Seismic Site Response of 1-D Inhomogeneous Ground with Continuous Variation of Soil Properties

Abstract

The main objective of this thesis is to enhance the scope and response estimation ability of routine one dimensional (1D) seismic response analysis in frequency domain using equivalent linear (EQL) method. This is the popularly used method of analysis in engineering practice. For this purpose a computer program is developed incorporating the scheme to accommodate the objectives of this research work. In order to meet the solution procedure employed in the routine analysis, the soil deposits exhibiting continuous inhomogeneity are also being idealised as layered systems. The analytical results obtained for continuously inhomogeneous soil deposits have demonstrated that the layered idealisation of such soil deposits would result in contradictory response quantities. Secondly, the major limitation of the EQL method is inconsistent estimation of response at high frequency and in the resonant frequency region. This may be attributed to the use of single valued strain in all the frequency ranges during the iterations of EQL scheme of analysis. Both these drawbacks of the popularly used computer programs have been addressed and modifications are implemented in the computer program developed as part of this research work. The numerical procedure developed and implemented in the computer program is capable of handling all possible cases of idealisation of soil deposit. Two modifications have been proposed to routine EQL analysis scheme; one with respect to computation of effective strain in the iterative process and secondly, frequency dependent damping model is formulated to overcome inconsistencies in predicted response at certain frequency ranges. The results are compared with both analytical solutions and observed data of geotechnical downhole array sites of Japan and USA. Finally an alternative method is proposed to estimate the fundamental period of the layered deposit by approximating it with linearly varying shear wave velocity profile. The outcome of this research work is expected to enhance the predictive capabilities of the most commonly used site response analysis procedure and contribute in the direction of improving the seismic site response analysis in engineering practice.