematic representation of rock failure loading both surface support and reinforcement. ................. 8 Figure 1.8: WASM Dynamic Test Facility for testing of reinforcement. ............................................................. 10 Figure 2.1: New and old frames used for spraying and transport of shotcrete panels........................................... 13 Figure 2.2: Free-body diagram showing load transfer mechanisms within a reinforcement system .................... 15 Figure 2.3: Free body force diagram for dynamic testing of combined reinforcement and mesh panels. ............ 17 Figure 2.4: Free body force diagram for dynamic testing of combined reinforcement and rock substrate/shotcrete panels ................................................................................................................................................................... 18 Figure 2.5: User interface of the new Dynamic Utility populated with configuration data for a combined reinforcement and mesh test. ............................................................................................................................... 20 Figure 2.6: Instrumentation configuration data. ................................................................................................... 21 Figure 2.7: User interface for analysis of dynamic data. ...................................................................................... 22 Figure 2.8: Typical accelerometer signal without processing. .............................................................................. 23 Figure 2.9: Accelerometer response after filtering. .............................................................................................. 24 Figure 2.10: Interface used to select channels for analysis for a reinforcement test ............................................. 26 Figure 3.1: Details of a) sample preparation and b) following cement grouting. ................................................. 30 Figure 3.2: Heavy pipes ready for cement grouting.............................................................................................. 31 Figure 3.3: Details of DSI Posimix and threaded rebar to be tested at WASM .................................................... 31 Figure 3.4: Details of some of the CODELCO bolts tested at WASM. ................................................................ 32 Figure 3.5: Fully encapsulated resin grouted bar failing by rupture. .................................................................... 33 Figure 3.6: Fully encapsulated resin grouted bar slipping significantly. .............................................................. 33 Figure 3.7: Summary of results for Newcrest testing program ............................................................................. 35 Figure 3.8: Cross sectional view of the Roofex bolt (Neugebauer, 2008). ........................................................... 38 Figure 3.9: Catastrophic failure of the Roofex bolt. ............................................................................................. 39 Figure 3.10: Roofex bolt mechanism of energy absorption and resulting failure ................................................. 39 Figure 3.11: Components and mechanism of Yield-Lok reinforcement system (After Wu and Oldsen, 2010). .. 40 Figure 3.12: Stability achieved (after large displacement) with the Yield-Lok bolt. ............................................ 41 Figure 3.13: Longitudinal section view of Yield-Lok bolt showing the void left after bolt plowing through the confined polymer. ................................................................................................................................................ 41 Figure 3.14: Details of cement grouted D-Bolt and dimensions (mm) ................................................................. 42 Figure 3.15: Stability achieved (after moderate displacement) with the D-Bolt. .................................................. 42

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LIST OF FIGURES Figure 3.16: Longitudinal section view of D-bolt showing no anchor movement. ............................................... 43 Figure 3.17: Components of the Dynatork reinforcement system ........................................................................ 43 Figure 3.18: Inspection following dynamic testing of a Dynatork bolt. ............................................................... 44 Figure 3.19: Post-test inspections for a 17mm diameter Dynatork bolt. ............................................................... 44 Figure 3.20: Post-test inspection following dynamic testing of a Dynatork bolt. ................................................. 45 Figure 3.21: Details of Durabar reinforcement system ......................................................................................... 46 Figure 3.22: Post-test inspection following dynamic testing of a Durabar bolt. ................................................... 46 Figure 3.23: Anchor point inspection following dynamic testing of a Durabar bolt............................................. 47 Figure 3.24. Detailed view of the Garford bolt components (Lachenicht et al, 2008) .......................................... 48 Figure 3.25: Catastrophic failure of the Garford bolt. .......................................................................................... 49 Figure 3.26: Rupture surface of the end-stop mechanism for a Garford bolt........................................................ 49 Figure 3.27: Excessive displacement and rupture of the end-stop mechanism for a Garford bolt. ....................... 50 Figure 3.28: Post-test inspection following dynamic testing of an unstable Grade 40, 22mm threaded bar. ........ 51 Figure 3.29: Post-test inspection following dynamic testing of a stable Grade 40, 22mm threaded bar............... 52 Figure 3.30: Post-test inspection following dynamic testing of a stable (with plate damage) Grade 40, 25mm threaded bar. ........................................................................................................................................................ 53 Figure 3.31: Bolt-grout interaction inspection following dynamic testing of a Grade 40, 25mm threaded bar .... 54 Figure 3.32: Post-test inspection following dynamic testing of a stable Grade 40, 25mm threaded bar............... 55 Figure 3.33: Bolt-grout interaction inspection following dynamic testing of a Grade 40, 25mm threaded bar .... 56 Figure 3.34: Post-test inspection following dynamic testing of a stable (plate damage) Grade 40, 25mm threaded bar ........................................................................................................................................................................ 57 Figure 3.35: Post-test inspection following dynamic testing of a stable Grade 60, 22mm threaded bar............... 58 Figure 3.36: Grade 60, 22mm threaded bar tested twice (repetitive dynamic loading). ............................. 59 Figure 3.37: Bolt-grout interaction inspection following dynamic testing of a Grade 60, 22mm threaded bar .... 59 Figure 3.38: Bolt-grout interaction inspection following dynamic testing of a Grade 60, 22mm threaded bar .... 60 Figure 3.39: Post-test inspection following a high energy impact testing of a Grade 60, 22mm threaded bar ..... 61 Figure 3.40: Bolt-grout interaction inspection following a high energy impact testing of a Grade 60, 22mm threaded bar. ........................................................................................................................................................ 62 Figure 3.41: Bolt-grout interaction inspection following a high energy impact testing of a Grade 60, 22mm threaded bar. ........................................................................................................................................................ 63 Figure 3.42: A comparison of energy dissipation for different reinforcement systems tested for CODELCO..... 65 Figure 3.43: Mechanical installation of full scale rock bolts using resin encapsulation. ...................................... 66 Figure 3.44: Dynamic Load-Displacement results for resin encapsulated D-Bolts. ............................................. 67 Figure 3.45: Different load transfer effectiveness for a similar rock bolt. ............................................................ 68 Figure 3.46: Example of different resin mixing results for D-Bolts. .................................................................... 68 Figure 3.47: Example of poor resin mixing due to enlargement of simulated hole diameter. .............................. 69 Figure 3.48: Cross sectional view of a fully encapsulated (decoupled) Posimix bolt. .......................................... 69

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LIST OF FIGURES Figure 3.49: Dynamic testing of Posimix thread-nut geometry. ........................................................................... 70 Figure 3.50: Dynamic load-displacement response for a number of Posimix bolts. ............................................. 71 Figure 3.51: WASM Reinforcement Capacity database (Player, 2012). ............................................................. 73 Figure 4.1: WASM Static Test Facility ................................................................................................................ 76 Figure 4.2: Welded sheet mesh wire failure mechanism; left to right, tensile failure, weld failure, failure through heat affected zone ................................................................................................................................................ 77 Figure 4.3: Typical failure mode of the tests at the edge of the loading plate (hardened steel) ............................. 78 Figure 4.4: Force-Displacement chart from the static test results from Table 4.2................................................. 80 Figure 4.5: Force – displacement graph for all the static test results from Table 4.2............................................. 81 Figure 4.6: Calculated energy – displacement graph for all the static test results from Table 4.2. ....................... 81 Figure 4.7: Mesh sample and loading configuration immediately before dynamic testing. ................................. 82 Figure 4.8: WASM dynamic test results, Force-Displacement capacity............................................................... 83 Figure 4.9: WASM dynamic test results, Energy-Displacement capacity ............................................................ 84 Figure 4.10: Summary of static rupture force and energy-displacement for galvanised welded wire mesh with different wire diameters. ...................................................................................................................................... 85 Figure 4.11: Summary of static rupture force and energy versus displacement for welded wire mesh as a function of degree of corrosion. .......................................................................................................................... 86 Figure 4.12: Summary for static rupture peak force and peak energy versus displacement of woven wire mesh .... 87 Figure 4.13: Dynamic Rupture Force-Displacement summary. ........................................................................... 88 Figure 5.1: Fixing of centralisers on bars prior to grouting. ................................................................................. 90 Figure 5.2: The toe grout connection. ................................................................................................................... 90 Figure 5.3: The grouting process. ......................................................................................................................... 91 Figure 5.4: Fixing of the mesh on to the frame ..................................................................................................... 92 Figure 5.5: Setting up the reinforcement system .................................................................................................. 93 Figure 5.6: Fixing of the beam on to the mesh frame ........................................................................................... 94 Figure 5.7: Lowering down the system onto the buffers. ..................................................................................... 95 Figure 5.8: Details of configuration with collar load cell. .................................................................................... 96 Figure 5.9: Pre mesh deflection measurements. ................................................................................................... 97 Figure 5.10: Mesh deformation details of test #195. ............................................................................................ 98 Figure 5.11: Video analysis process. .................................................................................................................... 99 Figure 5.12: Selecting the time window (windowing). ....................................................................................... 100 Figure 5.13: Zooming of windowed data. ........................................................................................................... 100 Figure 5.14: Calibration for the drop plane. ....................................................................................................... 101 Figure 5.15: Progressive ProAnalyst tracks of the targets. ................................................................................. 102 Figure 5.16: The interface of the WASM in-house pre-processing utility .......................................................... 103 Figure 5.17: Raw video data response ................................................................................................................ 104 Figure 5.18: Smoothed video data file. ............................................................................................................... 104

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LIST OF FIGURES Figure 5.19: Sensor data analysis process .......................................................................................................... 105 Figure 5.20: Raw data recorded for sample #195. .............................................................................................. 106 Figure 5.21: Windowed raw data of the loading mass accelerometer (ac02) for sample #195. .......................... 107 Figure 5.22: Frequency analysis for the loading mass accelerometer (ac02) for sample #195. .......................... 107 Figure 5.23: 100Hz filter for loading mass accelerometer for sample #195. ...................................................... 108 Figure 5.24: Filtered accelerometer data of sample #195. .................................................................................. 109 Figure 5.25: The left buffer potentiometer data for the sample #195. ................................................................ 110 Figure 5.26: Filtered left buffer potentiometer data using Butterworth filter. .................................................... 110 Figure 5.27: Potentiometers and load cells filtered data with use of the Butterworth filter. ............................... 111 Figure 5.28: Filtered sensor data before time synchronisation. .......................................................................... 112 Figure 5.29: Adjusting of filtered data using the WASM in-house software. ..................................................... 112 Figure 5.30: Adjusted sensor data file. ............................................................................................................... 113 Figure 5.31: Support Scheme Force – Time response of sample #195. .............................................................. 114 Figure 5.32: Support Scheme Force – Displacement Response of sample #195. ............................................... 114 Figure 5.33: The energy summary graph of sample #195. ................................................................................. 115 Figure 5.34: Collar section of sample #195. ....................................................................................................... 116 Figure 5.35: Toe section of sample #195. ........................................................................................................... 116 Figure 5.36: Both the toe and the collar sections ................................................................................................ 117 Figure 5.37: (L) Pre-test surface hardware, (R) Post-test surface hardware of sample #195 .............................. 117 Figure 5.38: Dynamic force-time response of combined systems. ..................................................................... 123 Figure 5.39: Dynamic Force – Time response of fully bonded threaded bars (Program 1). ............................... 124 Figure 5.40: Dynamic Force – Time response of 1m decoupled threaded bars (Program 1) .............................. 125 Figure 5.41: Dynamic Force – Time response of 1.4m decoupled DSI Posimix (Program 2). ........................... 125 Figure 5.42: Design of combined scheme under dynamic loading. .................................................................... 128 Figure 6.1: Violent, stress driven rock mass failure. .......................................................................................... 130 Figure 6.2: Modelled damage zones for rock reinforcement design (Wiles et al, 2004). ................................... 131 Figure 6.3: Oval excavation shape, suitable for re-distribution of large induced stress...................................... 131 Figure 6.4: Observed damage near the boundary of an excavation in hard rock under very high stress. ........... 133 Figure 6.5: Design of rock reinforcement under dynamic loading (data from Player, 2012). ............................ 135

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LIST OF TABLES Table 3:1: Summary of Newcrest testing program ............................................................................................... 34 Table 3.2: Summary of results from dynamic testing of cement grouted plain single strand cables. ................... 36 Table 3.3: Summary of dynamic properties of cement grouted bolts (CODELCO El Teniente). ........................ 64 Table 3.4: Energy dissipation from thread-nut interaction - debonded Posimix bolts. ......................................... 70 Table 3.5: Energy dissipation – Posimix bolts...................................................................................................... 72 Table 4.1: Main characteristics of TECCO G80/4, DELTAX G80/3 and MINAX M85/2.7 mesh ........................ 75 Table 4.2: Results from the static tests .................................................................................................................. 79 Table 4.3: Summary of executed dynamic tests with various mesh types ............................................................. 83 Table 5.1: Sample specifications – Program 1.................................................................................................... 118 Table 5.2: Sample specifications – Program 2.................................................................................................... 118 Table 5.3: Test sample configurations. ............................................................................................................... 119 Table 5.4: Summary of Program 1...................................................................................................................... 120 Table 5.5: Summary of Program 2...................................................................................................................... 121 Table 5.6: Summary of support system responses. ............................................................................................. 122 Table 5.7: Energy dissipated by the combined schemes. .................................................................................... 126 Table 5.8: Typical Rock Mass Demand for Ground Support Design. ................................................................ 127 Table 6.1: Typical rock mass demand for ground support design (modified after Thompson et al. 2012) ........ 134 Table 7.1: Summary of tests performed in M417. ............................................................................................. 138

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1

BACKGROUND INFORMATION

1.1

INTRODUCTION

This report assumes that the reader is familiar with the objectives of the overall dynamic testing of ground support project and has read the Final Reports that were prepared at the completion of Phase I (M349) and Phase II (M349A). It is also worth noting that the WASM Dynamic Test Facility and its researchers, based on work completed in Phase 1, received a Special Commendation for Research and Development at the 2005 Western Australian Engineering Excellence Awards. Since that time, the WASM Dynamic Test Facility has undergone continuous improvements in its capabilities to test different reinforcement and surface support systems and their combinations. The computer software developed in-house for test data analysis has also undergone continuous development to improve its efficiency and reliability. This report provides:  A restatement of the primary objectives and the scope of work and tasks that evolved during this Phase III project.  A background to ground support schemes and their mechanisms of response to rock mass and laboratory loadings.  A review of the status of the WASM Dynamic Test Facility at the completion of Phase II.  An account of the design modifications to the WASM Dynamic Test Facility and their implementation.  Documentation of the modifications to the instrumentation and monitoring system.  The development of software to analyse the results obtained from dynamic tests of surface support systems and combined reinforcement and support systems.  Detailed results obtained from the dynamic testing of reinforcement systems.  Comparisons and evaluations of the responses of different reinforcement systems.  Details of programs of testing of surface support systems.  Comparisons and evaluations of the responses of different support systems.  Details of dynamic testing of combined reinforcement and surface support schemes.  A description of a new methodology for ground support design based on the extensive database of testing results.

1: Background

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1.2

PROJECT OBJECTIVES, SCOPE OF WORK AND TASKS

Three main objectives were identified in the original research project proposal, namely:  To establish a permanent dynamic testing facility in Kalgoorlie, WA.  To establish databases of measured dynamic responses for different types of reinforcement and support systems.  To establish guidelines for expected energy absorption of various types of reinforcement and support systems. The ultimate aim was:  To establish criteria for selection of ground support schemes based on rock mass characteristics and expected energies associated with seismic loadings. It was identified prior to the commencement of the project that these overall objectives would need to be divided into at least three phases. The Phase One objectives became:  To design, build and commission the test facility and instrumentation and to test rock reinforcement systems comprising various elements, internal fixtures, external fixtures and face restraint. The Phase Two objectives became:  To undertake any modifications required to the test equipment and instrumentation and perform tests on surface support systems as currently used, or could potentially be used, by the Western Australian mines. The Phase Three objectives became:  To undertake any modifications required to the test equipment and instrumentation and perform tests on combined surface support and reinforcement schemes as currently used, or could potentially be used, by the sponsor mines.

1.3

GROUND SUPPORT SCHEMES AND TERMINOLOGY

Ground support schemes consist of rock reinforcement systems and surface support systems. A rock reinforcement system consists of a single element fixed within a bore hole, drilled into the rock mass, and an exterior face plate with external fixture. A pattern of reinforcement systems is often used to support large blocks and prevent large scale ground deterioration. The type of element, and the spacing of each system, depends on the materials available locally and the prevailing geological conditions, namely, the geometry of the potentially unstable blocks and the loading conditions.

2

1: Background

Surface support systems are used between reinforcement systems to prevent smaller scale instability and unravelling of the rock mass. The surface support systems are restrained by the face plates used with the rock reinforcement systems to form an integrated ground support scheme. Surface support systems include simple rolls or sheets of steel wire mesh, or sprayed layers such as shotcrete and membranes that harden and apply a reactive force to the rock face. 1.3.1

Load Transfer Concept for Reinforcement and Support Systems

Examples of ground support schemes comprising reinforcement systems and/or surface support systems are shown schematically in Figure 1.1 and Figure 1.2. The load transfer concept for reinforcement and support systems involves considering the response of these systems to rock movement.

Unstable Block

Restraint

Mesh, Strap or Sprayed Layer or Coating

Restraint

Figure 1.1: Load transfer from surface support to surrounding reinforcement systems.

1: Background

3

Unstable Block

Adhesion Required

Adhesion Required

Sprayed Layer or Coating

Figure 1.2: Load transfer between surface support and the surrounding rock surface. In the case of support, it can often be assumed that the support is locally slab like and transfers force to points of restraint such as rock bolts or cable bolts (Figure 1.1) or zones of restraint provided by adhesion between the support system and the rock surface (Figure 1.2). In practice, shotcrete is usually curved and this affects its response to rock mass loading. The effects of rock surface curvature and their interaction with rock have been discussed in detail by Windsor (2012), Thompson et al. (2012) and Windsor and Roth (2013). 1.3.2

Reinforcement System Load Transfer

In the case of a reinforcement system, it is assumed that the reinforcement transfers force across a distinct interface or zone between unstable and stable rock as shown in Figure 1.3.

Excavation

Unstable Surface Region

Stable Interior Region

Figure 1.3: Reinforcement load transfer from unstable rock to stable rock.

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1: Background

A reinforcement system can be considered to consist of 4 components as shown in Figure 1.4, namely: 0.

The rock.

1.

The element.

2.

The internal fixture.

3.

The external fixture.

Figure 1.4: The components of a reinforcement system. The response of the reinforcement system to rock loading involves several modes of load transfer between the various components. The modes of load transfer between the element and rock lead to a simple classification system described by Windsor and Thompson (1996). This classification system resulted in only three basic classes of reinforcement systems, namely: 1.

Continuously Mechanically Coupled (CMC) Systems.

2.

Continuously Frictionally Coupled (CFC) Systems.

3.

Discretely Mechanically or Frictionally Coupled (DMFC) Systems.

It can be readily demonstrated that all commercial reinforcement systems can be considered to fit within one of these three classes. The load transfer and distribution of force for reinforcement systems within each of the three classes differ greatly in their responses and abilities to sustain dynamic loading. Figure 1.5 shows conceptually the expected force distributions within each class. These conceptual force distributions can be used as the basis for analysis and to identify where to instrument reinforcement systems in both the field and in the laboratory (Thompson and Windsor, 1993). The same force distributions also suggest which commercially available configurations are most suitable for application to rock which may be susceptible to violent rock failure and dynamic loading.

1: Background

5

Stable Region

Unstable Region

Movement Vector

CMC

CFC

DMFC

Figure 1.5: Schematic showing the different element force distributions within each of the three classes of reinforcement systems.

1.4

ROCK MASS LOADINGS

In order to properly design testing facilities and associated procedures it is first necessary to understand the in situ interaction between ground support schemes and the rock mass. An important aspect of the ground support scheme response is the amount of rock mass deformation and the rate at which it occurs. Should there be an ejection of rock, the reinforcement system should dissipate the momentum from the block of rock. The momentum is equal to the mass of the block multiplied by its initial ejection velocity. The momentum of the ejected rock is reduced by transfer of load to the stable rock. The load in the reinforcement causes a deceleration and reduction in the block velocity. To simulate this, the test must be of double embedment configuration with collar and toe anchor lengths and a collar geometry that allows tension to be applied to the surface restraint. This generates the correct load transfer to the reinforcement system and allows for failure to occur at whichever is the weakest

6

1: Background

location: the surface hardware connection to the reinforcement element, the reinforcement element at the simulated discontinuity, or decoupling from within the anchor embedment length. It is also possible that a volume of intact rock may fail violently, immediately adjacent to the surface support as shown schematically in Figure 1.6 and Figure 1.7. That is, failure may occur between reinforcement systems or it may be in the volume of rock surrounding a borehole in which reinforcement has been installed. In the former case, the support is required to transfer the dynamic load through the surface support into the reinforcement through the external fixture. In the latter case, the support and reinforcement respond simultaneously and combine to attempt to sustain the dynamic loading. In the former case, it is possible for the surface support to fail and not transfer load to the reinforcement system. This is often observed where rock simply pushes through mesh, particularly at the locations of overlaps at edges of sheets. In the latter case, the proportion of load and energy absorbed by the reinforcement and surface support will be complex and related to the relative stiffness of response. In theory, it would be possible for the reinforcement system to fail, either internally or at the collar, and the surface support to transfer load to adjacent reinforcement systems in the ground support scheme. The WASM Dynamic Test Facility was developed with both mechanisms in mind; that is, a panel of surface support system restrained only at the edges to simulate a continuous sheet or a panel of surface support system restrained both at the edges with a single reinforcement system in the centre of the panel.

Mesh or Shotcrete

Failed Volume of Rock

Figure 1.6: Schematic representation of rock failure loading surface support between reinforcement.

1: Background

7

Failed Volume of Rock

Mesh or Shotcrete

Figure 1.7: Schematic representation of rock failure loading both surface support and reinforcement. In both cases of initiated dynamic loading, a susceptible excavation may involve a detachment process in which a single block or fragments of rock may attempt to eject from the surrounding rock mass into the excavation and load the ground support. This ground support loading is unlikely to be instantaneous, but rather will take a finite time that will for a remote event be related to the seismic wave velocity, amplitude, the acceleration pulse of the dominant frequency and fracture velocity within the rock mass. For a local event, the excitation will be a “pulse” of loading that will result in a mass (M) of rock moving at a particular velocity (v); that is, the failure volume will have a change in momentum that is related to a force (Ft) acting over a short time (t) as suggested by the following impulse equation:

Mv Ft dt

Eq. 1.1

With these models of ground support loading, it is clear that prior to the seismic event, the rock mass and ground support are stationary. After the event, the rock mass is accelerated to a certain velocity in a short, but finite, time. Hence, in a test facility, it is not appropriate to apply the load instantaneously, but rather it should be applied quickly and the rate of application should be measurable and similar to that which is considered to cause damage to underground mine ground support. It is also not appropriate to apply the load simply to the external fixture at the collar of the reinforcement system. At the WASM Dynamic Test Facility loading is provided by the relative velocity between the loading mass and the drop beam, as the momentum of the loading mass is transferred through the reinforcement system and support systems to the drop beam (Thompson et al. 2004). The reinforcement system will yield, slide or break in the process of dissipating the dynamic load. The process will depend on the design and material properties of the reinforcement system, the encapsulation medium and the interaction with the borehole.

8

1: Background

This is best done by applying the input energy via impact by dropping a modelled rock mass and reinforcing system, and the rock mass that remains afterwards onto an engineered impact surface, by dropping the test assembly onto the buffers. The energy dissipation into the impact surface must be measurable and reported with all other parameters from the test. The most appropriate impact surfaces selected are railway buffers used to dissipate the momentum of railway carriages as they are shunted together or into their end stops.

1.5

WASM DYNAMIC TEST FACILITY AT THE COMPLETION OF PHASE II

The WASM Dynamic Test Facility is shown set up for a reinforcement system dynamic test in Figure 1.8. At the completion of Phase II (MERIWA Project M349), the status of the WASM Dynamic Test Facility could be summarised as follows: 

The infrastructure for the facility was successfully constructed.



The instrumentation, monitoring and data storage system were implemented.



Software was developed to analyse the large amounts of data.



The concept of momentum transfer was proven to be capable of providing sufficient energy in a single test to rupture reinforcement systems with force capacities in excess of about 300kN and energy absorption capacities in excess of approximately 40kJ.



The facility was capable of testing panels of mesh and shotcrete and analysing the results.

In the following Section 2 of the final report for MRIWA Project M417, the enhancements made to the facility will be described together with the current status of the facility with respect to dynamic testing of ground support systems, in particular the testing of mesh and shotcrete support systems and combinations of reinforcement with mesh panels.

1: Background

9

Figure 1.8: WASM Dynamic Test Facility for testing of reinforcement.

10

1: Background

2

WASM DYNAMIC TEST FACILITY – UPDATE AND CURRENT STATUS

2.1

INTRODUCTION

The WASM Dynamic Test Facility established on the KCGM lease in Kalgoorlie has been fully described in the final reports of MERIWA Projects M349 and M349A. In this section for the final report for MRIWA Project M417 it is only intended to describe the enhancements made to the facility. The enhancements will be presented in terms of: 

Infrastructure – essentially maintenance and minor improvement



Testing equipment – modifications to existing equipment and manufacture of new equipment



Instrumentation and monitoring system



Theoretical developments



Data analysis software

2.2

INFRASTRUCTURE

A number of changes were made to the WASM Dynamic Test Facility infrastructure to improve efficiency, general working conditions, materials handling and safety. 2.2.1

Building

Minor maintenance only was required for the building. 2.2.2

Storage

Additional covered storage areas were constructed.

2.3 2.3.1

TESTING EQUIPMENT Gantry Crane and Lift Motor

The gantry crane was inspected and tested according to the Australian requirements for safety of lifting equipment. 2.3.2

Release Mechanism

The helicopter release hook was sent away for servicing and then recommissioned. 2.3.3

Drop Beams

At the commencement of project M417, there were two drop beams. One of these was substantially stiffened to enable mesh and shotcrete panel testing for the more recent combined reinforcement

2: WASM Dynamic Test Facility – Update and Current Status

11

and mesh panel testing. However, it was deemed necessary to consider the design and manufacture of a third beam to accommodate larger diameter and longer simulated boreholes as well as to support the frames required for mesh and shotcrete panel testing. Previous design modifications were made in house based on staff expertise. However, for the major upgrade, an external consulting firm was contracted to do the design. From the design specification received, drawings were developed in house to enable the manufacture of the new beam to the tolerances required to slide in the existing guide rails. The new beam was delivered in June 2015. 2.3.4

Sample Preparation Jacks

Four, 2 tonne base jacks to hold the combined mesh and bolt testing geometry were purchased and secured to the concrete slab. 2.3.5

Buffers

The buffers carefully selected for taking the impacts from the drop beam and protection of the concrete foundations have proven to be very resilient to the many impacts since the facility was originally established in 2002. Two additional buffers were purchased to enable testing to continue while two buffers could be sent for routine servicing. 2.3.6

Simulated Rock Loading

A number of new loading mass components were designed and manufactured during the course of this project. 2.3.7

Weighing of Components

A critical aspect of data analysis and calculation of forces from accelerations is the mass of each component. A new measurement device was purchased to enable accurate estimates to be made for the masses of the various testing components. Previously, such equipment was hired on an as required basis. 2.3.8

Simulated Borehole Preparation

A replacement base plate that can be used with the rough simulated boreholes was designed and constructed. A “lattice” of flat plates has been welded to the base plate to provide space for the plate to hit on to the sand filled bags and a rubber base. 2.3.9

Shotcrete Sample Preparation

Six frames were designed and manufactured to enable spraying of shotcrete panels at mine sites and transport back to Kalgoorlie to be placed in curing chambers. The new and old frames are shown in Figure 2.1.

12


Figure 2.1: New and old frames used for spraying and transport of shotcrete panels.

2.4

MONITORING SYSTEM

The objective of the monitoring system and instrumentation is to determine the parameters defining the motion at any time of all components involved in a test. That is, the objective is to be able to measure directly, or derive, the acceleration, velocity and displacement of all components. Knowing the mass of all components, it is then a relatively simple process to calculate the forces, momentum and energy of all the components at any time in a test. The objective is achieved by ensuring that all components are monitored by at least one instrument during a test and that separate sources of data are synchronised in time. During the last 4 years the data acquisition and monitoring system has been upgraded and a number of additional instruments purchased to replace ones that had been damaged or to enable the monitoring of more channels of data during a test. 2.4.1

Computer and Data Acquisition Software

A new computer and the associated ProAnalyst data acquisition control software were purchased and commissioned. A minor change to the structure of the data file created by the new ProAnalyst software required the reinforcement and support data analysis software to be modified to read both the new and old file structures. The new ProAnalyst file structure incorporates a colour code for charts. The same colours are now used for the charts following data filtering and analysis. 2.4.2

High Speed Video Camera

A new camera was purchased and commissioned. The new camera records at 1,000 frames per second compared with the 500 frames per second of the original camera. This means the new video tracking system results in better resolution of displacements leading to better estimates of the values of velocity and acceleration during a test. The new system also allows for tracking of displacements anywhere on the lower surface of a shotcrete (or mesh) layer. Previously, displacements were only able to be tracked on a


13

vertical plane passing through the web of the drop beam. The additional displacement monitoring points may be used to estimate displacement at points other than the centre. The new camera required a new mounting block to be installed. 2.4.3

Instrumentation

A repair of the ground loop of the potentiometer signal was completed. Furthermore, additional laboratory power supply has been acquired. This can be used for the potentiometers while freeing up a power supply for other items such as LED lights. Additional lights could be useful and could be mounted under the edge of the current work platform or on the mesh frame. The main purpose is trying to balance out the exposure on the underside of the mesh frame. Spare accelerometer cables for both uniaxial and triaxial accelerometers were purchased to avoid delays if they are damaged during testing. New accelerometers with lower ranges more suited to some of the tests were purchased. New mechanical filters were purchased. The new less expensive filters are made from polycarbonate and it was assessed they should function better as they do not separate like the metal cased ones seem to do. 2.4.4

Data Storage and Archiving

A centralised data storage was established for all dynamic testing, video recordings, data outputs, photos and analysis. This enables access by all relevant project staff to the files. This is especially important for accessing data, particularly large files, from outside Kalgoorlie via the Curtin University VPN.

2.5 2.5.1

THEORETICAL DEVELOPMENTS Force Transfer and Displacements

The selection of instruments and their locations are based directly on the force transfer and displacements in the various test configurations as presented and discussed in the following sections. In all cases, “freebody” diagrams were used. The equilibrium of each component in the test configuration forms the basis for the “engineering analysis” of a test and results in the reinforcement or surface support system performance being expressed in terms of a force-displacement response and energy absorption. Comprehensive free body diagrams have been developed to identify clearly the force interactions between all the components involved during a dynamic test of reinforcement systems, mesh and shotcrete panels and combinations of reinforcement and support panels 2.5.2

Reinforcement

The force transfer mechanisms in a reinforcement system test are shown in Figure 2.2. The equilibrium analysis was presented both by Thompson et al. (2004) and in the final report for MERIWA Project M349.

14


½PA

½T EA

½T EA

½PA

FRA

½mDBg

½mDBg ½T A

½T A

FAB

FAB

mPAg m Bg

m Bg

½FPJ

PB

½FPJ

PB

ANCHOR ZONE FRJ COLLAR ZONE ½FPJ

½FPJ

mPCg

½T C

½TC

½mLg

½mLg

FRC

½FSL

½FSL

½PC

½PC

½TEC

½TEC

Figure 2.2: Free-body diagram showing load transfer mechanisms within a reinforcement system.


15

2.5.3

Mesh

A free body diagram similar to that developed for a reinforcement system was developed for the mesh test and is shown in Figure 2.3 (ignoring the presence of the reinforcement). The frame mass and load transfer from the mesh to the beam are included in the analysis section of the software. 2.5.4

Shotcrete

The free body diagram for a shotcrete test are similar to those for a mesh test with the major difference being the self-weight of the shotcrete panel needing to be included in the analysis of loading and energy calculations. The free body diagram for a shotcrete test (ignoring the presence of the reinforcement) is shown in Figure 2.4. 2.5.5

Combined Systems

The free body diagrams for a reinforcement system combined with mesh and shotcrete panels are shown in Figure 2.3 and Figure 2.4, respectively.

16


PA

½PF

½PF

½PF

PA

½PF

½MDB

½MDB PA

½PF

FAB

½PF FAB

MPA MB

MB FRJ ½MFM

½MFM

PB

½ ML

½FM

½FSL

MPC

PB

½ ML

½FSL

FRC

½FM

½FPS

½FPS

½FEP

½FEP

FRC

Figure 2.3: Free body force diagram for dynamic testing of combined reinforcement and mesh panels.


17

½P PA

½P PA F RA

½P PA

½P PA

½M ABg

½M ABg M APg

½P AB

½PFB

½PFB ½P J

F RJ

½P AB

½P J

½M Bg

½M Bg

PB

PB ½M Fg

½M Fg ½M Cg

½M Cg M CPg

½P CS

½P SF

¼M SSg

¼ PE

¼ P EC

½P SF

½P CS

F RC

½M SCg

½M SCg

½P CP

¼ P EC

½P CP

¼M SSg

¼ PE

¼M Sg

¼ P SS

¼M Sg

½F RC

½F RC

½F RC

½F RC

¼ P SS

Figure 2.4: Free body force diagram for dynamic testing of combined reinforcement and rock substrate/shotcrete panels.

2.5.6

Summary

The free body force diagrams and associated component displacements are both used to refine the requirements for types of instrumentation and their locations on the various components. These diagrams are also key aspects of the design and development of the data analysis software.

18


2.6

DYNAMIC TEST DATA ANALYSIS SOFTWARE

A prime requirement for the development of the WASM Dynamic Test Facility was the development of associated filtering and processing of the data from the acceleration and displacement sensors to calculate the dynamic force-displacement responses for reinforcement and support systems. The WASM Data Analysis Software was developed in-house and reported in the final reports fo r MERIWA Project M349 and M349A. A User Manual for the software has been written and is updated as new options and enhancements are added. In particular, the software has been expanded to enable the analysis of the response of reinforcement combined with either mesh or shotcrete panels. As implied earlier, the new data acquisition software saved the test data in a format that differed slightly from the previous version of the software. Primarily, the data file saved by the software was in the form of raw signals rather than scaled according to the calibration coefficients associated with each instrument. Secondly, it also became apparent that with time, some instruments were damaged and needed to be replaced and the number of instruments also increased. Accordingly, it was decided to change from a set configuration of instruments and associated calibration factors to a system whereby the instrument configuration was associated with each particular test and each instrument was identified by its serial number. In order to implement this system, a new DynamicUtility program was developed and its functions are detailed in the following section. 2.6.1

Dynamic Utility

The user interface for the software utility shown in Figure 2.5 is used to perform a number of functions associated with creating files to be analysed using the main test data analysis software. These functions are: 

Calculate the impact velocity from the laser break times and the distances between them and the top of the buffers.



Create a test configuration file.



Create the video data files from the Excel tracking file output from the ProAnalyst software.


19

Figure 2.5: User interface of the new Dynamic Utility populated with configuration data for a

combined reinforcement and mesh test.

20


2.6.1.1

Creation of Calibration Coefficients

To facilitate conversion of the raw data to scaled data a unique file associated with each test is created. The data in this file are shown in Figure 2.6

Figure 2.6: Instrumentation configuration data. 2.6.1.2

Data Scaling

The Dynamic Utility takes the data from the Excel information file shown in Figure 2.6 and scales the raw data to then be used for subsequent filtering and data analysis. 2.6.1.3

Conversion of Tracking Data

The final function involves a number of automatic searches within Excel files to find starting and end times and the creation of the “.vid” files used in the main data analysis software. Previously these searches and associated data manipulation were done manually in several steps.


21

2.7

DATA ANALYSIS PROCEDURE

The same basic steps are taken in analysing data from a dynamic test, irrespective of the test configuration. These steps are: 1.

Data Visualisation

2.

Data Filtering

3.

Saving of Filtered Data

4.

Re-Filtering Data

5.

Time Synchronisation of Data

6.

Engineering Analysis.

All these functions are performed using the data analysis user interface shown in Figure 2.7.

Figure 2.7: User interface for analysis of dynamic data. A typical analysis for a combined reinforcement and mesh test is detailed in Section 6 of this report. 2.7.1

Data Visualisation

Data may be inspected as a single channel or in combinations of any number of channels. This step can be used to identify channels that may have defective data and do not have to be processed.

22


2.7.2

Data Filtering

Due to their sensitivity, accelerometers have signals with a combination of frequencies (e.g. Figure 2.8) and the data cannot be used without filtering. On the other hand, displacement transducers and load cells have signals that do not require much filtering.

Figure 2.8: Typical accelerometer signal without processing. A number of filters are provided within the software. The most commonly used are the Fast Fourier Transform (FFT) and the Butterworth filter. The FFT may be used for all data but is mainly used for accelerometers. The Butterworth filter is used mainly for displacement transducers. 2.7.3

Saving of Filtered Data

A typical accelerometer response after FFT filtering is shown in Figure 2.9. Each filtered channel is temporarily copied to a user interface form prior to saving to a file.


23

Figure 2.9: Accelerometer response after filtering. 2.7.4

Re-Filtering Data

Often, it is found that the filter settings for a particular instrument need to be modified or an additional instrument needs to be included in the subsequent analysis. Previously, either of these requirements necessitated a complete re-filtering of all the channels required. Enhancements were made to the software to improve the efficiency of processing by allowing for an already saved filtered data file to be modified by deleting data and adding a new channel of filtered data or saving a channel with several different filter settings. This enhancement has proved invaluable and saved many person hours of lost processing time 2.7.5

Time Synchronisation and Other Adjustments of Data

A well-known effect of filtering is a small time shift between the original “real” time and the filtered data time. Previously, these small time shifts were performed by laboriously using Excel to shift the data. Again, to improve this process, another enhancement was made to the software to enable all channels to be synchronised to the same test impact start time. The signals may also be re-scaled at this time or shifted in amplitude for cases where the signal was not processed correctly earlier in the analysis. This enhancement has proved very invaluable in saving processing time since the adjusted data is displayed in a chart. 2.7.6

Engineering Analysis

The engineering analysis uses as input the filtered waveforms from the accelerometers, potentiometers, load cells contained in the file created by the WASM software and the file saved from Excel for the video displacement track of the loading mass and head of the reinforcement system.

24


2.7.6.1

Assumptions for the analysis

The assumptions required to analyse the filtered data are: 

The drop beam and support testing frames behave stiffly; that is, the displacements can be considered to be small compared with the reinforcement and support displacements.



The beam displacement, velocity and deceleration after impact are considered to be equal to the corresponding parameters for the buffers. This means that parameters may be measured for either the beam or the buffer piston.



Vertical movements only are considered in the analysis so the vertical components from the accelerometers are used and the rotational and horizontal components of acceleration (and displacements) are ignored.



Filtering data does not influence the overall outcomes from the results or the relative performance of the classes of reinforcement system classifications; however, it will affect details of the graphs.



The zeroing of the filtered data to a common impact time that corresponds to a start time from the digital video does not significantly influence the overall result; however, it does change the early shape of the response graphs.



The number of buffers in a test does not significantly affect the results. This was validated by testing samples of the same reinforcement system impacting on to either two or four buffers and comparing the resultant dynamic force-displacement responses.

Other than already noted, the other assumptions have also been validated as part of the testing programs of reinforcement, mesh and shotcrete panels. 2.7.6.2

Input Data Files

The filtered data file is imported first and all the data are added to a text list box and into an array in computer memory. The video file is then imported. Because the frame rate for the video file is different, during the import process additional data for the missing time stamps is interpolated assuming a linear variation. Also, the video file often has a later start time than the filtered data. This is automatically taken into account and the data then added to the text list box and the array in computer memory. 2.7.6.3

Analysis of Data

The WASM software uses the processed waveforms with the synchronised start time. The channels for analysis are selected using the interface form shown in Figure 2.10. It is possible to “drag and drop” more than one channel in to a text box. The software automatically determines the number of different channels and then averages the data for that parameter.


25

Figure 2.10: Interface used to select channels for analysis for a reinforcement test. The analysis of data is performed over a specified time period. The start of data processing also initiates the saving of the data analysis settings. Once again this enhancement during M417 has proven invaluable in reprocessing of data. The displacement, velocity, acceleration momentum, energy and force variations with time for all components can be reviewed. The force-displacement responses for the ground support component and buffers are also calculated. These data are saved automatically as a csv file that can be imported into Excel for further analysis or to enable charts to be created for several different systems in order to facilitate comparisons.

26


2.8

TEST REPORTING

A test report is produced for each test. The test report comprises a pre-test laboratory recording of data and after analysis a report on performance based on the data analysis and associated observations. 2.8.1

Laboratory Recording Sheet

A very important aspect of each test is the completion of a standard pre-test document which records the test and instrument configurations. The data recorded is necessary in order to perform the data analysis. 2.8.2

System Performance

Following data analysis, various key performance indicator charts are created and added to the standard test report.

2.9

TRAINING

An important consideration for the future functionality of the WASM Dynamic Test Facility is training of staff to perform the various functions required for setting up and conducting tests, data analysis and reporting. During the project, the following training was completed: 

Two people have been trained for setting up and conducting tests using the facility.



A training session on the use of the new video camera and associated tracking was attended by John Player, Agampodi (Ushan) De Zoyza and Moises Cordova.

2.10 SUMMARY OF THE WASM TEST FACILITY 2.10.1 Features of the Facility The strengths of the WASM Test Facility are its ability to: 

Test full scale systems (both reinforcement and support and combinations).



Integrate simulated rock mass with the reinforcement system to be tested. Used in conjunction with thick wall steel pipe to simulate underground rock mass confinement.



Large input energy available to test reinforcement systems and demonstrated that failure can be achieved in a single impact.



Replicate dynamic loading caused by an ejected rock mass.



Provide data from extensive instrumentation within the facility and systems tested.



Use extensive analysis techniques to develop dynamic force-displacement response curves, velocity, deceleration and energy time graphs of the systems tested.



Use a data analysis software and methodology to understand the critical loading conditions.


27

2.10.2 Limitations of the Facility Some perceived limitations in the facility relate to the financial and time considerations: 

The facility would appear to be the most expensive mining dynamic test facility ever to be constructed.



It is likely to have the highest unit test cost as sample preparation can be slow and expensive.



Probably has the longest set up time.

In common with most other testing facilities, WASM static and dynamic tests are carried out under axial load conditions that are not necessarily representative of the loading that can occur underground. In particular, rock movements may cause shear loading of a reinforcement system. The performance will be significantly affected by the quantity of available dilation on the shearing structure, how intact the rock remains that is applying the shear loading, the rate of debonding / fracturing between the reinforcement element and encapsulation medium. An important influence for performance is whether the shear displacement is concentrated at one location on the bolt or at several locations along its length. 2.10.3 Concluding Remarks The WASM Dynamic Test Facility has been independently assessed in two ways. Firstly, Professor Ted Brown, an internationally recognised authority in rock mechanics stated in his 2004 keynote presentation at the International Ground Support Conference held in Perth that: ”The most advanced dynamic testing system known to the author is that developed recently at the Western Australian School of Mines (WASM), Kalgoorlie”. Secondly, the facility and research team received a Special Commendation for Research and Development at the 2005 Western Australian Engineering Excellence Awards. It is worth noting these attributions were made prior to the improvements and enhancements made during Phase II (MERIWA Project M349A) and Phase III (MRIWA Project M417). As a final comment, it should be noted that after more than 10 years of experimental and routine testing, it remains very difficult to guarantee that all tests will be successfully monitored and the data able to be processed. In the four year period of M417, 113 tests were performed; of these, 98 were processed to produce meaningful results. With this knowledge, in order to increase the success rate, a continual critical examination is made of quality assurance procedures at all stages of the process from sample preparation, set up and monitoring through to data processing and reporting.

28


3

TESTING OF REINFORCEMENT SYSTEMS

3.1

INTRODUCTION

An important component of an in situ reinforcement system is the rock surrounding the borehole. In particular, the interface between the internal fixture and the borehole wall influences the rate of load transfer. In laboratory tests with static loads it has been found that load transfer for reinforcement systems encapsulated with cement grout is controlled mainly by the interface between the grout and the element. For reinforcement systems such as those within the Continuous Friction Coupled category, the load transfer is directly between the element and the borehole wall. These systems have not been tested in the laboratory to the same extent as encapsulated systems. Therefore, it was necessary to develop a method of creating a material that would simulate rock.

3.2

SIMULATED BOREHOLES

In the WASM Dynamic Test Facility, there are two basic types of simulated borehole; namely: 

a standard borehole where the main function is to provide confinement to a cement encapsulated reinforcement element,



a rough borehole where the main function is to simulate the profile of a borehole drilled into rock.

The following sections detail issues related to the simulated boreholes and particularly, the creation of a rough borehole into which reinforcement elements are driven or rotated in the field by a drilling jumbo. 3.2.1

Pipe Radial Stiffness

It is well known that the performance of reinforcement systems is influenced by the confining effects provided by the rock surrounding a borehole (e.g. Hyett et al. 1992). The radial stiffness provided by steel pipes can be varied by changing the wall thickness to simulate different rock confining conditions and this has been quantified in the WASM Dynamic Test Facility. 3.2.2

Simulated Rock Material Selection

The development of a suitable material and methodology to create a simulated borehole with roughness and strength similar to a borehole in rock was an evolutionary process and resulted from three decisions: 1.

The simulated hole should be constructed as a single piece and not two half shells clamped together.

2.

The hole was to be drilled by an airleg machine, or jumbo, rather than poured about a polystyrene mould of the required dimensions that was later removed.

3: Testing of Reinforcement Systems

29

3.

The selection of a high strength non-shrinkage construction grout with addition of b a s a l t aggregate to produce a concrete core aided in the improvement of drill performance and increase of the Young's Modulus of the concrete compared to a standard grout.

3.2.3

Preparation of Simulated Boreholes

Many rough simulated boreholes in pipes were fabricated and used in a number of testing programs requested by sponsors BHP Billiton Nickel West, DSI and CODELCO and for the combined reinforcement and mesh testing. A number of improvements were made in regard to the centralizing of the simulated borehole. Also new grout mixes were trialled to achieve compressive strengths of over 50MPa after 2 days. Figure 3.1 shows details of sample preparation prior to and after cement grouting. Two centralizers were used to maximize load transfer. However, it was found that they interfered with the grout flow up the hole. An alternative method was then used in which the steel pipe was filled from the top with the cement grout prior to the insertion of the reinforcing elements.

Figure 3.1: Details of a) sample preparation and b) following cement grouting. As a consequence of incomplete encapsulation during sample preparation, a small proportion of bolts from the CODELCO program were not tested. Figure 3.2 shows a typical heavy pipe material used to simulate very stiff rock mass confinement.

30


Figure 3.2: Heavy pipes ready for cement grouting. 3.2.4

Reinforcement Systems

Figure 3.3 shows some of the DSI bolts available for installation at WASM. Three threaded bars and three Posimix elements having a 1 m de-bonding length were used in combination with Geobrugg mesh. All the rock bolts were encapsulated using cement grout. The Posimix bolts having 1.7 m de-bonded length were tested to characterise the thread-nut interaction at the collars. Finally, the Posimix bolts having 1.4 m debonding lengths were tested to determine the maximum energy absorbing capabilities of the bolt.

Figure 3.3: Details of DSI Posimix and Threaded rebar to be tested at WASM.


31

The Posimix bolt has proven that it can mix the resin successfully; therefore testing was undertaken in cement grout to facilitate the preparation of samples. The results showed that the Posimix bolt is the only bolt that can transfer load equally effective in cement and resin grouts. Figure 3.4 shows the rock bolts that were supplied by CODELCO. All bolts were encapsulated with cement grout as per the current practice at the El Teniente Mine.

Figure 3.4: Details of some of the CODELCO bolts tested at WASM.

3.3

TESTING PROGRAMS

The testing programs for sponsors involved both static and dynamic testing. 3.3.1

Newcrest Program

A total of 8 resin encapsulated rock bolts were tested. The program was commissioned by Newcrest and, consequentially, the details are confidential to them. Nevertheless, the dynamic performance is similar to the previously studied static testing at WASM (Villaescusa et al, 2007). In summary, if the resin is well mixed and the bolts are fully encapsulated, then the dynamic rupture of the bolt occurs at low energy levels (10 KJ or so) with minimum (300 93.4mm of maximum deformation and 83mm is the measured displacement 160mm of maximum deformation and 143mm is the measured displacement 367mm of deformation

33 (@100ms)

39 (@172ms)

>300 262mm of maximum deformation and 258mm is the 35 (@114ms) measured displacement Instrumentation Error 250mm 34 (@119ms) 127mm 25 (@75ms) 524mm 64 (@156ms) 196mm 30 (@100ms) >300 154mm yield Instrumentation Error 108mm 97mm

62mm 58


Results Rupture, failure occurred at the anchor end of the Roofex bolt Rupture

3000

Garford dynamic soli bar Garford dynamic soli bar

>300

Energy Dissipation (kJ)

154

213

64

Input Velocity Input Energy (m/s) (kJ)

Stable Stable, the plate severely deformed Rupture Rupture

Stable

Stable Stable Stable Stable Rupture Stable Stable Stable

Stable Stable

Figure 3.42: A comparison of energy dissipation for different reinforcement systems tested for CODELCO.


65

3.3.4

BHP Billiton Program

A total of 9 resin encapsulated D-Bolts (described previously) were tested in a program commissioned by BHP Billiton Perseverance Mine. The bolts were installed in previously prepared simulated boreholes. Figure 3.43 shows details of the mine site installation using a jumbo.

Figure 3.43: Mechanical installation of full scale rock bolts using resin encapsulation. A comparison of the dynamic load-displacement characteristics for all the tested D-bolts is shown in Figure 3.44. The results show that the majority of the bolts tested did not perform well due to problems (local enlargement of the diameter) with the simulated borehole diameter.

66


Dynamic Load (kN)

Very significant damage to surface support

Dynamic Deformation (mm) Figure 3.44: Dynamic Load-Displacement results for resin encapsulated D-Bolts.

Figure 3.45 shows some of the results for the same resin encapsulated reinforcement type. The performance was very inconsistent with both short and large displacements and, in one case, the reinforcement system developed sufficient load transfer to break the element. Figure 3.46 shows examples of poor and good resin mixing. Bolt labelled 183 showed poor resin mixing leading to large displacement during testing. Bolt labelled 178 mixed the resin significantly better – although some gloving by the resin cartridge can clearly be observed following axial splitting of the simulated holes. We believe that the cause of poor resin mixing was the enlargement of the simulated holes as shown in Figure 3.47. The enlargement was caused by problems with the borehole simulation and the results can be expected to simulate actual situations in which the hole integrity cannot be g u a r a n t e e d .


67

Figure 3.45: Different load transfer effectiveness for a similar rock bolt.

Glovin

Bolt

Bolt

Bolt 183 – example of poor resin mixing

Bolt

Glovin

Bolt

Bolt 178 – example of good resin mixing

Figure 3.46: Example of different resin mixing results for D-Bolts.

68


Bolt enlarged near the toe causing poor resin mixing

Figure 3.47: Example of poor resin mixing due to enlargement of simulated hole diameter.

3.3.5

DSI Posimix Bolts

The Posimix bolt is normally a reinforcement system fully encapsulated with resin and suitable for conditions of low energy dissipation (i.e. less than 50mm displacements). However, the bar can be decoupled as shown in Figure 3.48 to allow a specified amount of deformation according to the rock mass demand requirements of a particular mining situation. The bolt is installed as fully encapsulated; however, because of the decoupled region, the majority of the energy is dissipated by deformation of the steel bar within the decoupled length.

Figure 3.48: Cross sectional view of a fully encapsulated (decoupled) Posimix bolt.


69

3.3.5.1

Performance of Posimix Nuts

Posimix bolts having 1.7m debonded lengths were tested to characterise the thread-nut interaction at the exposed collars. For a typical 2.4m long bolt, this ensures an anchor length of 0.5m and a collar length of 200mm as the regions where load transfer can occur. This is the worst case scenario, as a minimum of 400mm collar length is recommended for load-transfer. In fact, 1.7m debonded lengths are not commercially available or recommended. Figure 3.49 shows the results from dynamic testing of such a configuration. Table 3.4 shows the energy dissipation, which is rated about 18 kJ – with limited testing. Dynamic Force‐Displacement of Debonded Posimix Rock Bolts_1700mm_NUT testing 300

Debonded Posimix Bolt_1700mm (205) Debonded Posimix Bolt_1700mm (206)

250

Debonded Posimix Bolt_1700mm (207)

Dynamic Force (kN)

200

150

100

50

0 0

20

40

60

80

100

120

140

Displacement (mm)

Figure 3.49: Dynamic testing of Posimix thread-nut geometry. Table 3.4: Energy dissipation from thread-nut interaction - debonded Posimix bolts.

DSI Debonded Posimix

Test Program

70

Bolt Sample Length No (mm)

Debonded Length (mm)

Impact Velocity (m/s)

Impact Energy (kJ)

Energy Deformation at Dissipation Discontinuity (kJ) (mm)

Result

205

2400

1700

6.16

36

29

98

Ruptured, Nut Stripped

206

2400

1700

5.18

26.4

18

74

Stable, threads started to shear half way through

207

2400

1700

5.56

30.4

N/A

93.9

Stable, poor result due to faulty grouting


3.3.5.2

Bolts Coupled at the Collar

For most practical applications, the Posimix debonded lengths should range from 1 to 1.4m. Figure 3.50 shows the results from dynamic testing of such configurations during this research period. Please note that bolt 173 is a fully bonded threadbar (failed at less than 40mm displacement) which is plotted for a comparison with the debonded bolts which dissipate a lot more energy. The energy dissipation is shown in Table 3.5. A significant increase of energy dissipation can be achieved by increasing the decoupled length from 1.0 to 1.4m. The results are very significant, given that the Posimix bolt installation can be mechanized to achieve immediate reinforcement action. In addition, bolt overcoring has shown the bolt to be fully encapsulated by the resin grout (Villaescusa et al., 2008).

Dynamic Force‐Displacement of Posimix Rock Bolts Debonded Posimix # 208 Decoupled Bolt_1400mm 1400 mm (208) # 209 Decoupled Debonded Posimix 1400 mm Bolt_1400mm (209) #210 Decoupled Debonded Posimix 1400 mm Bolt_1400mm (210) Debonded # 172 Decoupled Posimix Bolt_1000mm 1000 mm (T172) #176 Decoupled Debonded Posimix 1000 mm Bolt_1000mm (T176) Debonded Posimix #177 Decoupled Bolt_1000mm (T177) 1000 mm # 173 Fully coupled Posimix Bolt (173)

300

250

Dynamic Force (kN)

200

150

100

50

0 0

20

40

60

80

100

120

140

160

180

200

Displacement (mm)

Figure 3.50: Dynamic load-displacement response for a number of Posimix bolts.


71

Table 3.5: Energy dissipation – Posimix bolts.

Sample number

Bolt

Decoupled

Deformation at

Energy

length

length (mm)

discontinuity

dissipated

(mm)

(kJ)

(mm)

Test result

Demand category application

173

2400

0

35

7

Rupture

Low

172

2400

1000

115

26

Rupture

Medium

176

2400

1000

96

21

Stable

Medium

177

2400

1000

77

27

Rupture

Medium

208

2400

1400

171

42

Stable

High

209

2400

1400

113

29

Stable

High

210

2400

1400

128

33

Stable

High

3.4 REINFORCEMENT DATABASE Research to date has been focused to develop a performance criterion for comparison of a number of commercially available reinforcement systems. Comparisons based solely on energy absorbed are not sufficient, and the analysis must include, for example, dynamic force-displacement responses as well as practical considerations for total displacement allowed before rock mass unravelling occurs. Displacement is particularly important. For example, although a reinforcement system may have large displacement capacities (and hence energy absorbed due to the change in potential energy of the mass following impact) it may cause the rock mass to disintegrate to the point where the support system may not be able to hold the broken rock. Figure 3.51 shows a summary result of all testing undertaken to date at the WASM Dynamic Test Facility. An important consideration for any high energy absorbing strategy is to test the full reinforcement system including anchors, bolts and plate/hemispherical nut assemblies together. Systems that absorb large amounts of energy, but allow large deformations are not suitable for stability. The objective should be moderate, say 100-200 mm, reinforcement displacement which is compatible with stable surface support systems (mesh and shotcrete) at the boundaries of excavations.

72


Figure 3.51: WASM Reinforcement Capacity database (Player, 2012).


73

74


4

TESTING OF MESH SUPPORT SYSTEMS

4.1

INTRODUCTION

A number of new steel wire mesh products were tested on behalf of sponsors (Geobrugg and CODELCO) and a number of other new suppliers attempting to break into the market. The welded wire mesh testing and analysis for one new product being developed for the mining industry showed it did not appear to provide any advantages with regards to allowable deformation compared with conventional weld mesh.

4.2

WOVEN WIRE STEEL WIRE MESH TESTING

The main characteristics of the Geobrugg TECCO G80/4, DELTAX G80/3 and MINAX M85/2.7 mesh used in the testing program are listed in Table 4.1: Table 4.1: Main characteristics of TECCO G80/4, DELTAX G80/3 and MINAX M85/2.7 mesh. TECCO G80/4

DELTAX G80/3

MINAX M85/2.7

Mesh aperture

102 mm x 177 mm

102 mm x 177 mm

108 mm x 186 mm

Mesh aperture (inner circle)

80 mm

80 mm

85 mm

Wire diameter

4 mm

3 mm

2.7 mm

Wire strength

1,770 MPa

1,770 MPa

1,770 MPa

Breaking load of wire

22 kN

12.5 kN

10.1 kN

Tensile strength

190 kN / m’

110 kN / m’

90 kN / m’

Weight

2.6 kg / m2

1.45 kg / m2

1.5 kg / m2

Another series of tests under different boundary conditions on mesh reported by Windsor et al. (2004) show that the high-tensile diamond mesh does not unravel once a wire fails; this was observed with standard chain-link mesh by Ortlepp et al. (1999) and Vant Sint Jan et al. ( 2004). Due to the high-tensile steel, the weight of the mesh is very light in comparison to its strength and load capacity. It is adaptable to an irregular face and should be installed as tight to the face as possible in order to avoid inadmissible deflections.

4.3 4.3.1

Static Mesh Testing Introduction

In order to be able to quasi-statically test and compare the load-displacement capacity of surface support systems such as mesh (welded sheet mesh, diamond shaped high-tensile mesh, chain-link

mesh),

shotcrete panels and membranes, samples of each have to be tested under the exact same boundary conditions.

4: Testing of Mesh Support Systems

75

A first test program (reported by Morton, 2009) consisted of the static testing of mesh, shotcrete and membranes. During this test series the high- tensile mesh TECCO S95/4 was tested together with weld mesh panels. More details and analysis of those initial tests can be found in the work of Morton (2009) and Roth (2013). Further tests were conducted as part of the second stage of the program M349A and the third stage M417. Those additional test results are shown and discussed herein. 4.3.2

WASM Static Facility

The WASM static facility (Morton, 2009) consists of two steel frames, a lower frame used to support the sample and an upper frame used to provide a loading reaction (Figure 4.1). A mesh sample (1.3 m by 1.3 m) is restrained within a stiff frame that rests on the support frame. The boundary conditions attempt to simulate the continuation of the material beyond the limited sample boundary. The restraint system consists of high tensile bar, eye nuts and D shackles passing through a perimeter frame at allocated points to simulate a number of boundary conditions. A screw feed jack is mounted on the reaction frame. The screw feed jack is driven at a constant speed (4 mm per minute) and allows large displacements to be imposed on the mesh. Load is applied to the mesh through a spherical seat, to a 300 mm square, 35 mm thick hardened steel plate. The force is measured using a 50 tonne load cell mounted behind the loading point. Data acquisition is undertaken at two samples per second. Testing of a sample can take up to an hour to complete.

Figure 4.1: WASM Static Test Facility.

76


4.3.3

Description of the failure modes on the various mesh types

The failure mechanism of welded wire mesh is a measure of the mesh quality. Three different welded wire mesh failure modes have been identified during laboratory testing. These can be described as shear failure at the weld points, failure at the heat affected zone (HAZ) and tensile failure of the wire (Figure 4.2). Failure at the weld is an indication of the weld technology and quality control (dirty electrodes or dirty wire) during mesh manufacturing. Failure at the HAZ is caused by weakening of the wire during the welding process due to excessive weld head pressure and temperature, while tensile failure of the wire is controlled by the wire manufacturing process. For ground support, the preferred mode of failure is at the HAZ or through the wire. Consequently, the weld strength must be designed to have a strength at least equal to that of the line wire strength (Villaescusa, 1999).

Figure 4.2: Welded sheet mesh wire failure mechanism; left to right, tensile failure, weld failure, failure through heat affected zone. Only one failure mechanism was observed for the diamond shaped high-tensile mesh. The mesh failed on the edge of the loading plate either as a result of the plate cutting through the wire or the wires cutting each other at the “link”. This failure mechanism causes some variability in the test results. Generally only one or two wire strands broke and did not constitute a complete destruction of the mesh (no unravelling occurred on the high-tensile mesh). When the wires broke, the loading plate dropped through the opening (Figure 4.3).


77

Figure 4.3: Typical failure mode of the tests at the edge of the loading plate (hardened steel).

78


4.3.4

Static Test Results Summary

Table 4.2 shows the test result values for force and displacement at rupture. The detailed comparison includes the test results of different types of mesh. Figure 4.4 shows the force-displacement responses to static loading.

Table 4.2: Test results from the static tests. Test No.

Sample Description

Rupture Load (kN) 17.00 (no

Displacement Pre-test at Rupture Displacement (mm) (mm)

Energy at Rupture (kJ)

M094

Mild steel chain-link mesh (3.15mm, 95 x 95mm)

422.00

233.00

M095

Mild steel chain-link mesh (3.15mm, 95 x 95mm)

14.00

338.55

135.00

0,7

M087

DELTAX G80/2

28.70

205.00

71.00

1.37

M088

DELTAX G80/2

23.30

212.00

75.00

1.20

M089

DELTAX G80/2

23.64

211.00

77.00

1.20

T120

Heavy mild steel chain-link mesh (5mm, 100 x 100mm)

33.78

325.00

113.00

2.40

T121


54.03

345.90

102.00

3.86

T122


68.05

377.00

124.00

4.87

M017

Weld mesh (5.6mm, 100 x 100mm)

45.04

180.00

38.00

1.84

M025


46.38

181.00

45.00

1.76

M037


33.75

183.00

60.00

1.36

T146

MINAX M85/2.7

52.00

152.40

30.00

2.60

T147

MINAX M85/2.7

51.70

147.60

30.00

2.48

T146

MINAX M85/2.7

51.20

147.10

30.00

2.53

M099

DELTAX G80/3

50.90

182.00

1.00

3.24

M100

DELTAX G80/3

51.80

184.00

2.00

3.28

M101

DELTAX G80/3

49.90

181.00

2.00

3.11

M086

TECCO G65/3

no rupture

316.00

160.00

M090

TECCO G65/3

108.10

288.00

107.00

5.90

M091

TECCO G65/3

106.60

275.00

94.00

5.76

M096

TECCO G80/4

104.30

239.00

2.00

8.66

M097

TECCO G80/4

104.30

239.00

3.00

8.09

M098

TECCO G80/4

110.30

249.00

2.00

9.12

M085

TECCO G65/4

179.10

316.00

87.00

13.03

M092

TECCO G65/4

167.80

287.00

77.00

10.86

M093

TECCO G65/4

172.30

287.00

77.00

11.64


79

Figure 4.4: Force-Displacement chart from the static test results from Table 4.2. In the following graphs, the results from Table 4.2 are shown in a slightly different way. Figure 4.5 shows all the results for the force-displacement (at rupture) and Figure 4.6 shows the calculated energydisplacement.

80


Rupture Force (kN)

200 180

TECCO G65/4

160

TECCO G80/4

140 TECCO G65/3 120 100

DELTAX G80/3

80

MINAX M85/2.7

60 40

W eld mesh (5.6mm, 100 x 100mm)

20


0 0

100

200

300

400

DELTAX G80/2

Displacement (mm)

Figure 4.5: Force – displacement graph for all the static test results from Table 4.2.

14 TECCO G65/4 12 TECCO G80/4 Rupture Energy (kJ)

10 TECCO G65/3 8 DELTAX G80/3 6 MINAX M85/2.7 4


2


0 0

100

300 200 Displacement (mm)

400

DELTAX G80/2

Figure 4.6: Calculated energy – displacement graph for all the static test results from Table 4.2.


81

4.4 4.4.1

DYNAMIC TESTING Mesh Testing Configuration

Mass chocked in place

The mesh testing was performed using configurations similar to the one shown in Figure 4.7.

Loading mass Support frame boundary.

D-shackles.

Figure 4.7: Mesh sample and loading configuration immediately before dynamic testing. The mesh testing frame is bolted to a drop beam while the 1.3 m by 1.3 m mesh samples are held in place using threaded bar, shackles and eye bolts in the same configuration as the static test arrangement. A loading mass is placed into the centre of the restrained mesh. The loading mass consisted of a pyramidshaped bag filled with a known mass of steel balls (nominally 0.5 or 1 tonne). The loading area of the bag was 650 mm x 650 mm. A wooden prop was placed between the loading mass and the drop beam to prevent the mass “floating” during the initial free fall period.

82


4.4.2

Test Summary

The program of dynamic mesh testing is summarised in Table 4.3. Table 4.3: Summary of executed dynamic tests with various mesh types. Test No.

Sample description

T064 T065

Velocity [m/s]

Input energy Peak Load Rupture Load Displacement [kJ] [kN] [kN] [mm]

Energy absorbed by Comments mesh [kJ]

Loading mass [kg]

Loading area [mm]


515.00

d = 533

3.82

3.76

391.00

4.90

rupture


515.00

d = 533

3.91

3.93

94.20

410.30

5.44

no rupture

T066


515.00

d = 533

3.94

3.99

116.40

405.80

1.12

no rupture

T067


515.00

d = 533

4.89

6.15

119.50

414.80

1.32

no rupture

T068


515.00

d = 533

5.86

8.83

155.00

423.00

8.76

rupture

T069


990.00

d = 533

5.71

16.10

190.50

469.40

10.94

rupture

T053

Weld mesh (5.6mm, 100 x 100mm) (no rupture)

380.00

d = 533

3.83

2.78

182.10

1.10

no rupture

T054


380.00

d = 533

4.73

4.24

73.70

196.70

0.49

rupture

T055


380.00

d = 533

4.77

4.33

63.80

199.00

1.64

rupture

T083

MINAX M85/2.7 (rupture)

582.00

d = 533

1.96

3.74

86.60

86.60

203.00

2.12

Rupture of some wires

T084

MINAX M85/2.7 (no rupture)

582.00

d = 533

2.25

2.80

77.80

212.00

0.87

no rupture

T085

MINAX M85/2.7 (no rupture)

582.00

d = 533

1.94

3.28

73.60

233.00

0.98

no rupture

T080

DELTAX G80/3

582.00

d = 533

4.46

5.79

97.40

93.20

181.40

2.61

rupture

T081

DELTAX G80/3

582.00

d = 533

4.07

4.82

100.47

100.12

188.50

3.40

rupture

T082

DELTAX G80/3 (no rupture)

582.00

d = 533

3.79

4.18

89.40

188.05

2.62

no rupture

T056

TECCO G80/4

990.00

600 x 600

5.90

17.20

152.60

271.00

11.20

rupture

T057

TECCO G80/4

990.00

750 x 750

4.86

11.70

190.00

233.00

11.60

rupture

T058

TECCO G80/4 (no rupture)

990.00

750 x 750

4.36

9.40

159.00

208.00

9.30

no rupture

T059

TECCO G80/4

990.00

750 x 750

4.52

10.15

185.00

213.00

5.23

no rupture

78.20

71.39

Note: The input energy is not equal to the energy dissipated by the mesh. The test results are summarised as Force-Displacement and Energy-Displacement in Figure 4.8 and Figure 4.9, respectively.

200 180

TECCO G80/4

160

TECCO G80/4 (no rupture)

140 Force (kN)

DELTAX G80/3 120 DELTAX G80/3 (no rupture)

100 80 60


40

Heavy mild steel chain-link mesh (5mm, 100 x 100mm) No rupture

20


0 0

50

100 150 200 250 300 350 400 450 Displacement (mm)


Figure 4.8: WASM dynamic test results, Force-Displacement capacity.


83

14 TECCO G80/4 12 TECCO G80/4 (no rupture) 10 Energy (kJ)

DELTAX G80/3 8 DELTAX G80/3 (no rupture) 6 Heavy mild steel chain-link mesh (5mm, 100 x 100mm)

4

Heavy mild steel chain-link mesh (5mm, 100 x 100mm) No rupture

2


0 0

50

100

150 200 250 300 Displacement (mm)

350

400

450


Figure 4.9: WASM dynamic test results, Energy-Displacement capacity.

4.5 MESH DATABASES Figure 4.10 shows the WASM static database for galvanized weld mesh strength and deformability. The effect of wire diameter and failure mode can be clearly seen. The variability shown is due to the different dimensions and manufacturers of the products tested. Figure 4.11 shows detailed results for 5.6 mm diameter galvanized welded wire mesh where failure mode and corrosion effects are shown to significantly influence the results (Hassell et al. 2010). Static results for woven mesh are shown in Figure 4.12. The high overall capacity offers a potential for improvement compared with conventional weld mesh. Furthermore, woven mesh installation can be fully mechanized, thereby potentially increasing productivity and development rates.

84


60 Galvanized welded wire m esh

Static Rupture Force (kN)

All failure modes, ɸ = 5.6 mm Wire failure, ɸ = 5.0 mm Weld

40

failure, ɸ = 5.0 mm Wire failure, ɸ = 4.95 mm Wire failure, ɸ = 4.85 mm

30

Wire-weld failure, ɸ = 4.75 mm Wire-weld failure, ɸ = 4.65 mm

20

10

0 0

20

40

60

80

100

120

140

160

180

200

220

160

180

200

220

Static Displacement (mm) 2.0 Galvanized welded wire m esh

Static Rupture Energy (kJ)

1.8

All failure modes, ɸ = 5.6 mm Wire failure, ɸ = 5.0 mm Weld

1.6

failure, ɸ = 5.0 mm Wire

1.4

failure, ɸ = 4.95 mm Wire

1.2

Wire-weld failure, ɸ = 4.75 mm Wire-weld failure, ɸ = 4.65 mm

failure, ɸ = 4.85 mm

1.0 0.8 0.6 0.4 0.2 0 0

20

40

60

80

100

120

140

Static D i s p l a c e m e n t (mm)

Figure 4.10: Summary of static rupture force and energy-displacement for galvanised welded wire mesh with different wire diameters.


85

60

Static Rupture Force (kN)

Galvanized welded wire m esh Non corroded, wire failure, ɸ = 5.6 mm Non corroded, HAZ failure, ɸ = 5.6 mm Non corroded, weld failure, ɸ = 5.6 mm

50

Lightly corroded, wire failure, 5.0 mm

REPORT NO. 312 Dynamic Testing of Ground Support Systems

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