Experimental Research On Active Earth Pressure Of Limited Cohesionless Soil Under Immersed

With the further development of urban underground space,the urban land is becoming more and more tense,and the building density gradually becomes larger.The situation that the space between the newly-founded foundation pit envelope structure and the existing underground structure of the building is too short happens from time to time.Under these circumstances,the soil between the foundation pit to be excavated and the existing building becomes limited backfill,and the traditional semi-infinite soil earth pressure theory has become no longer applicable.In addition,although the research work contains both theoretical and experimental aspects,the soil conditions studied are relatively single,and the saturated soil behind foundation pit retaining structure is not considered.The groundwater level in coastal cities in China is relatively high,and the retaining structures that are constructed are often in saturated stratum.At this time,there are impacts of hydrostatic pressure,even seepage and excess pore water pressure on soil behind retaining wall.Therefore,under hydrostatic conditions,this article takes the active earth pressure of saturated cohesionless soil with limited width behind the wall as the research object,and carries out the model test and finite element analysis.The main research work and conclusions are as follows:(1)By utilizing a self-made model box,this experiment is conducted to test active earth pressure of saturated cohesionless soil behind retaining wall under three displacement conditions,including rotation around bottom,translational motion and rotation around top.Besides,the damage form of the soil and the distribution rule of earth pressure are analyzed.The experimental results show that the fracture surface is cut off by the fixed retaining wall when the width of finite soil is narrow,and then the width of the fracture surface extends with the increase of the fill width,and finally the fracture surface stabilizes before it extends to the Coulomb fracture surface.The results of earth pressure test show that the distribution of limitedwidth soil pressure under the three displacement modes,which obviously smaller than that of the theoretical value obtained by method of calculating water and earth pressures separately.What's more,the distribution of soil pressure intensity increases with the increase of the fill width and finally approaches the theoretical value obtained by method of calculating water and earth pressures separately.When the retaining wall is rotating around the bottom,the earth pressure distribution is similar to the distribution of triangle shape.When the motion of retaining wall is translational,the earth pressure distribution becomes “spoon-shaped” distribution with the increase of the fill width.While it is rotating around the top,the earth pressure distribution is similar to the “S-shaped” distribution.(2)Through establishing a two-dimensional model of saturated-cohesive soil with limited width behind the wall,the development of the plastic zone behind the wall in three classical displacement modes of RB,T and RT and the influence of the filling width on the distribution of active earth pressure along the wall was simulated.The results obtained are similar to the results of model test.In addition,for RB mode,the influence of the external friction angle on the active earth pressure along the retaining wall was explored.Besides,the pressure of the exterior wall of basement was compared with the earth pressure on the active retaining wall.The results show that when the width of soil behind the wall is small,the friction angle between wall and soil has a significant effect on the distribution of active earth pressure,and the active earth pressure decreases with the increase of the soil pressure,the magnitude of the reduction is huge.With the increase of the width of the backfill wall,the influence of the external friction angle on the active earth pressure gradually decreases;The active earth pressure distribution curve of the active retaining wall and the lateral pressure distribution curve of the underground outdoor wall coincide within a certain height range of the retaining wall.However,in the area below the critical depth of conincidence,the lateral pressure of the underground outdoor wall is obviously greater than the active earth pressure of the movable retaining wall.