Model Test Study On Interaction Between Soil And Retaining Structure Under Excavation Bias

With the accelerated development of urban construction,many foundation pit projects have emerged in close proximity to buildings.This foundation pit is subjected to asymmetrical loads on both sides to form a biased foundation pit.At present,most scholars are focused on the study of the deformation of the foundation pit under symmetrical load and the deformation mechanism of the soil around the foundation pit.The deformation of the foundation pit under stress and the deformation of the surrounding soil will change greatly,and it will show asymmetric deformation.At present,there are no relevant standards and specifications to make special provisions on its design,construction and other issues.Therefore,a correct understanding of the interaction mechanism of the foundation pit enclosing structure and the soil under the effect of bias pressure and the deformation of the foundation pit under bias pressure have certain certainness for engineering guidance significance.In this paper,based on the similarity theorem,the similarity relationship of the model test of the foundation pit is deduced.The model test of the cantilevered foundation pit under bias and the model test of the internally supported foundation pit under bias are carried out,respectively.The deformation characteristics of the foundation pit under pressure,and the relationship between the interaction between the envelope structure of the two types of foundation pits and the soil under the bias pressure are given.The main work results are:(1)Through the second similarity theorem,the similarity of the model test is deduced,the envelope structure,internal support and soil sample model materials are determined.The design model box size is 2.5m × 2.0m × 1.5m.(2)Through the model test of the cantilever foundation pit under bias,the characteristics of the deformation of the cantilever foundation pit under stress and the deformation of the soil are studied.It was found that during the bias loading process,the lateral earth pressure on the outside of the biased side envelope showed a decrease in the upper part and an increase in the lower part;the lateral earth pressure on the outside of the non-biased side envelope showed a decrease in the upper part,The lower part increases slightly.Under the action of bias,the horizontal displacement of the bias side enclosure is greater than that of the non-biased side enclosure.The maximum displacement of the top of the bias side enclosure is 3.21 mm,which is 1.07% of the maximum depth of the foundation pit.The maximum displacement of the point closest to the envelope on the biased side is 0.17mm;the maximum displacement of the surface settlement on the unbiased side is 0.53 mm.(3)Through the model test of the internally braced foundation pit under bias,the characteristics of the mechanical deformation and soil deformation of the supported foundation pit under the bias are studied.During the excavation,the upper part of the non-biased side enclosure structure moves to the outside of the foundation pit,the lateral earth pressure on the upper part increases,and the middle and lower parts of the unbiased side enclosure structure move to the inside of the foundation pit,and the middle and lower lateral earth pressure Decrease.During the bias loading process,the foundation pit enclosure moves to the non-biased side as a whole,and the lateral earth pressure on the outside of the enclosure on the bias side shows that the upper part decreases and the middle and lower parts increase;the non-biased side enclosure The lateral earth pressure on the outside of the protective structure shows an increase.The maximum displacement of the biased side envelope is 2.01 mm,which is 0.67% of the maximum depth of the foundation pit.The maximum displacement of the upper part of the unbiased side enclosure to the outside of the foundation pit is 0.32 mm,which is 0.11% of the maximum depth of the foundation pit.The lower part of the non-biased side enclosure structure moves toward the inside of the foundation pit,and the maximum displacement is 0.16 mm during the completion of the excavation,which is 0.05% of the maximum depth of the foundation pit.Under the effect of bias pressure,the uplift displacement of the soil body near the unbiased side enclosure structure is 0.082 mm.The maximum surface settlement displacement is 0.14 mm.The ground surface shows uplift displacement closer to the envelope,and the maximum uplift displacement is 0.05 mm.(4)Through the analysis of the results of the cantilevered foundation pit model test under bias and the internally supported foundation pit model test under bias,the interaction relationship between the two foundation pit retaining structures and the soil under the bias pressure is given and In the overall deformation mode of the foundation pit,it is found that there is a certain difference in the action relationship between the soil and the envelope structure of the two foundation pit modes under the bias pressure.(5)The cumulative amount of deformation displacement of the cantilevered foundation pit and the cumulative displacement amount of the internally supported foundation pit under the bias pressure are converted by the similarity ratio,and compared with the standard control value.It was found that under the effect of bias,the top displacement of the cantilevered foundation pit bias side envelope and the settlement displacement of the ground surface have exceeded the standard control value,where the foundation pit is easy to reach instability;the bias of the internal support foundation pit The horizontal displacement at the deep layer of the side foundation pit envelope structure exceeds the normative control value.In actual engineering,attention should be paid to the effect of bias in the foundation pit.