Experimental Investigation On Earth Pressure Of Foundation Pit Adjacent To Existing Soil-cement Pile Composite Foundation

In the nineties of the last century,the soil-cement pile composite foundation has been widely used in the process of urbanization from mid-rise buildings to high-rise buildings.In recent years,with the upgrading of the old urban areas and the demolition of city villages,the construction speed and scale of high-rise buildings are increasing,and the building density is also increasing,which leads to more and more foundation pit projects,especially those adjacent to the existing soil-cement pile composite foundation.The calculation method of foundation pit earth pressure in China's current national and local codes has not been completely and accurately regulated.In this paper,indoor model test and numerical simulation are used to study this problem.In this paper,three displacement modes(stationary,rotating and translational)are simulated by setting up rigid retaining walls,and indoor model tests are established to obtain the distribution characteristics of static and active earth pressure on the side wall of foundation pit under the condition of adjacent natural foundation and soil-cement pile composite foundation.Based on the comparative analysis of the tests,the distribution characteristics and variation law of the earth pressure of the retaining wall under the condition of adjacent soil-cement pile composite foundation are obtained.In addition,the finite element simulation software is used to establish the numerical analysis model of the same size and loading regime,which is compared with the model test results.The influence of pile body modulus,pile spacing and the spacing between composite foundation and retaining wall on the earth pressure of retaining wall is discussed by variable parameter analysis.Through the above research,the main research results are as follows:(1)When the distance between the supporting retaining wall and the soil-cement pile composite foundation is 0.1H(H is the height of the retaining wall),and the length of the soil-cement pile is 0.6H,the additional earth pressure on the retaining wall presents a "hump shape" along the depth,and the main influence range of the upper additional load is 0.1H ? 0.4H and 0.6H ? 0.9H.Under the condition that the retaining wall rotates outward(translational)displacement,the additional earth pressure above 0.6h of the retaining wall gradually decreases and tends to a stable value with the increase of the rotational(translational)momentum,and the additional earth pressure below 0.6h of the retaining wall gradually increases and tends to a stable value with the increase of the rotational(translational)momentum.(2)When the bottom of pile is above the bottom of the foundation pit and the soil stress between the composite foundation piles is equal to the surface stress of the natural foundation,the additional retaining wall earth pressure produced by the composite foundation is less than the additional earth pressure produced by the natural foundation due to the blocking effect of the soil-cement piles on the soil mass within the range of the consolidation treatment depth of the soil-cement piles.However,under the treatment depth of the soil-cement pile,due to the influence of pile end resistance,the additional retaining wall earth pressure of composite foundation is greater than that of natural foundation.(3)When the bottom of pile is higher than the bottom of the foundation pit and the code(DBJ 41 / 139-2014)is used to calculate the static earth pressure adjacent to the soil-cement pile composite foundation,the calculation results above the bottom of pile are more safety;however,the calculation results below the pile end are unsafe.It is suggested that the influence of pile end resistance on the deep earth pressure of foundation pit should be considered when calculating the earth pressure of foundation pit adjacent to the soil-cement pile composite foundation.(4)By ABAQUS finite element software,the influence of elastic modulus of pile material,pile spacing and distance between composite foundation and retaining wall on earth pressure of retaining wall is studied.The results show that the larger the elastic modulus of pile material,the smaller the earth pressure of retaining wall in the range of consolidation depth of soil-cement pile composite foundation,and the larger the earth pressure of retaining wall below the consolidation depth of soil-cement pile composite foundation;the larger the pile spacing,the greater the earth pressure of each point of retaining wall;the larger the distance between composite foundation and retaining wall,the smaller the influence of additional load of composite foundation on the earth pressure of each point of retaining wall.