Research On The Characteristics Of Slip Surface In Backfill And The Modified Calculation Model Of Earth Pressure On Balance Weight Retaining Wall

Earth pressure is a key issue in retaining wall design,and the features of slip surfaces in backfill have a fundamental influence on the earth pressure,especially for complex wall backs such as balance weight retaining walls,where the backfill forms several slip surfaces,and the earth pressure at the back of wall needs to be calculated in sections and there are many influencing factors,so the calculation of the earth pressure is troublesome.Based on the finite element method（FEM）,the evolution of slip surfaces and the earth pressure distribution with movement of retaining wall is investigated for a balance weight retaining wall;the determining factors for the significant difference between the FEM and theoretical calculations of earth pressure are discussed and verified against centrifuge modeling tests.A modified calculation method is proposed for earth pressure against balance weight retaining wall based on the state of mobilized slip surface to address existing problems in traditional calculation models.The achievements may serve as reference for calculating earth pressure against balance weight retaining walls.The main conclusions are as follows:（1）When the backfill reaches the active limit state under translation mode,the slip surface towards the lower wall and the second slip surface towards the upper wall occurred successively,the position and the shape of the slip surface is basically consistent with the design calculation method of the code.But the first slip surface towards the upper wall assumed by the code will not be formed,which leads to deviations between the FEM value of the earth pressure and the calculated value.The approximate first slip surface towards the upper wall will be formed in the backfill under rotation mode of the wall,the FEM value of the earth pressure is closer to the calculated value.（2）The friction angle of the upper wall and the equilibrator are both small,which can be ignored,i.e.,the direction of earth pressure is perpendicular to the surface.And the lower wall basically reaches the limit friction angle,which is in line with the assumptions of the code.The action point of earth pressure on the upper wall is located near 1/3 of the upper wall height,and the point of earth pressure on equilibrator is basically stable at 0.445 times the width from the edge.However,the action point of earth pressure on the lower wall is significantly affected by the height of the embankment slope and the movement mode of the wall,and the fluctuation range is large.（3）The angle of mobilized shearing resistance on the first slip surface significantly redistributes earth pressure between the upper wall and the lower wall.When the angle of shearing resistance on the first slip surface is not fully exerted,the earth pressure generated by the slip prism is more transmitted to the second slip surface,increasing earth pressure on the upper wall and decreasing earth pressure on the lower wall,and the lower the shear angle exerts,the greater the increase and decrease.（4）A modified calculation method is proposed for earth pressure against balance weight retaining wall by introducing a coefficient of the angle of mobilized shearing resistance（η）for the first slip surface towards the upper wall.With this improvement,the characteristics of the slip surface and the distribution of the earth pressure between the upper wall and the lower wall are well reflected.The height of the embankment slope and the coefficient of movement mode have the most significant influences on the value ofη,which is determined by the functionη=1.032-0.432e^-h/2.4-0.167λ.