15 Evaluation of Seismic Performance of an Excavation Support System 143 Fig. 15.3 Instrumentation plan of cut and cover tunnel construction between Belediye and Mecidiye stations Fig. 15.4 Geometry and structural elements of bracing system Fig. 15.5 3D finite element model of cut-cover tunnel excavation (a) first stage and (b) last stage piles and tie-back anchors (Fig. 15.4). A typical finite element model showing excavation area, structures of support system, adjacent buildings is shown in Fig. 15.5. Settlements and lateral movements were investigated to evaluate the performance of support system, in order to be in the desired deformation range under static and seismic loads. Static loads are consisted of lateral earth pressure and overburden load caused by adjacent buildings. To model the soil, ten node wedge elements were used. Various element sizes ranging from very fine to very coarse were used during calculations. Coarse size elements were selected due to efficiency of calculation of time in regards to change at results. The soil was modelled with Mohr-Coulomb failure criterion approximated to be a linear elastic-perfectly plastic. The constitutive model used to simulate the soil behavior required five basic input parameters and two seismic parameters shown in Table 15.1: the Elastic modulus (E), Poisson’s ratio (¤) (0,2), cohesion (c), friction angle (¥), unit weight (”), shear modulus (G) and shear velocity (Vs).
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