Study On Active Earth Pressure Of Unsaturated Soils And Overturning Stability Of A Retaining Wall

With the state ’s large investment in infrastructure construction,there are a large number of retaining wall projects in the construction of water conservancy projects,highways,railways,housing construction and bridge projects.The destruction of retaining walls under earthquake seriously threatens people ’s lives and economic development.Seismic active earth pressure is the main load of seismic design of retaining wall in high intensity area.The water level behind the wall,soil cracks and soil mechanical properties all affect the determination of seismic earth pressure of retaining wall.Considering the influence of soil arching effect in the earth pressure problem,the results will be closer to reality.At the same time,the overturning stability of retaining wall under earthquake is also an important part of retaining wall checking.Therefore,based on the principle of pseudo-dynamic method,pseudo-static method and unsaturated soil mechanics,this paper first proposes the calculation formula of seismic active earth pressure of retaining wall under high/medium/low water level according to the relative position relationship between water level,crack depth and wall heel.Then,under the condition of low water level,the calculation formula of seismic active earth pressure considering soil arch interlayer shear and the calculation formula of anti-overturning stability coefficient and overturning displacement of unsaturated soil retaining wall under earthquake are derived respectively.Then,the application steps of the results are given and the correctness and applicability are verified by comparing the literature formulas and field test data.Finally,the influencing factors are analyzed.The main research contents and conclusions are as follows:(1)Considering the comprehensive influence of water level change,seismic action and unsaturated characteristics of soil,three mechanical models for seismic active earth pressure analysis of unsaturated soil retaining wall with cracks under high/medium/low water level are proposed.Based on the pseudo-dynamic method,the seismic active earth pressure solution of inclined retaining wall under water level change is established.It is concluded that the seismic active earth pressure is significantly affected by water level,crack depth,matric suction and its distribution and suction angle.Engineering measures are needed to maintain the stability of matric suction and its distribution,low water level and small crack depth to optimize the seismic design of retaining wall.(2)Considering the influence of soil arching effect and interlaminar shear effect,seismic action and unsaturated characteristics of soil,the solution of seismic active earth pressure considering soil arching shear under low water level is derived based on quasi-static method and horizontal layer analysis method.It is concluded that soil arching effect and interlaminar shear effect affect the distribution of seismic active earth pressure,the moment of resultant force around wall heel and the action point of resultant force.(3)Considering the seismic action and the unsaturated characteristics of soil,the anti-overturning stability coefficient and overturning displacement of the anticline retaining wall under low water level earthquake are derived based on the pseudo-dynamic method.It is concluded that the seismic coefficient,matrix suction and distribution,suction angle and retaining wall inclination angle have significant effects on the overturning stability coefficient and overturning displacement.(4)The obtained seismic active earth pressure formula can reasonably reflect the influence of water level,soil arching effect,interlaminar shear effect and unsaturated soil characteristics,which makes the earth pressure calculation model more accurate in theory.On this basis,it is extended to the study of overturning stability of retaining wall.The results are in good agreement with the theoretical solutions and experimental data in the literature.When some parameters are adjusted,it can be simplified into the existing formula.