Simplified Analysis Of Site Amplification Effects For Liquefiable Deposits And Comparative Study On Ground Motion Intensity Measures

Strong earthquakes happened more frequently in recent years all over the world, resulting serious destructive disaster phenomena, among which the liquefaction problem is an outstanding issue, increasing the accuracy of liquefaction hazard evaluation is an important way to minimize the damage caused by the liquefaction, so study the liquefaction hazard evaluation will be of geart significance. The accuracy of liquefaction hazard evalutions depends on the calculation accuracy of the ground motion intensity measures and the correlation between the liquefaction hazard and the ground motion intensity measures. On one hand, the site amplification effects plays an important role in calculating the ground motion intensity measures in arbitary depth of the soil. But the accuracy of the site amplification effects used now is not enough, also the parameters chosen and using the site response analysis software is too complicated for engineers, so it’s important to bulid up a relative high accuracy and easily useful simplified analysis method of site amplification effects for enigeers. On the other hand, CSR, the ground motion intensity measures often used now, leading significant differences between the evalution and the actual hazard situation in some cases, so it’s necessary to compare the ability of different ground motion intensity measures to evaluate the liquefaction hazard, and then choose the optimal ground motion intensity measure to evaluate the liquefaction hazard.The reaserch pays attention to the problems list above, according to the transfer function of a uniform layer of isotropic, kelvin-voit damped soil overlying rigid rock excited by harmonic horizontal motion and considered nonlinear effects impacted on the soil shear stiffness which is caused by the shear strain and excess pore water pressure, proposed an amplification formula for liquefiable deposits which is more clearly in physic significance. Conducted a series of centrifuge shaking tests to verify the correctness of the simplified amplification formula, compared the ability of different ground motion intensity measures to evaluate liquefaction hazard, established a simple method of site amplification effects which is easily to use for engineers. The topics and innovativeness in the study are listed below:(1) Used the shear strain and excess pore water pressure ratio to updated the one dimensional wave theory of a uniform layer of isotropic, kelvin-voit damped soil overlying rigid rock/elastic rock excited by harmonic horizontal motion, and then established the depth reduction coefficient curves of different ground motion intensity measures according the updated formula;(2) Conducted six sets of centrifuge model tests differ from soil types, soil thickness and input waveforms and validated the updated formula computed values is consistent with the actual amplification ratio and more closely to the actual amplification ratio compared to the non-updated formula computed values on the condition that lower midrange, small earthquake, soil thickness is less than 30 m.(3) Proposed the ground motion intensity measures calculation method in arbitrary depth according to the ground motion intensity measures calculation method based on the shaking table and the depth reduction coefficient curves of different ground motion intensity measures, proposed a new method to normalize the effects of different relative density impacted on the pressure and the settlement of different shakeing events, also analyized the correlation between different ground motion intensity measures and liquefaction hazard according to the ground motion intensity measures calculation model based on the centrifuge shaking table; and their analyized the anti-liquefaction strength expressed by different ground motion intensity measures according from the relations between the calculated surface intensity measures and the hazard;(4) For in-situ site, proposed a method to calculate the average shear strain rAA and the maximum depth-averaged excess pore water pressure ratio ru,max within the near-surface 30 m, and then calculated the amplification effects of six earthquake recordings of treasure island downhole array to validate the efficience and simplicity when using the updated formula to analysis in-situ sites amplification effects.