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Unformatted text preview: 1. DEFINITION OF THE PROBLEM A sensitivity study using SHAKE91; a computer program which computes the response of a semi-infinite horizontally layered soil deposit overlying a uniform half- space subjected to vertically propagating shear waves is requested. SHAKE 91 makes the analysis in the frequency domain, and, therefore, for any set of properties it is a linear analysis. An iterative procedure (equivalent linear model) is used to account for the nonlinear behaviour of the soils. For detailed information and assumptions of the model, the reader is advised to refer to SHAKE 91 Users Manual. Sensitivity study will be made by conducting runs with different soil profiles and characteristics, and the observed difference will be reported. II. SETS OF RUNS TO ACHIEVE THE SOLUTION The soil profile is given as generic 30m deep soil deposit with average dynamic properties (V s =170-350 m/s, PI=15) with provided Adapazar rock motion scaled to 0.25g. First, soil profile is idealised as a single layer, then consisting of 3 and 6 sublayers respectively, excluding the last sublayer; the bedrock in each case. Soil profiles are shown below: Figure 1: Idealised soil profile types (by number of sublayers). A total of 11 runs are planned to make the sensitivity analysis. These are summarised in Table 1 as follows: SOIL PROFILE NO. VS PI RUN 00 1 170 m/s 15 RUN 01 2 170 m/s 15 RUN 02 3 170 m/s 15 RUN 03 2 260 m/s 15 RUN 04 2 350 m/s 15 RUN 05 3 260 m/s 15 RUN 06 3 350 m/s 15 RUN 07 2 170,260,350 m/s (linearly increasing with depth) 15 RUN 08 3 170,206,242,278, 314,350 m/s (linearly increasing with depth) 15 RUN 09 2 170 m/s RUN 10 2 170 m/s 30 Table 1: List and general classification of SHAKE 91 runs. As can be observed in Fig 1 and Table 1 respectively, Runs 00, 01 and 02 are used for sensitivity analysis of the number of sublayers introduced in the input file. Different calculations are performed using different numbers of sublayers for the same soil type, having the same dynamic properties and plasticity index, throughout the depth. Therefore, results of the first three runs with controlled properties will yield the effect of subdivision of layers on the acceleration response. Runs 03, 04, 05 and 06 are made and plotted on the same graph so as to observe the effect of different shear wave velocities in the profiles. Meanwhile, it will be possible to observe if there is a considerable amount of divergence in the values in case of different number of sublayers. It may also be said that Runs 03, 04, 05 and 06 are somewhat extensions of the first sublayers....
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- Fall '06