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The effect of basin edge slope on the dynamic response of soil deposits

Cılız, Serap
The effects of basin edge slope on the dynamic response of soil deposits are assessed by using one-dimensional and two-dimensional numerical analyses. 24 basin models having trapezoidal cross section are generated to represent different geometries (basin depth, basin edge slope) and soil type. Harmonic base motions with different predominant periods (Tp) are used in the analyses. The results indicate that, for a constant basin edge slope and a constant ratio of fundamental period of site to the predominant period of base motion (Tn/Tp), the response is almost the same for different soil types, basin depths and base motions. In the sloping edge region, one-dimensional response analysis predictions are found to be conservative compared to two-dimensional analysis predictions; however beyond this region they are unconservatively biased by a factor as high as 1.5. The sloping edge region and the horizontal region of the basin are denoted by normalized distance (ND) values varying from 0 to 1 and 1 to 2 respectively. The critical region where maximum amplification observed falls in the range of ND=1.0 to ND=1.5 for basins having slopes greater than 30o. The lower boundary of the critical region is shifted towards as low as ND=0.2 for basins having slopes less than 30o. For a constant value of Tn/Tp, the increase in the amplification is smooth for basins with gentle slopes as compared to basins with steep slopes for the region where ND~1. For a basin and earthquake couple approaching to resonance state (Tn/Tp=1), the amplification for the region where ND is greater than 1 is found to be as high as 100% of that is found for the region where ND~1.