Geotechnical site exploration is a key component in the design process in civil engineering. Owing to the limited resources alloted to exploration programs and the natural variability of soil profiles, much of the information about the site is reliant on engineering judgment and interpolation of data available from discrete sampling of soil deposits. In recognition of such limitations, the last decade has witnessed significant advances in dynamic site characterization as a means to continuously probe large volumes of soils. Among such methods, the non-invasive seismic techniques represent particularly efficient complement to standard exploration programs. In view of the complexity of the underlying wave propagation problem, the seismic methods are typically based on approximate theoretical models that use wave velocity measurements as an input. These deficiencies, among others, can lead to multiple interpretations of experimental data, resulting in non-unique estimates of subsurface profiles.
Anjun Lu, Graduate Student Researcher
Sylvain Nintcheu, Graduate Student Researcher
99/223 |
"Full Waveform Analysis in Site and Material Characterization by Seismic Methods," B.B. Guzina and A. Lu, University of Minnesota Supercomputing Institute Research Report UMSI 99/223, November 1999. Publication in press. |
The central theme of the proposed work is the development of a novel method for non-intrusive testing of horizontally-stratified subsurface profiles. Based on the full waveform analysis of the ground surface motion, the proposed technique provides comprehensive information about the material stiffness, density, and damping of the profile tested. Method of analysis employs a rigorous three-dimensional wave propagation solution for a multi-layered viscoelastic medium. The forward model is coupled effectively with an appropriate inversion algorithm that estimates material properties of the layered medium by systematically adjusting the initial model parameters according to discrepancies between the measured and predicted records of surface displacements generated by a dynamic source. To account for the inevitable presence of noise in physical measurements and the strong non-linear dependence of measured response on the distribution of material stiffness, damping and density across the site, the method revolves around the maximum likelihood inverse theory and the modified Newton search technique. Issues such as resolution and error of the inverse solution are investigated.
In parallel with the foregoing developments, research is also being initiated to investigate the suitability of several common assumptions in seismic site characterization. In particular, emphasis is placed on analyzing the dynamic interaction between the site and the loading system (serving as a seismic source) and its effects on the measured site response.
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URL: http://www.msi.umn.edu/about/publications/annualreport/ar2000/depts/IT/CivEng/guzina.html |
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