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Synopsis: Development of tomography- surface wave analysis for engineering assessment of geotechnical structures

August 2007
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Synopsis: Development of tomography- surface wave analysis for engineering assessment of geotechnical structures

The research has been funded by The Ministry of Science, Technology and Innovation, Malaysia under Science Fund No.01-01-02-SF0338

prepared by Geotechnical Engineering and Soil Dynamics Research Group (GESID), Universiti Kebangsaan Malaysia

Principal Investigator: Zamri Chik, Mohd.Raihan Taha, Amiruddin Ismail, Mohd.Marzuki Mustafa, Sri Atmaja P.Rosyidi.

 Investigator: Khairul Anuar Mohd.Nayan, Anuar Kasa

 

Introduction

Our staff of LATEI, Sri Atmaja has already joined in the research team of GESID-UKM, has been successful to goal the research project together with other members of GESID. The research is started from 1st October 2007 and will be finished 18 months after the date mentioned above. He has an important rule in the research for conducting the main stage of research and coordinating the technical team in the research.  Some important information from the research project are described below.

Specific objective of the project:

1.       To characterize the soil dynamic properties such as the shear modulus reduction curve and the soil-structure interaction of Malaysian residual soil using surface wave analysis.

2.       To develop an advanced processing of surface wave measurement in order to determine in-situ the material dynamic stiffness (in terms of soil bearing capacity), depth profile, attenuation   properties and damping ratio for geotechnical  structures design, such as lining of tunnels, soil nails, rock achors, embankment and subgrade underlaying a pavement layers.

 3.       To develop a software of tomographic surface wave analysis from the above processing for geotechnical structural evaluation purposes. 

Literature review summary

Shear modulus and damping ratio of geotechnical materials are an important parameter in characterizing the mechanical behavior of these materials under many different types of loading for design of foundation structures and constructions of civil infrastructures.  These soil parameters are used in dynamic soil-structure interaction analysis for small-strain problems (below 10-3 percent) such as machine foundations and as reference level for larger-strain problems (10-3 to 10-1 percent) such as potential liquefaction during earthquake shaking or blasting force and for in situ evaluation of hard-sample deposits.  For accurately providing these parameters for dynamic structural design, the interrelationship between shear modulus, damping ratio with state of stress and strain level is required.   Shear wave velocity is directly related to the stiffness of the material skeleton through which the shear waves propagate.  It is possible to measure shear wave velocity and then derive material parameters such as shear modulus or infer material parameters such as in situ density, from measured wave velocity.  The behavior of shear modulus and its related strains of soils can be obtained from field testing or laboratory measurement.   Laboratory tests such as cyclic triaxial, resonant column, cyclic simple shear and cyclic torsional shear, have been used.  However, if natural deposits are to be tested, the laboratory devices have the shortcomings of using samples that are somewhat disturbed and of having the difficulty of properly simulating in situ stress conditions.  Therefore, the laboratory measurements need to confine and consolidate the soil sample back to the state of stress to replicate field condition.  The effective measurement of in situ shear modulus can be obtained with in situ seismic methods.  The methods have the advantage that the state of stress is inherently included in the measurement procedure.  The actual field condition of actual effective stress and drainage condition of undisturbed soil can be measured.  In addition, the average stiffness condition of material which describes the inhomogeneity media can be directly assessed with propagation of seismic waves between active source and receivers (Luna & Jadi 2000).   The in situ seismic methods most often used today are the crosshole and downhole.  These methods require the installation of one or more boreholes where the installation is generally time consuming and costly.  The surface wave methods, on other hand, involve measurement of propagation of surface wave to evaluate shear wave velocity and shear modulus profile.  The surface wave methods consists of the spectral-analysis-of-surface-wave (SASW), continuous surface wave (CSW) and multi-channel spectrum analysis of surface wave (MSASW) method which differences between those methods are in the source type and amount of receivers.  In the surface wave methods, both source and receivers are placed on the ground surface.  Surface wave are generated by applying vertical loading on the ground surface.  The propagation of these waves along the surface is then monitored and the stiffness profile of the site is typically calculated through a forward modeling or inversion process of surface wave propagation.  The surface wave method is non intrusive method because of no borehole required, cost effective and especially well suited for in situ testing of hard to sample soils.  Many researchers have carried out the study of surface wave method in different applications such as characterization of foundation (Madshus & Westerdahl, 1990; Stokoe et al. 1994), detection of soil profile (Matthews et al., 1996), evaluation of concrete structures (Rix et al., 1990), detection of anomalies (Gucunski, 2000), assessing compaction of fills (Kim et al., 2001) and the evaluation of railway ballast (Zagyapan & Fairfield, 2002).  Study on direct signal processing of multi waveform of surface waves from in situ measurement to produce the geotechnical properties of seismic wave attenuation and damping ratio of soils structure has been initiated by Lai and Rix (1998).

Related research

Although the surface wave method using the SASW technique has been proven as an effective method for site characterization (Stokoe et al., 1994), the theoretical analysis of signals of surface wave dispersion should be continued to improve the accuracy of the method and more automation of the analysis procedures, and also as simple tool for geotechnical engineers.   In the case of seismic surface waveforms are, by their very nature, transient, usually non-stationary events. The advanced study of signal processing of seismic surface wave was started by Zywicki (1999).  Advanced signal and spatial array processing method was employed to solve the most acute problems associated with traditional geotechnical surface wave analysis.  Other related research has been using the wavelets analysis which Haigh et al. (2002) started to conduct the study of characteristics of non–stationary pattern of surface waves from the earthquake recording.  From his study, it was found that the harmonic wavelets analysis is to be useful tool for the analysis of non-stationary signals and generate the visualization analysis of combining the time-histories and Fourier transform which give great help in interpreting the behavior of geotechnical structures under earthquake loading.  In other side, Santamarina (1994) introduced the fundamental aspect of wave propagation in geomaterials and followed by and introduction to the tomographic inversion.  His study showed the classical algorithms and algebraic solution for tomographic analysis based on Fourier analysis.  Developed from fundamental of wave propagation in geomaterial, the multi-waveform of seismic surface wave is also useful in order characterize the attenuation and damping ratio (Lai, 1998; Lai & Rix, 1998; Rix et al., 2000).  In their studies, an attenuation curve was constructed from the observed spatial attenuation of Rayleigh wave amplitudes and then was inverted to obtain the material shear damping ratio.  The analytical procedures which they used to obtain the shear wave velocity and damping ratio profile were performed separately.  However, studies on the integrated surface wave analysis and its tomography interpretation for simultaneously generating the shear modulus and damping ratio profile of geotechnical structures were relatively few.  In this study, the advanced processing of surface wave tomography will be employed in order to characterize dynamic soil properties for geotechnical applications.  The wavelets and Fourier of continuous and discrete transform will be used to decompose and construct the better surface waveform and provide a convenient format for modeling, analysis and simulation of geotechnical properties. 

References : 

Gucunski, N., 2000, Field Implementation of Surface Waves for Obstacle Detection (SWOD) Method, Proc. of 15th World Conference of Non Destructive Testing, Rome, Italy.

Haigh, S.K., Teymur, B., Madabhusi, S.P.G. & Newland, D.E., 2002. Application of wavelet analysis to the investigation of the dynamic behaviour of geotechnical structures, Soil Dynamic and Earthquake Engineering 22 (2002), Elsevier Science, pp.995-1005.

Kim, D.S, Shin M.K and Park H.C., 2001, Evaluation of density in layer compaction using SASW method, Soil Dynamic and Earthquake Engineering 21 (2001), Elsevier Science, pp.39-46.

Lai, C.G. & Rix, G.J., 1998. Simultenuous inversion of Rayleigh phase velocity and attenuation for near-surface site characterization. Research Report. Georgia Institute of Technology, US.

Lai, C.G. 1998. Simultaneous inversion of Rayleigh phase velocity and attenuation for near-surface site characteri-zation. PhD. dissertation. Georgia Institute of Technology.

Madshus, C., & Westerdahl, H., 1990. Surface wave measurements for construction control and maintenance planning of roads and airfields. Proc.of 3rd. Int. Conf. On Bearing Capacity of Roads and Airfields, July 3-5, Trondheim, Norway.

Matthews, M.C., Hope, V.S. & Clayton, R.I., 1996. The geotechnical value of ground stiffness determined using seismic methods. In Proc. 30th Annual Conf. of the Eng. Group of the Geol. Soc., University of Lige, Belgium.

Rix, G.J., Bay, J.A, & Stokoe II, K.H., 1990. Assessing in situ stiffness of curing Portland cement concrete with seismic tests. Paper presented to Annual Meeting, Transportation Research Board, Washington, D.C., January.

Rix, G.J., Lai, C.G.& Spang, A.W., Jr. 2000. In situ measurement of damping ratio using surface waves. Journal of Geotechnical and Geoenvironmental Engineering 126(5): 472 – 480.

Santamarina, J.C., 1994. An introduction to geotomography. Geotechnical characterization of sites, R.D. Wood, ed., Oxford and IBH Publishing Co., New Delhi, India, 35-43.

Stokoe II, K.H., Wright, S.G., Bay, J.A, & Roesset, J.M., 1994. Characterization of geotechnical sites by SASW method. Geotechnical characterization of sites, R.D. Wood, ed., Oxford and IBH Publishing Co., New Delhi, India, 15-26.

Zagyapan, M. & Fairfield, C.A., 2002, Continuous surface wave and impact methods of measuring the stiffness and density of railway ballast, NDT&E International 35 (2002), Elsevier Science,pp.75-81

Zywicki, D.J. 1999. Advanced signal processing methods applied to engineering analysis of seismic surface waves. PhD. dissertation. Georgia Institute of Technology.


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