Study On Seismic Dynamic Characteristics And Seismic Design Of Multistage Retaining Structures And Slopes

Based on the Project of Study on Seismic Design Method of Special Retaining Structures in High and Steep Slopes (No.2008G028-D) supported by the Ministry of Railway, seismic dynamic response characteristics and seismic design methods of multistage retaining structures and slopes in Dali-Ruili Railway were studied. Based on series of large-scale shaking table tests, seismic dynamic response characteristics of multistage retaining structures of bedrock and overburden layer slopes and consequent rock slopes were studied systematically, numerical models were established and the model tests of Wenchuan earthquake XZ-excitation conditions were simulated. The seismic displacement modes and its characteristics under earthquake loadings were discussed according to the displacement response data of model tests. The upper bound theorem of limit analysis and strength reduction technique based on pseudo-static method, seismic earth pressures of retaining walls in multistage slopes were analysed, and the study on seismic dynamic stability of the multistage retaining structures for high slopes and its seismic design method were conducted. The key studies are as follows:(1) Slope models design for large-scale shaking table testsThree models for bedrock and overburden layer slopes and three models for consequent rock slopes, which the geometric scale is1:8, were designed respectively. According to similarity theory, the similarity relations of the main physical quantities were studied, the main similarity coefficients and the simulation materials and its main properties of physical and mechanics for large-scale shaking table model tests were determined. Three seismic waves including Wenchuan earthquake wave, Darui synthetic seiswave and Kobe seismic wave were used in the model tests, and the excitation rules of six model tests were determined.(2) Seismic dynamic response behaviors analysisThe dynamic response behaviors of acceleration, seismic earth pressure, seismic displacement, and bolt seismic strain response under different seismic waves, its peak excitation acceleration and excitation directions were studied systematically according to three models for bedrock and overburden layer slopes and three models for consequent rock slopes respectively. According to different earth retaining structures, the comparison analysis of dynamic response characteristics of the models for bedrock and overburden layer slopes were conducted. In the study of dynamic response characteristics of earth retaining structures for consequent rock slopes, the same works but according to the rock layer angles were finished.(3) Numerical simulation about the seismic response behaviors based on the large-scale shaking table model testsNumerical models according to the plane strain problem were performed, and FLAC3D was employed based on the XZ-excitation conditions of Wenchuan seismic wave of shaking table tests. In the simulation of dynamic response characteristics of the bedrock and overburden layer slopes models, the comparison analyses were conducted between gravity retaining walls, and the results can be used as a supplement or verification for shaking table model tests. In the numerical simulation of dynamic response behaviors of models for consequent rock slopes, the comparison analyses according to the different rock layer angles were finished, and the simulation results can be used as a supplement or verification for shaking table model tests samely.(4) Study on seismic displacement modes of retaining structuresThe study of the seismic displacement modes and its characteristics of the retaining structures including gravity retaining wall, sheet-pile retaining wall, and anchor lattice frame structures were conducted according to the permanent displacement response based on three large-scale shaking table model tests of bedrock and overburden layer slopes respectively. The study indicates that the seismic displacement modes of retaining structures can be as follows:sliding or translaction mode, rotation inward or outward about base, and the coupling of the sliding to or from the filling soil mass and the rotation inward or outward about base. Moreover, the displacement magnitude, seismic displacement mode, and its behavior can be influenced not only by the exciting seiswave, excitation direction and type, peak excitation acceleration, but by the retaining structures itself and its combination. In addition, the seismic behaviors of the retaining structures were discussed on the basis of the study on seismic displacement modes.(5) Study on seismic earth pressure and seismic design method of multistage retaining structuresAccording to the upper bound theorem of limit analysis and strength reduction technique based on pseudo-static method, seismic earth pressures of multistage retaining walls were studied, and the upper bound solutions for determining seismic active and passive earth pressures were deduced. The following factors are taken into account including horizontal and vertical seismic coefficients, the angle of the retaining wall back, slope surface shape and its retaining structures, the influence of upper retaining wall on the lower, soil cohesion, adhesive strenghth between soil and retaining wall back. The propsed methods can be applied to the determination of seismic active and passive earth pressures of cohesionless and cohesive soils, and complicated slope shapes.(6) Static-dynamic stability analysis and seismic design method of multistage and combination retaining structuresThe safety factor of slope stability was directly used as the strength reduction coefficient, the seismic stability analyses of three kind of supporting types of anchored retaining walls on the high slopes were studied according to the upper bound theorem of limit analysis and strength reduction technique based on pseudo-static method. In addition, the sensitivity of the parameters was analyzed using the orthogonal analysis method, and the seismic design methods of retaining structures were studied. The seismic design methods and the suggestions for the practice were put forward through case studies.