3D-Construction Applications III - Semantic Scholar

1st International Conference on Machine Control & Guidance 2008

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3D-Construction Applications III GPS-based Compaction Technology Kuno KAUFMANN*, Roland ANDEREGG** Ammann Switzerland Ltd.

Abstract GPS based compaction with vibratory rollers is finding its way onto building sites all over the world. Thanks to its ability to visualise the compaction process, what started out as an idea for providing users with an improved means of area-wide dynamic compaction monitoring has rapidly developed into a straightforward and effective method of process control. GPS based compaction links machine kinematics with job-integrated process measurement and control technology in the vibratory roller, thus establishing overall process control and monitoring.

Keywords GPS based Compaction Control, Quality Assurance/Quality Control in Road Building, GPS based Compaction Guidance, Visualization of Compaction Process

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INTRODUCTION

In road building, compaction machinery like vibratory rollers and single drum rollers aggregate the unbound (soil) and bound (asphalt) mixture. Mechanical compaction has the following objectives: • Achievement of minimum air voids for a given granulometry, so as to arrive at maximum density without damage to particles • Through so doing, achieves a road with uniformly high rigidity • Produce a structure that remains stable under subsequent traffic load Vibratory rollers are the means of compaction currently in use worldwide. They are subject to countryspecific requirements regarding the quality of compaction to be attained.

1.1 Compaction Process and Machine Technology

Figure 1: road building process, soil and asphalt compaction machines and field compaction test

Vibratory compaction machinery, single drum and tandem rollers are used to achieve the objectives mentioned above. They achieve the necessary degree of compaction, or rigidity, by making a number of passes over a given spot. This entails following a rolling pattern that depends on material emplacement conditions and machine parameters. Figure 1 provides an overview of the machinery most frequently used, a fully production program of compaction equipment is manufactured by the Ammann-Group, Switzerland, see www.ammann-group.ch.

3D-Construction Applications III

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1.2 GPS-Technology on the Job Site In addition to the automatic control of the compaction process by changing amplitude and frequency continuously and displaying the operator the optimum speed, the measurement of the soil stiffness kB and, additionally for asphalt layers, the measurement of the surface temperature T complete the “Intelligent Compaction“. These measurement values are calculated for at least each 360° revolution of the mechanical exciter, e. g. 25-50 times per second depending on type of roller. The automatic control of the roller parameters guarantees the optimal compaction result. The stiffness/rigidity measurement technology was developed during the last decade, see (ANDEREGG, R., 1998), (MOONEY, M. et al., 2007). Similarly important for the achievement of the optimum compaction result in practice are the following tasks: • Information about the achieved compaction value kB including the location coordinates (xi, yi, zi) • Information about the number of passes and the homogeneity of the achieved stiffness kB • Asphalt compaction data: asphalt temperature cooling rate, e. g. ΔT(xi,yi,tn)=T(xi,yi,tn)-T(xi,yi,tn-1) This information is available if the measurement data of the roller kB, T, etc. are combined with GPSdata xi, yi, (zi), Time t. (zi) is the vertical (out of plane) data with a lower accuracy compared to the inplane data xi, yi (HOFMANN-WELLENHOFF, B, et. al., 1997). The process could be displayed to the roller operator in real time, the visualisation of the process allows him optimal application of the compaction equipment.

Figure 2: Differential Global Positioning System (DGPS) in application on single drum roller for soil compaction

The compaction process guidance system ACEplus enables the roller driver to gain an in-situ-overview of the job site. The operator maximises his productivity while adapting the machine-use to the displayed compaction data. The accuracy of the ACEplus-data is dependent on the type of GPSreceiver. On job sites, contractors very often use RTK-GPS-systems (RTK: Real Time Kinematics) consisting of a GPS-receiver on the roller, a GPS base station and a reference signal between base and roller receiver (KAUFMANN, K. et al., 2002). This technology leads to an accuracy of the roller position of about ±5 cm, see figure 2 for technical description. Comparing the roller passes (xi, yi, tn), the ACEplus-system shows the operator the overlap of the different roller passes. The overlap is displayed through markers (MANSFELD, W., 1998).


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GPS-BASED COMPACTION CONTROL AND GUIDANCE

The basic idea of having a Continuous Compaction Control (CCC) on the job site is quite an old one. The application of controlled rollers ACE in combination with GPS-equipped visualisation ACEplus is the key to achieving this goal. The GPS-based compaction control and guidance is today’s answer towards fulfilling the increasing requirements of road construction,. The data acquisition and visualisation processing system ACEplus enables the user to maximise compaction equipment performance. The real-time visualisation of the compaction data on a PC screen maximises compaction process control and the benefit of using an automatic controlled roller. The Continuous Compaction Control enables the operator to recognise non-compactable material or still compacted areas on a job site immediately. Reasons why compaction machinery and GPS technology combined represent a system technology, see also (KAUFMANN, K. et al., 2002): • Surface compaction: machinery is mobile and requires several roller passes to complete the compaction process • 2-D movement: hitting the same spot twice means getting a second pass at the same location • Based on location and time, combined with compaction parameters such as material characteristics, surface temperatures, material rigidity, etc. • The degree of compaction attained is crucial to the overall success of construction • Compaction machinery as sensors: surface temperature, moisture measurement, determination of the degree of compaction • Compaction machinery in general vibrates • Vibration opens the possibility of job-integrated compaction measurement • Machines can regulate their compaction power Main conclusion GPS-based compaction control and guidance support the roller operator in achieving the optimal compaction result in a simple and efficient way. The supervisor on the job site is able to maximise the productivity of all the compaction machines on a certain job site. Last but not least, the contractor maximises the output of his resources.

2.1 Compaction Measurement and Control Technology Job-integrated measurement and control technology in vibratory rollers is based on analysis of the non-linear dynamics of the soil-machine system. Increasing compaction of the subgrade steadily alters the overall dynamics of the system considered in figure 3. At every stage of the operation, there is a differing optimum for the variable parameters of amplitude, frequency and roller speed in the machine and its vibration-inducing mechanism (ANDEREGG, R., 1998), (BRANDL, H., et al., 2000). Next to automatic parameter regulation, the roller also supplies a value for soil stiffness kB, which correlates directly with the degree of soil compaction. With homogenous soil, this correlation is independent of variable machine parameters; machine calibration is simple to perform without requiring specific adjustments to machine parameters. The calibration of the roller with standard compaction test devices is described in specifications, see (ADAM, D. et al., 2005).

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Figure 3: vibratory single drum roller; multibody nonlinear dynamics

In analytical terms, the steady-state dynamic behaviour of the soil-machine system is described with the help of the equation of motion according to: FB = − m d &x&d + me re Ω 2 cos(Ω ⋅ t ) + k G x d − x f + c G x& d − x& f + m d ⋅ g 0 = − m f &x& f + k G x f − x d + c G x& f − x& d + m f ⋅ g

(

)

(

where FB: soil-drum-interaction force

(

)

)

(

FB = k B xd + cB x&d

)

if F ≥ 0 B

FB ≡ 0 else

according to Figure 3. The dot notation signifies the differentiation with respect to time. md: drum mass [kg]; f: frequency of the excitation [Hz]; mf: frame mass [kg]; Ω: circular vibration frequency [Hz]; mere: eccentric moment of unbalanced mass [kgm]; xd: displacement of the drum; kB: soil stiffness [MN/m]; xf: displacement of the frame: cB: soil damping [MNs/m]; kG: suspension stiffness [MN/m]; cG : suspension damping [MNs/m] The nonlinearity is primarily caused by the one-side constraint between the drum and the soil: only pressure forces can be transmitted. Depending on the condition of the soil and the size of the soil reaction force, the machine lifts off from the subgrade at periodic intervals. The discontinuity caused in this way leads to nonlinearity, and it can be recognized by the occurrence of additional overtones corresponding to integral multiples of the excitation frequency. In addition, subharmonic vibrations may occur with a half, a quarter or an eighth (etc.) of the excitation frequency and its harmonics (THOMPSON, J. M. T. et al., 2002). Accordingly, the motion behavior of a dynamic compactor can basically be divided into linear behavior while the drum remains in contact with the ground, periodic nonlinear loss of contact, and finally bouncing/rocking as a chaotic dynamic state (ANDEREGG, R. et al., 2005). As shown in figure 3, the characterisation makes use of the time progression for the soil reaction force FB or the frequency analysis of the drum motion xd. The analytical description may take the form of a cosine series. The nonlinearity created by the periodic loss of contact between the drum and the soil can be represented as a function of the soil reaction forces. If the nonlinearity is increasing, the degree of freedom of drum and frame starts to interact and additional near-periodic vibrations with frequencies around 1/3f and 2/3f (f: excitation frequency) may occur, see figure 4


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(ANDEREGG et al., 2006), simulation program is according to (KAUFMANN, 2006). A general overview of such type of interaction is described in (SCHMIDT, G. et al., 1986), Chapter 6.

Figure 4: amplitude spectra for different static moment mere of a single drum roller

2.2 GPS-based compaction control & guidance technology The measured stiffness kB represents the mechanical parameters of the subgrade, from which the compaction can be read off. Meanwhile, the machine parameters optimally adjust themselves to specifically conditions. By linking these functions with location and time – the principal GPS parameters – it is possible to depict the overall compaction process, monitor it and visualise it to the machine driver. Visualisation is the silver bullet for process optimisation.

Figure 5: single drum roller with basic geometrical GPS job site data, display of stiffness kB and counting of the number of passes

Figure 5 shows parameters for GPS based logging of machine measurement parameters. Data for each layer and roller pass is stored in a digital coordinate grid, from where it may be visualised. When a section of the grid is rolled on a second or subsequent pass, the time and measured stiffness are logged and stored in the general form (xi, yi, (zi), time t, kBi value). Data management, processing and a realtime display that the driver can readily interpret form the key to GPS based compaction.

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TECHNOLOGY IN PRACTICE: APPLICATION KNOW-HOW

3.1 Data acquisition and management Recorded data is logged in a database in the general form {location (xi, yi, (zi)), time tn, roller pass n, stiffness kB, other parameters}. Calculating the number of roller passes is an initial analysis based on the search criterion (number n of points in time t1, t2,…, tn at a given location (xi, yi, (zi)) that has been previously logged. This information results in the following process information: • Number of roller passes, i.e. the number of times grid element (xi, yi, (zi)) has been logged • Degree of compaction achieved, i.e. kB at location (xi, yi, (zi)), at the time tn of the most recent, nth roller pass • Compaction increase at location (xi, yi, (zi)), i.e. kB(tn)-kB(tn-1):=ΔkB(tn). Figure 6 represents the compaction graphically. Optimal compaction is achieved when the kB value at location (xi, yi, (zi)) attains the desired value kB|Target within as few roller passes as possible, and no further increase in compaction is possible, i.e. ΔkB(tn)=0. An area is optimally compacted when this condition has been achieved at every location. Data values are colour-coded so as to present the information in the simplest possible graphical form.

Figure 6: Calculation of the compaction increase ΔkB

3.2 Data interpretation and continuous compaction control The difference of stiffness ΔkB and the measured absolute kB values clearly establish compaction conditions at the site during the construction process. Steps necessary to improving the soil, or halting compaction, are taken on a job-integrated basis during the initial roller passes. Table 1, in association with the figure, provides a summary of basic evaluation variants when using GPS based compaction or compaction process control. Table 1: Compactibility according to compaction measurement values

Compactibility: good Increasing the number of passes: Ï increasing Ï • Stiffness kB • Increase/change ΔkB ⇑ high Assessment: Good Compaction

Not compactable

Still compacted

→ poor kB-values ⇒ ~ 0, no increase Problem area

Î high kB-values ⇒ 0, no changes Still existing road


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Next to full-surface dynamic compaction control (so called Continuous Compaction Control, CCC), GPS based CCC of the kind used in practice with ACEplus offers compaction process control and process management in one. Logging and a job-integrated display of the compaction process are particularly helpful aids to simplifying the task for the machine driver. As well as providing a very good overview and an immediate check on the effectiveness of compaction activity, graphic visualisation of the roller driver’s effect facilitates a new quality of work and greatly enhances his job. In soil compaction, it is important to follow correct procedure for the compaction process, and correlate the machine with traditional compaction test methods at the outset of construction. Once calibrated, the machine can thus be used not only as a compactor, but as a testing machine too. Soil compaction provides the foundation for the asphalt road surface that is subsequently laid on top, so it has to meet the necessary quality requirements. The first step in asphalt compaction is usually a check-up on the soil compaction performed earlier. Adequately high and homogenous stiffness kB are prerequisites for successful compaction of the asphalt layer. The underlying soil must be capable of acting as an abutment for the first asphalt layer.

Figure 7: Overview over the compaction process, focused on the position (xi, yi)

In order to analyse the construction site with all its layers, the view may be changed to a virtual drilling core. Here, the various layers at a given location (xi, yi) can be analysed over time, i.e. the number of roller passes. The result, shown in figure 7, is a three-dimensional rendering of compaction history at that location. The target stiffness value kB|Target rises with increasing layer thickness; the required number of roller passes may vary. Measured values from the roller are calibrated against a traditional method such as a plate bearing test. The paver/finisher goes onto the tested plane surface. The paver/finisher distributes the mixed asphalt and ensures the subsequent road surface geometry through geometric movement of the screed. A combined DGPS/laser system is capable of achieving height precision in millimetres. The vibrating screed simultaneously compacts the mixed asphalt. The asphalt rollers following behind perform the main compaction by vibratory means. Measuring the paving stiffness kB indicates the increase in compaction. Simultaneous measurement of the asphalt surface temperature (infrared measurement principle) monitors the optimal compaction temperature of


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the paving and limits the zone where stiffness measurement is valid. kB measurements must be performed on paving within a temperature range of TO>T>TU, where the bitumen exhibits fluid-like behaviour and the measured stiffness is directly proportional to the density of contact points within the mineral mixture. Only under these conditions is increasing stiffness kB also a measure of increasing compaction. Other aspects of the compaction process are determined in a manner analogous to the soil compaction already described. Figure 8 shows an asphalt construction site including a paver with pre-compacting screed and a tandem asphalt roller to perform the main compaction. The paver screed width in turn determines the optimal rolling pattern for the roller driver. This rolling pattern may be specified in GPS terms, with job-integrated monitoring to verify that it is performed. Figure 8 shows a typical machine control response, along with anticipated kB stiffness and surface temperature T.

Figure 8: Asphalt compaction; compaction measurement & control and the rolling pattern

As figure 8 shows, compaction information is contained partly in the paver and partly in the roller, because the compaction process is distributed between both machines. The greater the pre-compaction at the paver, the less main compaction work there is for the roller to do, and vice versa. This, plus the fact that paver screed geometry and the paver speed dictate the rolling pattern and the rolling speed required, making a case for an online connection between the paver and the roller. This connection must be capable of exchanging machine data between all of the machines involved and displaying it fast and in real time to all concerned. This is essential to an optimal overall compaction process. With soil compaction, it should be possible to upload job site data wirelessly into the machine, and download process data from it. In contrast to asphalt compaction, this need not be a real-time process; it is possible for data exchange to occur only when the machines are not in operation, see for example the description in patent WO 2006/099772 A1 “System for Co-ordinated Soil-Cultivation”.


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CONCLUSIONS

GPS based compaction technology with tandem and single drum rollers in asphalt and soil compaction make compaction machinery easier to use in practice, which brings user benefits as follows: • Automatic regulation of roller vibration parameters • Job-integrated measurement of kB stiffness as an adequate indicator of compaction in soil compaction, supplemented by temperature measurement at the paving surface in asphalt compaction • Straightforward calibration of measured values from the rollers using a traditional compaction measurement method, like a plate bearing test • Graphic visualisation of the compaction process • A simple process display enables a driver to optimally deploy his machine (one picture says more than a thousand words) • Automatic data logging (at second intervals). Logged data is retained in the event of a power failure. The future development of GPS-based compaction technology might be driven by its application on the job. Especially the Internet working of machinery, online data exchange helps the operators on different rollers on one job site to optimise their tasks. The distinction between good and poor compaction will be supported by image recognition and image processing as the next step. In addition to today’s technologies, new possible technologies for image processing systems may take place: infrared thermal imaging camera, image recognition (contiguous unsatisfactory values = bad spot, distributed unsatisfactory values = variation, asphalt compaction algorithms, soil compaction algorithms, soil stabilisation specialities, …). Image processing is constrained for the purposes of GPS-based compaction control and guidance. Process control may provide the opportunity for modifying parameters via image processing technologies, on the basis of measured values.

REFERENCES Books: SCHMIDT, G., TONDL, A.: Non-Linear Vibrations. Cambridge University Press, Cambridge, 1986. THOMPSON, J. M. T., STEWART, H. B.: Nonlinear Dynamics and Chaos. John Wiley & Sons, Ltd., Chichester, 2002 ANDEREGG, R.: Nichtlineare Schwingungen bei dynamischen Bodenverdichtern. FortschrittBerichte VDI, Reihe 4, VDI-Verlag GmbH, Düsseldorf, 1998. BRANDL, H., ADAM, D.: Flächendeckende Dynamische Verdichtungskontrolle (FDVK) mit Vibrationswalzen. Bundesministerium für Verkehr, Innovation und Technologie, Strassenforschung Heft 506, Wien, 2000. HOFMANN-WELLENHOFF, B., LICHTENEGGER, H., COLLINS, J.: GPS, Theory and Practice. 4., revised edition, Springer-Verlag, Wien, New York, 1997. KAUFMANN, K.: Mehr Verdichtungsleistung mit bifrequenter Schwingungserzeugung. Diplomarbeit, Berner Fachhochschule HTI, Burgdorf, 2006. MANSFELD, W.: Satellitenortung und Navigation, Grundlagen und Anwendung globaler Satellitennavigationssysteme. Vieweg Verlag, Braunschweig, 1998


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Journal articles: ADAM, D., KOPF, F.: Flächendeckende Dynamische Verdichtungskontrolle (FDVK), Kalibrierung und Anwendung gemäss RVS 8S.02.6. Österreichische Ingenieur- und Architekten-Zeitschrift (ÖIAZ), 150. Jg., Heft 4-5/2005, p. 162-173, 2005. ANDEREGG, R., VON FELTEN, D.: Nonlinear Dynamic of Compaction Equipment – an Overview (in German). Österreichische Ingenieur- und Architekten-Zeitschrift (ÖIAZ), 150. Jg., Heft 4-5/2005, p. 145-149, 2005. ANDEREGG, R., KAUFMANN, K., VON FELTEN, D.: Intelligent Compaction Monitoring Using Intelligent Soil Compactors. Proceedings of the GeoCongress 2006 “Sensing Methods and Devices”, American Society of Civil Engineers ASCE, Atlanta, 2006 KAUFMANN, K., ANDEREGG, R.: Geregelte Walzenzüge und die Flächendeckende Dynamische Verdichtungskontrolle (FDVK), Teil II. Strassen- und Tiefbau, 56. Jg. Heft 9/2002, p. 12-17, 2002. MOONEY, M. A., RINEHART, R. V.: Field Monitoring of Roller Vibration during Compaction of Subgrade Soil. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, p. 257-265, 2007. Patents: WO 2006/099772 A1

System for Co-ordinated Soil-Cultivation

Links: http://www.ammann-group.ch, last accessed on April 13, 2008

* Kuno Kaufmann, Ammann Switzerland Ltd, Research & Development, Eisenbahnstrasse 44, CH4900 Langenthal, Switzerland. ** Dr. Roland Anderegg, Ammann Switzerland Ltd, Research & Development, Eisenbahnstrasse 44, CH-4900 Langenthal, Switzerland.