Keywords: Earth Retaining Structures, Cantilever Retaining Wall, Basement Wall, Stepped ..... Horizontal members spaced between vertical cantilevered posts. ... To increase the durability of this type of basement construction, steel rebar.
Automated Design of Earth Retaining Structures
By
Muhammad Hamad Junaid Ahmad
A final year project thesis presented to the University of Engineering and Technology Peshawar in partial fulfilment of the requirements of the degree of Bachelor of Science in Civil Engineering (Session 2013-17)
Peshawar, Khyber Pakhtunkhwa, Pakistan
i
July 2017
ii
Automated Design of Earth Retaining Structures Submitted by Junaid Ahmad Muhammad Hamad
Supervised by:
________________________ Prof. Dr. Bashir Alam (Chairman CED, UET Peshawar)
Approved by:
________________________ Prof. Dr. Bashir Alam (Chairman CED, UET Peshawar)
DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR, PAKISTAN iii
Table of Contents
Table of Contents ........................................................................................................................... iii Abstract ......................................................................................................................................... vii Acknowledgements ...................................................................................................................... viii List of Figures ................................................................................................................................ ix List of Tables ................................................................................................................................... x Introduction ............................................................................................................. 2 1.1
Motivations ...................................................................................................................... 2
1.2
Objectives ........................................................................................................................ 3
1.3
Scope ............................................................................................................................... 4 Literature Review .................................................................................................... 5
2.1
Retaining Wall ................................................................................................................. 5
2.2
Types of Retaining Walls ................................................................................................ 5
2.2.1
Masonry or Concrete Walls: .................................................................................... 5
2.2.2
Counterfort Retaining Walls .................................................................................... 5
2.2.3
Buttress Retaining Walls ......................................................................................... 6
2.2.4
Gravity Retaining Walls .......................................................................................... 6
2.2.5
Rubble Masonry Walls ............................................................................................ 6
2.2.6
Crib or Gabion Walls............................................................................................... 6
2.2.7
Wood Retaining Walls ............................................................................................ 6
2.2.8
Anchored (Tieback) Walls....................................................................................... 7
2.3
Basement Walls ............................................................................................................... 7
2.4
Types of Basement Walls ................................................................................................ 7 iv
2.4.1
Masonry Basement Wall: ........................................................................................ 7
2.4.2
Poured Concrete Basement Wall: ............................................................................ 7
2.4.3
Precast Panel Basement Wall: ................................................................................. 8
2.5
Sheeting and Shoring....................................................................................................... 8
2.6
Types of Sheeting and Shoring........................................................................................ 8
2.6.1
Raking Shores:......................................................................................................... 8
2.6.2
Flying Shores: .......................................................................................................... 8
2.6.3
Dead Shores: ............................................................................................................ 9
2.7
Building Codes for Retaining Structures ......................................................................... 9
2.8
Forces on Retaining Walls............................................................................................... 9
2.8.1
Lateral Earth Pressure............................................................................................ 10
2.8.2
Surcharge Loads .................................................................................................... 13
2.8.3
Adjacent Footing Loading ..................................................................................... 13
2.8.4
Wind Loads ........................................................................................................... 13
2.8.5
Impact Loads ......................................................................................................... 13 Methodology.......................................................................................................... 14
3.1
General Procedure: ........................................................................................................ 14
3.2
Requirements: ................................................................................................................ 15
3.2.1
Retaining Wall: ...................................................................................................... 15
3.2.2
Restrained Retaining Wall / Basement Wall: ........................................................ 15
3.2.3
Sheeting and Shoring:............................................................................................ 16
3.3
Implementation:............................................................................................................. 16
3.3.1
Data Collection: ..................................................................................................... 16
3.3.2
Analysis: ................................................................................................................ 18
3.3.3
Design:................................................................................................................... 22
3.4 3.4.1
Testing: .......................................................................................................................... 23 Hand Calculations: ................................................................................................ 23 v
3.4.2 3.5
Retaining Wall Design Application:...................................................................... 24 Results: .......................................................................................................................... 27
3.5.1
Overturning: .......................................................................................................... 27
3.5.2
Sliding ................................................................................................................... 28
3.5.3
Bearing Capacity: .................................................................................................. 29
3.5.4
Eccentricity ............................................................................................................ 30
3.6
Final Output:.................................................................................................................. 31 Conclusion ............................................................................................................. 32
4.1
Conclusions: .................................................................................................................. 32
4.2
Recommendation in Future Work ................................................................................. 32 References ............................................................................................................. 34
vi
Abstract Earth Retaining design is a multidisciplinary design process which involves the expertise of professionals from many disciplines of study including but not limited to structural, geotechnical, water resources and land planning. The project which this thesis describes is an attempt to automate the process of designing an earth retaining structure in accordance with the Codes mentioned in a later chapter.
Keywords: Earth Retaining Structures, Cantilever Retaining Wall, Basement Wall, Stepped Retaining wall
vii
Acknowledgements We are grateful to our Supervisor Prof. Dr. Bashir Alam, Chairman, Department of Civil Engineering, who is a consistent remainder of how hard work and dedication can lead a man to be highly respected and successful at the same time and whose persistent support and exceptional guidance has helped us accomplish a prestigious accomplishment in our lives.
We are also thankful to Engr. Waqar Ahmad for providing us resources and direction in the technical matter and for aiding us in the completion of the project.
viii
List of Figures Figure 1 Free Body Diagram of Lateral Forces ............................................................................. 10 Figure 2 Failure Wedge used for Coulomb Equation. ................................................................... 12 Figure 3 Methodology ................................................................................................................... 15 Figure 4 Wall Geometry, Retaining Wall...................................................................................... 16 Figure 5 Dimensions Illustrated .................................................................................................... 17 Figure 6 Material Properties, Retaining Wall ................................................................................ 17 Figure 7 Loading, Retaining Wall ................................................................................................. 17 Figure 8 Reinforcement, Retaining Wall....................................................................................... 18 Figure 9 Retaining Wall Forces ..................................................................................................... 18 Figure 10 Overturning Failure ....................................................................................................... 19 Figure 11 Sliding Failure ............................................................................................................... 20 Figure 12 Soil Uplift...................................................................................................................... 21 Figure 13 Design Steps.................................................................................................................. 23
ix
List of Tables Table 1 Overturning Analysis ---------------------------------------------------------------------------------- 27 Table 2 Graph Overturning ------------------------------------------------------------------------------------- 27 Table 3 Sliding Analysis ---------------------------------------------------------------------------------------- 28 Table 4 Graph Sliding ------------------------------------------------------------------------------------------- 28 Table 5 Bearing Capacity Analysis --------------------------------------------------------------------------- 29 Table 6 Graph Bearing Capacity------------------------------------------------------------------------------- 29 Table 7 Analysis Eccentricity ---------------------------------------------------------------------------------- 30 Table 8 Graph Eccentricity ------------------------------------------------------------------------------------- 30
x
1
Introduction 1.1 Motivations The underlying principle behind all structural design is the attempt to create safe and economical configuration of structure and its elements to sustain applied loads. This constitutes the practice of iteration to refine the design. Structural design follows a model of repetitive design and best pick selection. A model based on experience and knowledge of the forces is determined and analyzed, this model is either further refined or re-imagined to better aid in another attempt at solving the problem. This is a long and repetitive task which requires very precise calculations and must be performed by an experienced designer. This is an expensive and time-consuming task.
Design Changes are the second influential factors for time extension in construction projects in Pakistan. The first Being Law and Order Situation. [1]
As the law and order situation is unique to Pakistan and a few countries, Design Changes becomes the most prevalent Influential factor causing delays in construction projects.
“Change Order “was identified as the most common cause of delay identified by all the parties and about 70% of the projects experienced time overruns. [2]
The most important and highly ranked consultant related delay causes in construction industry of Pakistan are changes in drawings, inadequate consultant experience, preparation and approval of drawings, inaccurate site investigation, contract management, and slow response and inspection. [3]
2
There is an immense need of IT strategy plan which can improve the current practices in construction industry of Pakistan. [4]
In the modern world where computer technology has reached such a potential that the most daunting task which humans faced a few decades ago can be solved with the click of a button, the most amazing feats of science and engineering have been accomplished with the help of the amazing potential of computing in the modern age. The barrier to entry in this modern realm is the knowledge of programming and basic computer engineering.
The remaining problem is that embarking on a task to automate a manually solvable problem requires an initial investment of time and a professional with the knowledge of how to accomplish the task. There are two possible reasons why this process is not implemented already in Pakistan. One being the lack of knowledge about this process and the benefits of it. The second being the lack of willingness to let go of old processes and lack of confidence on the newer ones.
1.2 Objectives The analysis and design of Earth Retaining Structures is usually accomplished by following a set line of processes which can be automated, our task in this project is to attempt to provide a solution for this problem.
The objective of this thesis is to demonstrate a working model of various retaining wall analysis and design applications which may aid in the design of Earth Retaining structures which are more safe, economical and faster to design. This will lead to more time for engineers to work on more productive and imaginative tasks which may in turn take forward the collective engineering discipline.
3
1.3 Scope The scope of this project is the creation of programs for the analysis of a) Cantilever Retaining Wall b) Stepped Retaining Wall c) Concrete Basement Wall d) Sheeting and Shoring Structures
4
Literature Review 2.1 Retaining Wall A retaining wall is a built element which retains water, soil or other materials, when there is a sudden change in height [5], or it is a wall that provides support horizontally for nearly vertical or vertical slope of soil. [6]
2.2 Types of Retaining Walls Listed below are some common types of retaining walls. 2.2.1
Masonry or Concrete Walls:
Masonry stems are of thickness 200 to 300 mm made of concrete block masonry units which is partially or fully grouted and usually reinforcement bars are used in design section. Higher walls are made up to 300 mm thicker at the base which then tapered to 8 inches as reducing the retaining soil depth. Concrete walls are constructed as vertical exposed face with inner shape tapered for economy purpose. Hybrid walls can also be constructed, made of concrete and masonry, using molded concrete at the foundation where more strength is required then using masonry as higher up the wall.
2.2.2
Counterfort Retaining Walls
Counterfort wall consists of wing walls starting from the heel into the arm. The arm in between counterforts is Slender and spans laterally between counterfort walls. Counterforts exhibit as cantilevered member and these are Structurally effective because counterforts are increasing to the wide base when moments are greater.
5
2.2.3
Buttress Retaining Walls
Buttress Retaining Walls are alike to counterfort but wings start from the external face of the soil. These walls are utilized in such locations property line constraints on the interior face offer narrow space for the Heel of a customary cantilevered retaining wall.
2.2.4
Gravity Retaining Walls
This kind of wall will rely on self-weight of the for stability instead of tying stem like cantilevering from a foundation.
2.2.5
Rubble Masonry Walls
This type of wall is normally used for landscape features and retaining less than about 1200 mm high. Stability of these is generally verified for these walls and on rule-of-thumb basis size of the wall is made fixed- However higher height are needed evaluation for stability, overturning, sliding and it is also verified that minimal or no flexural tension do exist within the wall as these members are generally unreinforced.
2.2.6
Crib or Gabion Walls
It is a type of wall whereby wire fabric baskets are filled with stones or rubble. Crib walls are different from the gabion technique whereby baskets are filled with stone or rubble. Other difference is to heap a pile of timbers and fill the voids with soil or rubble. Precast concrete crib walls are also type of gabion walls.
2.2.7
Wood Retaining Walls
These walls are usually utilized for lower height retaining walls. Wood retaining walls are normally consist of horizontally spaced wooden planks which are implanted into the earth or fixed in concrete. Horizontal members spaced between vertical cantilevered posts. Pressure treated wooden posts are used, bet even with deterioration treated is not useful, and wooden walls are usually restricted to low walls due to height limitation by and strength of the planks. Railroad ties are also generally used for both vertical poles and cover.
6
2.2.8
Anchored (Tieback) Walls
This procedure is used for higher walls. Restraining the wall can be achieved by drilling anchors into the retained soil behind the wall outside the calculated failure plane in the retained soil. For higher walls, anchors can be provided in layers, these rods could be either post-tensioned or nontensioned and are connected to drill holes. Post-Tensioning technique is known as soil nailing. Other types of retaining walls include Tilt-up Concrete retaining walls, Segmental retaining walls(SRWs), Bridge Abutments, Sheet Pile and bulkhead walls etc.
2.3 Basement Walls A foundation wall which encloses a usable area under a building. [7]
2.4 Types of Basement Walls Listed below are some common types of basement walls.
2.4.1
Masonry Basement Wall:
A block or masonry wall is the least expensive for basement walls. This type of basement wall construction is made from cinder blocks. This method requires less time than other methods of basement construction. To increase the durability of this type of basement construction, steel rebar is sometimes used to reinforce the masonry wall. [10]
2.4.2
Poured Concrete Basement Wall:
Poured concrete basement are the most common and the choice that most people prefer. This type of basement construction starts by pouring footing for the basement foundation. After these are set, forms are used to hold the poured concrete wall in place as they dry. Poured concrete walls tend to be stronger than other types of basement walls. Solid concrete is better able to resist cave-ins caused by lateral pressures of water, earth, and wind. More fire resistance-because solid concrete is dense and is joint free. More resistant to waterconcrete has fewer and smaller voids than concrete block. [1]
7
2.4.3
Precast Panel Basement Wall:
Precast panel basement wall construction is the method where the walls are molded at another location. Then the walls are transported to the building and place on footers. This type of basement construction is quite strong but is not as commonly done as poured or block basements.
2.5 Sheeting and Shoring Shoring is the process of temporarily supporting a building, vessel, structure, or trench with shores (props) when in danger of collapse or during repairs or alterations. Shoring comes from shore a timber or metal prop. [12] Material, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing, sometimes over strapping to create a rain screen. [13]
2.6 Types of Sheeting and Shoring Listed below are some common types of sheeting and shoring. 2.6.1
Raking Shores:
Raking shores is a system of giving temporary support to an unsafe wall. The construction of raking shores, also known as inclined shore, varies with the conditions of site. A wall-plate is fixed against the unsafe wall with hooks. The wall-plate is further secured to the wall by means of needles. At their base, the rakers are supported by a sole piece bedded in an inclined position in the ground. 2.6.2
Flying Shores:
It is a system of providing temporary supports to the party walls of the two buildings where the intermediate building is to be pulled down and rebuilt. All types of arrangements of supporting the unsafe structure in which the shores do not reach the ground come under this category. They flying shore consists of wall plates, needles, cleats, horizontal struts (commonly known as horizontal shores) and inclined struts arranged in different forms which varies with the situation. In this system, also the wall plates are placed against the wall and secured to it. A horizontal strut is placed between the wall plates and is supported by a system of needle and cleats. The inclined struts are supported by the needle at their top and by straining pieces at their feet. The straining piece is also known as straining sill and is spiked to the horizontal shore. The width of straining piece is the same as that of the strut. 8
2.6.3
Dead Shores:
This is the system of shoring which is used to render vertical support to walls and roofs, floors, etc. when the lower part of a wall has been removed for the purpose of providing an opening in the wall or to rebuild a defective load bearing wall in a structure. The dead shore consists of an arrangement of beams and posts which are required to support the weight of the structure above and transfer same to the ground on firm foundation below.
2.7 Building Codes for Retaining Structures There are a number of building codes for designing retaining walls. A few of these codes are as follows: ●
American Concrete Institute (ACI 318).
●
International Building Code (IBC).
●
California Building Code (CBC 07).
●
Uniform Building code (UBC 97).
●
Indian Standards (IS).
●
AASHTO LRFD, Bridge Design Specifications 2007 (AASHTO LRFD BDS 2007).
●
National Fire Prevention Association, Building Construction and Safety Code (NFPA 5000)
●
USACE Design Manuals (USACE).
2.8 Forces on Retaining Walls Following loads are considered for retaining design: ●
Lateral Earth Pressure
●
Surcharge Loads
●
Axial Loads
●
Adjacent Footing Loads 9
●
Wind on Projecting Stem
●
Impact Forces
●
Seismic Earth Pressure
2.8.1
Lateral Earth Pressure
The primary design concern of retaining wall is to retain the earth pressure exerted by the backfill. Theories for pressure exerted by the lateral earth are presented on basis of sliding soil wedge theory. The wall will fail along the plane forming soil triangular wedge of soil along the rupture plane and wall must retain this wedge of soil. There are normally two basic procedures which are used to calculate lateral earth pressure i.e., Coulomb Method and Rankine Method
Figure 1 Free Body Diagram of Lateral Forces
2.8.1.1 Coulomb Earth Pressure Method C.A. Coulomb (ca. 1776) worked for the first time for designing retaining wall, he made following assumptions for design simplification purpose.
1. Soil is homogeneous and isotropic and having internal cohesion and friction. 10
2. The friction resistance factor is distributed linearly along the rupture plane and the soil to soil friction coefficient is f = tan Ø.
3. Rupture surface and backfill surface both are planar in nature i.e. it can be inclined but cannot be irregular surface.
4. The failure wedge body is a rigid structure which do not change the shape and this body as whole translates.
5. There is a frictional force developed due to translation on the surface between the wedge body and inner surface of the wall along which the failure wedge slides.
6. Failure of the structure is taken as plane strain problem. Formula for Ka coefficient of friction is provided by Coulomb as, 𝐾𝑎 =
sin2 (𝛼 + 𝛽) 1 2
sin(∅ + 𝛿) sin(∅ − 𝛽) 2 sin2 𝛼 sin(𝛼 + 𝛽) [1 + ( ) ] sin(𝛼 − 𝛿) sin(𝛼 + 𝛽)
Ka: Coefficient of active pressure : Angle of internal friction : Angle of backfill slope : Angle of friction between soil and wall : Slope angle of the wall which is measured from horizontal (equal to 90 degrees for vertical wall)
11
Figure 2 Failure Wedge used for Coulomb Equation.
2.8.1.2 Rankine Earth Pressure Method Rankine (ca. J 857) developed the Coulomb Equation and it is more simplified form of Coulomb Equation. He discarded the friction between soil and wall interface, as such it is conservative method for retaining wall design. Rankine formula for active earth pressure is given by:
12
𝐾𝑎 = cosβ
𝑐𝑜𝑠 ( 𝛽) − √(cos2 𝛽 − cos2 𝛼) 𝑐𝑜𝑠 ( 𝛽) + √(cos2 𝛽 − cos2 𝛼)
: Backfill slope angle : Internal friction angle of soil
2.8.2
Surcharge Loads
Surcharge load is an additional load applied vertically on top surface of the soil above the wall. These loads can be from highway, paving adjacent footing or parking.
2.8.3
Adjacent Footing Loading
If in case any adjacent footing overlays the soil wedge area, this surcharge load will exert an additional lateral pressure against the stability of the wall. Hence this kind of loading must be taken into account for stability calculations.
2.8.4
Wind Loads
When the wall is extended above the grade, wind pressure exerts additional stress which ultimately leads to additional overturning force.
2.8.5
Impact Loads
For car parking adjacent to retaining walls and wall projections are extended above the horizontal grade, walls must be designed for impact load exerted by colliding the car bumpers.
13
Methodology
3.1 General Procedure: All the project work was followed in this general approach. ●
Research into the Topic.
●
Design method analysis.
●
Reproduction of the design tasks in excel.
●
Verifying the Validity of the Design.
The first step of the process is to understand the need for the construction of these structures, we used a mix of resources including but not limited to books, video lectures and articles about the structures to better understand their need. The next logical step in this sequence is to understand the limit states and see how failure is possible in the structure, this gives a better idea about how to make a safe yet economical design. As the limit states for each structure vary, they are given in separate sheets in our output program. Following that mindset, they are also given separate mention in this document as well. After finding out the possible failure patterns of the structures the next step is to compute all the forces causing and resisting the specific type of failure. This is the analysis step. Now that the forces are identified the elements which cause change in these forces are tabulated and the effect of changing them is noted. Proportionality is determined.
Now going in reverse, the excel sheet is prepared by first specifying the elements which cause change in the forces, then the forces which may or may not cause failure. All the failure patterns are checked to see if any of the specified failure patterns occur, following this using code guidelines, the RC design of the structure is done.
14
Figure 3 Methodology
3.2 Requirements: 3.2.1
Retaining Wall:
For designing retaining wall following checks must be justified before design procedure: ●
Factor of safety against overturning of the retaining wall must be under the acceptable range i.e. greater than or equal to 1.5.
●
Allowable soil bearing pressure exerted by retaining wall must not be exceeding the foundation bearing capacity.
●
Factor of safety against sliding of retaining wall must be satisfied under the acceptable range (i.e. greater than or equal to 1.5).
●
There must be no tension in the soil. The Minimum Soil Pressure must be a positive number.
●
Stresses developed, by the loads imposed by retained soil, within the wall components are under the acceptable limits provided by code.
3.2.2
Restrained Retaining Wall / Basement Wall:
For designing restrained retaining wall following checks must be justified before design procedure: ●
Factor of safety against overturning of the retaining wall must be under the acceptable range i.e. greater than or equal to 1.5.
15
●
Allowable soil bearing pressure exerted by retaining wall must not be exceeding the foundation bearing capacity.
●
Stresses developed, by the loads imposed by retained soil, within the wall components are under the acceptable limits provided by code.
3.2.3
Sheeting and Shoring:
For designing retaining wall following checks must be justified before design procedure: ●
Flexure and Axial Capacity of the Pile members must be exceeding the demand
●
Shear Capacity must not exceed the demand.
●
Embedment depth of the pile must be determined
3.3 Implementation: 3.3.1
Data Collection:
The following properties are necessary for any design practice. ●
Geometry
Figure 4 Wall Geometry, Retaining Wall
16
Figure 5 Dimensions Illustrated
●
Materials
Figure 6 Material Properties, Retaining Wall
●
Loading
Figure 7 Loading, Retaining Wall
●
Reinforcement
17
Figure 8 Reinforcement, Retaining Wall
As the above properties can be widely varied and through them a proper design is possible, it has been left to the user to change. The application is not programmed to change these values.
3.3.2
Analysis:
Analysis steps vary for each type of structure, but they generally follow a similar pattern. 1. Innumerate all the forces of interest. 2. Resolve them into simple Components. 3. Calculate their resultants. 4. Find the moments required. 5. Compare them to satisfy the results. 3.3.2.1 Retaining Wall:
Figure 9 Retaining Wall Forces
18
3.3.2.1.1 Overturning: “Factor of safety against overturning of the retaining wall must be under the acceptable range i.e. greater than or equal to 1.5.” Keeping this principle in mind the Overturning Moment and Resisting Moment are calculated.
Figure 10 Overturning Failure
Factor of Safety = Resisting Moment / Overturning Moment 𝐹𝑂𝑆 = ∑𝑀𝑅/ ∑𝑀𝑜 ∑𝑀𝑅 𝑖𝑠 𝑡ℎ𝑒 𝑆𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑛𝑔 𝑀𝑜𝑚𝑒𝑛𝑡𝑠 ∑𝑀𝑜 𝑖𝑠 𝑡ℎ𝑒 𝑆𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝑂𝑣𝑒𝑟𝑡𝑢𝑟𝑛𝑖𝑛𝑔 𝑀𝑜𝑚𝑒𝑛𝑡𝑠
3.3.2.1.2 Sliding:
“Factor of safety against sliding of retaining wall must be satisfied under the acceptable range (i.e. greater than or equal to 1.5).”
19
Figure 11 Sliding Failure
𝐹𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑆𝑎𝑓𝑒𝑡𝑦 = 𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝐹𝑜𝑟𝑐𝑒 / 𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝐹𝑜𝑟𝑐𝑒 𝐹𝑂𝑆 = ∑𝑉𝑡𝑎𝑛𝛿 + 𝑃𝑝 / ∑𝐻
∑𝑉 𝑖𝑠 𝑡ℎ𝑒 𝑆𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝐹𝑜𝑟𝑐𝑒𝑠 𝛿 𝑖𝑠 𝑡ℎ𝑒 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝐹𝑟𝑖𝑐𝑡𝑖𝑜𝑛 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑜𝑖𝑙 𝑎𝑛𝑑 𝑏𝑎𝑠𝑒 𝑃𝑝 𝑖𝑠 𝑡ℎ𝑒 𝑃𝑎𝑠𝑠𝑖𝑣𝑒 𝑠𝑜𝑖𝑙 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ∑𝐻 𝑖𝑠 𝑡ℎ𝑒 𝑆𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝐹𝑜𝑟𝑐𝑒𝑠
3.3.2.1.3 Soil Uplift: “There must be no tension in the soil. The Minimum Soil Pressure must be a positive number.”
20
Figure 12 Soil Uplift
The ratio of eccentricity and sixth of Base width must be less than one.
𝐸𝑐𝑐𝑒𝑛𝑡𝑟𝑖𝑐𝑖𝑡𝑦 / (𝐵𝑎𝑠𝑒 𝑊𝑖𝑑𝑡ℎ / 6) ≤ 1 𝑒/(𝐵𝑤/6) ≤ 1
𝑒 𝑖𝑠 𝑡ℎ𝑒 𝐸𝑐𝑐𝑒𝑛𝑡𝑟𝑖𝑐𝑖𝑡𝑦 𝐵𝑤 𝑖𝑠 𝑡ℎ𝑒 𝐵𝑎𝑠𝑒 𝑊𝑖𝑑𝑡ℎ
3.3.2.1.4 Bearing Capacity: “Allowable soil bearing pressure exerted by retaining wall must not be exceeding the foundation bearing capacity. (i.e. greater than or equal to 3)”
𝐹𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑆𝑎𝑓𝑒𝑡𝑦 = 𝐹𝑜𝑢𝑛𝑑𝑎𝑡𝑖𝑜𝑛 𝐵𝑒𝑎𝑟𝑖𝑛𝑔 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 / 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑒𝑥𝑒𝑟𝑡𝑒𝑑 𝑏𝑦 𝑊𝑎𝑙𝑙 𝐹𝑂𝑆 = 𝑄𝑎/𝑃(𝑚𝑎𝑥) 21
𝑄𝑎 𝑖𝑠 𝑡ℎ𝑒 𝐹𝑜𝑢𝑛𝑑𝑎𝑡𝑖𝑜𝑛 𝐵𝑒𝑎𝑟𝑖𝑛𝑔 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑃(𝑚𝑎𝑥) 𝑖𝑠 𝑡ℎ𝑒 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑒𝑥𝑒𝑟𝑡𝑒𝑑 𝑏𝑦 𝑊𝑎𝑙𝑙
3.3.2.1.5 Structural Integrity: The Structure must withstand the pressure applied on it. In this regard, the two most important considerations are Flexural Capacity and Shear Capacity. The checks must be satisfied for the following segments. ●
Stem
●
Heel
●
Toe
3.3.2.2 Restrained Retaining Wall: The analysis steps for the restrained retaining wall are similar to the steps in simple retaining wall, except there are only three checks rather than five.
They are ●
Overturning
●
Bearing Capacity
●
Structural Integrity
3.3.3
Design:
After the safety of the structure is determined the next step in the process was to compute the RC design of the structures.
This process followed the following steps
22
Figure 13 Design Steps
3.4 Testing: Testing the program was done in a simple matter, A problem with solved solution was taken. This was first tested by hand calculations. The answer was then tested by the program. This made sure the program was working as planned. The testing was carried out in two steps.
Hand Calculations
Retaining Wall design Application
3.4.1
Hand Calculations:
The hand calculations were conducted in a systematic manner, in the following sequence 23
1. All Input Data about a specific Structure was noted. Including the geometry, Material Properties, Loading and Reinforcement. 2. Next the Forces were computed, this was done in a two-step manner. a. The force was calculated from the data using set formulae given from stated references and code guidelines. b. This force was then compared with the Sheet answers to verify it. 3. From this the Factors of Safety were computed on paper. 4. These were then compared to the Sheet answers for verification. 5. The RC design is done in a similar pattern.
3.4.2
Retaining Wall Design Application:
The next step in verification of the answers was to compare them with answers from a Third-Party Software Manufacturer. In this case the “ASDIP Retain” software was chosen. According to their Website, “For more than 25 years, ASDIP structural engineering software has been developed for practicing structural engineers to work cost-effectively, to complete common design tasks in less time.”
24
Figure 14 ASDIP Retain
25
Figure 15 ASDIP Retain
26
3.5 Results: Overturning: Table 1 Overturning Analysis
OVERTURNING TRIAL NO.
Custom
ASDIP
1
2.35
2.23
2
1.15
1.12
3
2.94
3.01
4
3.67
3.68
5
3.63
3.55
Table 2 Graph Overturning
OVERTURNING 3.55
3.63
3.01
2.94
1 2.35 2.23
1.12
1.15
2.23
2.35
Custom ASDIP
3.68
ASDIP 3.67
Custom
FACTOR OF SAFETY
3.5.1
2 1.15 1.12
3 2.94 3.01
27
4 3.67 3.68
5 3.63 3.55
3.5.2
Sliding Table 3 Sliding Analysis
SLIDING
TRIAL NO.
Custom
ASDIP
1
1.92
2
2
1.21
1.28
3
1.79
1.87
4
2.07
2.15
5
2.19
2.26
Table 4 Graph Sliding
SLIDING
1.79
2.26
2.19
2.15
1.87
2.07
1 1.92 2
1.28
1.21
Custom ASDIP
ASDIP
2
FACTOR OF SAFETY
1.92
Custom
2 1.21 1.28
3 1.79 1.87
28
4 2.07 2.15
5 2.19 2.26
3.5.3
Bearing Capacity: Table 5 Bearing Capacity Analysis
BEARING CAPACITY
TRIAL NO.
Custom
ASDIP
1
0.95
0.8
2
1.32
1.9
3
3.78
3.6
4
5.04
4.7
5
4.77
4.2
Table 6 Graph Bearing Capacity
BEARING CAPACITY
Custom ASDIP
4.2
4.77
3.6
1.32 0.8
0.95
1.9
3.78
FACTOR OF SAFETY
4.7
ASDIP 5.04
Custom
1 0.95 0.8
2 1.32 1.9
3 3.78 3.6
29
4 5.04 4.7
5 4.77 4.2
Eccentricity Table 7 Analysis Eccentricity
ECCENTRICITY
S.NO
Custom
ASDIP
1
1.28
1.31
2
3.3
2.98
3
0.74
0.6
4
0.25
0.23
5
0.34
0.39
Table 8 Graph Eccentricity
ECCENTRICITY ASDIP
Custom ASDIP
1 1.28 1.31
2 3.3 2.98
3 0.74 0.6
30
4 0.25 0.23
0.39
0.34
0.23
0.25
0.6
0.74
1.31
2.98
3.3
Custom
1.28
3.5.4
5 0.34 0.39
3.6 Final Output:
This portion of the document has been separately uploaded in ‘pdf’ format (3 files). Kindly, refer to that.
31
Conclusion 4.1 Conclusions: The Aim of the Project was:
To create an accurate and detailed solution to solving Earth Retaining Structure problems
To create a methodology for creating automated solutions to problems that can be used in the future to solve and automate solutions to Structural Design Problems.
Some Features of the Project are
The Product has reasonable results when compared with industry standard and expensive applications.
Most common Retaining Structures can be analyses and designed using the Software.
Though rigorous testing the failure pattern and the analysis of all the forces is accurate with only slight deviations from other Applications.
This procedure provides the designer a quick way to glance over third party designs which can help to make sure the resultant structure is stable and economical.
Quick changes to the design is now more accessible, this may reduce the load design changes brings upon a construction project as it can help reduce the expensive and timeconsuming workload of precise and tiresome calculations required to analysis and design an earth retaining structure.
4.2 Recommendation in Future Work This Project was planned in a modular format, it was engineered to be a stepping stone towards solving more complex problems in the future. 32
The project can easily be used to create a similar body of work for the analysis of Water Retaining Structure. It can be used with slight modifications to create solutions to problems related to Dams, Reservoirs, Barrages etc. It can also be used for further work in Earth Retaining Structures study like Abutments and sheet pile walls.
More work is still possible in the Retaining Structure as a costing mechanism and more streamlined design and analysis which recommends the dimensions of the wall can be added. This may take more time but it is a worthy project to invest time in.
33
References
[1] I. A. M. J. S. G. S. Shujaa Safdar Gardezia, "Time Extension Factors in Construction Industry of Pakistan," Fourth International Symposium on Infrastructure Engineering in Developing Countries, IEDC, 2014. [2] a. A.-H. Sadi A. Assaf, "Causes of delay in large construction projects," International Journal of Project Management 24, 2006. [3] X.-L. A. B. M.-u.-D. W. R. M. Haseeb, "Causes and Effects of Delays in Large Construction Projects of," Kuwait Chapter of Arabian Journal of Business and Management Review , 2011. [4] N. M. A. C. Z.A. Memon, "The Use of Information Technology Techniques in the Construction Industry of Pakistan," The Mehran University Research Journal of Engineering & Technology, 2012. [5] R. Hughes, Basics of Retaining Wall design. [6] B. . Das, Principles of Geotechnical Engineering, ed., vol. , , : Thomson Learning, 2006, p. . [7] McGraw-Hill Dictionary of Scientific & Technical Terms, The McGraw-Hill Companies, Inc., 2003. [8] K. . Terzaghi, Theoretical Soil Mechanics, ed., vol. , , : John Wiley and Sons, 1943, p. . [9] M. . Budhu, Soil Mechanics and Foundations, ed., vol. , , : John Wiley & Sons, Inc, 2007, p. . [10] EPP
Concrete,
"Types
of
basement
construction,"
[Online].
Available:
https://eppconcrete.com/types-of-basement-construction/. [11] Concrete
Network,
[Online].
Available:
https://www.concretenetwork.com/concrete/basements/types.htm. [12] "The
Oxford
English
Dictionary,"
,
.
[Online].
Available:
http://www.oxforddictionaries.com/words/the-oxford-english-dictionary. [Accessed 10 7 2017].
34
[13] Illustrated Dictionary of Architecture, 2007: The McGraw-Hill Companies, Inc..
35
