Study On Calculation Of Seismic Earth Pressure And Stability Problem Complex Conditions

Earth pressure refers to the lateral force acting on buildings or structures from the soil. It is the main calculation object for the engineering design of building foundations, slopes, retaining walls, offshore wharf, traffic subgrade, bridge pier and tunnel excavation, as well as the most basic and important research problem of geotechnical engineering. With the improvement of the domestic seismic design requirements, the researchers have been paying increasing attentions to the seismic earth pressure calculation increasingly. Although the theoretical and experimental studies on seismic earth pressure have so far achieved fruitful results, the research of some special conditions is still insufficient. Thereupon, based on the limit equilibrium analysis, the research on the calculation of seismic earth pressure and seismic stability in complicated conditions is presented in this study. The principal contents and achievements of this study are listed as follows:(1) The lateral earth pressure coefficients of active and passive states with the influences of soil arch are derived focused on the rigid retaining wall in translational mode. The derivation considers the circular arch of the minor principal stress and the major principal stress caused by the soil arch effects on active limit state and passive limit state, respectively. By combining the pseudo-static method and the horizontal layer analysis, the calculation methods of seismic earth pressure is improved, also the expressions of active and passive earth pressure distribution and the resultant force point are established. Then the implicit equations are generated by combining the stress analysis of soil mass and the static equilibrium of horizontal layers, which considers the principal stress deflection caused by the soil arch effect and the horizontal shear between layers. The iterative algorithm is used to calculate the slip surface shape, the earth pressure distribution and the resultant force point. The parametric discussion is taken to study the influences of soil friction angle, wall friction angle and seismic acceleration coefficients on the seismic earth pressure. Afterwards, the results are compared with the Mononobe-Okabe method in order to preliminary verify the rationality and validity of the presented method.(2) By using horizontal layer analysis, the arbitrary displacement mode is expressed with the displacement parameter and the equivalent internal friction angle, which depend on the soil stress changes of the horizontal backfill layer behind retaining wall in different displacement modes. The calculation models of seismic active and passive earth pressure in arbitrary displacement modes are established based on the pseudo-static method. The material and earthquake parameters are discussed to analyze their influence on the earth pressure in various displacement modes. Then the relationship between the friction angles and the displacement of the retaining wall is set up based on the model test results. The calculation method of seismic earth pressures in non-limit state considering the displacement effects is proposed by adopting a means analogous to the earth pressure in limit state. After that, the parameters of the earth pressure distribution and the resultant force point are discussed to analyze the influence of displacement modes and states on earth pressure. The results by the presented work are also compared with those of the previous research.(3) An improved pseudo-dynamic method, considering the seismic amplification effect, is proposed to calculate the seismic active earth pressure on submerged retaining wall with inclined back. Similarly, the seismic passive earth pressure on submerged wall with vertical back is also studied. Then the parametric discussion is taken. In addition, based on limit equilibrium analysis, the seismic active earth pressure under vertical and two-dimensional steady seepage, as well as the seismic passive earth pressure with two-dimensional steady seepage are calculated by pseudo-dynamic method, respectively. This computation takes the pore pressure induced by seepage and earthquake into consideration. The modified earth pressure coefficients including seepage effects are derived. And the parametric study is taken on the slip surface and the earth pressure, the modified passive earth pressure coefficients are analyzed in pseudo-dynamic way.(4) A formula of stability safe factors of wall retaining dry backfill against sliding and overturning under seismic action is presented by pseudo-dynamic method. The derivation includes the influence of seismic amplification factors, wall back inclination and backfill surface inclination. The effects of various parameters on seismic safe factors are explored. The results are then compared with those by pseudo-dynamic method. Afterward, the backfill is categorised into two extreme conditions as’free water’and’restrained water’ according to soil permeability. Based on pseudo-static method, a reasonable approach is proposed to calculate the seismic stability of waterfront retaining wall against sliding and overturning in partial submerged condition. This method considers the excess pore pressure and the dynamic water pressure caused by earthquake and the buoyance at the bottom of retaining wall. The form of slip surface, either straight line or polyline, is assumed according to the modulus difference of the reinforced bar for retaining wall. The expression of tensile force coefficient for reinforced bar in partial submerged condition is derived by using horizontal layer analysis and pseudo-static method. The contrast between’free water’ condition and’restrained water’condition is described in the two forms of slip surface.