An Improved Quasi-dynamic Method For Seismic Earth Pressure Considering Displacement Effect

Nowadays,in seismic design of retaining wall in the specification,the seismic earth pressure calculation theory is still using the pseudo-static method,but the pseudo-static method cannot consider the time effect of seismic action and the effect of the phase.Pseudo dynamic method can be a very good make up for the defect of pseudo-static method,but the current study of pseudo dynamic method mainly based on the limit state,on the no-limit state of the research of the seismic earth pressure is still inadequate.The displacement mode of retaining wall has a great influence on the seismic earth pressure of retaining wall,and the research on the non-limit seismic earth pressure based on the quasi-dynamic method considering the displacement mode of retaining wall is insufficient.Therefore,this paper,based on the conclusions of previous experimental studies and the pseudo-dynamic method and horizontal layer analysis method,studies the calculation theory of non-limit seismic earth pressure of retaining wall under different displacement modes.The main research work of this paper is as follows:(1)Taking the rigid retaining wall under earthquake load as the research object,considering the influence of RB and RT displacement modes of retaining wall on the play value of friction Angle,the friction Angle is expressed as the function related to the displacement amount and position height of retaining wall,and the calculation expressions of non-limiting active earth pressure and resultant force acting point of retaining wall under RB and RT modes are derived.According to the difference of the maximum displacement of the top of the wall and bottom of the wall,the calculation model can be divided into two non-limit state conditions,which can describe the different non-limit state conditions in which the friction Angle gradually develops along the height of the wall,and the relationship between displacement of retaining wall,seismic load and earth pressure is established.The calculated results are compared with the experimental results,and the rationality of the method is verified.The influence of the top displacement(RB mode)and bottom displacement(RT mode)and seismic dynamic parameters on the distribution of earth pressure,the degree of friction Angle,the resultant earth pressure and the resultant point of earth pressure were discussed.The results show that under the assumption of sinusoidal vibration,the strength of lateral earth pressure also changes sinusoidal form with the vibration time,and the period is consistent with the seismic period,but the amplitude of strength fluctuation is different at different height of retaining wall.Under RB mode,the earth pressure gradually decreases with the increase of retaining wall displacement until reaching the active limit state.The greater the displacement of the retaining wall,the lower the height of the resultant point of action.For the earth pressure in the RT model,the effect of seismic action is mainly located in the middle and upper part of the curve.The effect of displacement of retaining wall on resultant force is relatively small.The larger the displacement of retaining wall,the higher the resultant point of earth pressure.(2)For the rigid retaining wall with T-displacement mode,considering the change of friction Angle with displacement of retaining wall under active and passive state,the distribution of friction Angle along the height of retaining wall is expressed as a function,and an improved quasi-dynamic method is established to calculate the non-limiting active and passive earth pressure under T-displacement mode of retaining wall.The combined forces of active and passive earth pressures and the expressions of the combined forces are derived.The rationality is verified by the previous experimental data and calculation theory.The effects of vibration time,displacement of retaining wall,seismic acceleration parameters and soil friction Angle on active earth pressure distribution,resultant force and height of resultant force are discussed.The results show that the variation of lateral earth pressure intensity with vibration time under active and passive conditions is similar to the RB and RT displacement modes.Under the active state,the earth pressure gradually decreases with the increase of retaining wall displacement until reaching the active limit state.The greater the displacement of the retaining wall,the higher the height of the resultant point of action.For the earth pressure under passive state,the earth pressure increases gradually with the displacement of retaining wall,until reaching the passive limit state.The larger the displacement of retaining wall,the lower the resultant point of earth pressure.