Analysis On Performance Of Excavation Cantilever Pile Support Struction Under Finite Earth Pressure

In the practicall deep foundation pit engineering design,there is often a situation where the distance between the supporting structure of the foundation pit to be excavated and the existing building underground structure is relatively small.At this time,the soil width between the supporting structure and the adjacent underground structure is small.,resulting in limited earth pressure.However,the classical earth pressure theory is based on the assumptions of semi-infinite soils,which is clearly not applicable for soils of limited width.In this paper,the theoretical analysis and numerical simulation of the earth pressure of finite width soil in the above situation are carried out.The main contents and research results are as follows:1.Based on the limit equilibrium theory,regardless of the reaction force of the basement side wall and the influence of the friction force,the finite soil of the external wall of the building near the foundation pit is less than the distance between the foundation pit structure and the height of the basement structure.Stress proposes a simplified calculation method.The comparison proves that the method can be used to simplify the calculation of the finite earth pressure.2.Based on the actual engineering data,the Mohr-Coulomb constitutive model and the modified Mohr-Coulomb constitutive model are used respectively to compare and analyze the difference between the calculation results of the two models.Compared with the Mohr-Coulomb model,the modified Mohr-Coulomb constitutive model can simulate a double hardening process that is unaffected by shear failure or compression damage.Combined with the actual engineering monitoring data,it is proposed that the reasonable value range of the correction factor n of the modified Mohr-Coulomb model is in the range of 0.8-1.0.3.Using numerical simulation method,analyze the earth pressure distribution of finite soil pressure and the classical earth pressure theory during foundation pit excavation.It is concluded that compared with the distribution characteristics of classical earth pressure,the finite soil pressure will be significantly reduced within a certain depth range,and the reduction size is affected by many factors.The influence of the internal friction angle of the soil on the soil pressure of the finite soil is greater than the cohesion of the soil.The width of the finite soil is the main factor affecting the finite soil pressure,and the ratio of the width of the soil to the depth of the foundation pit.When the ratio is greater than or equal to 1.4,the earth pressure on the foundation pit supporting structure is basically the same as the infinite earth pressure.4.By establishing a finite element model,the variation of the force between the pile-supporting + soil-nail composite retaining structure and the row pile without soil nails under the action of finite soil pressure in homogeneous soil layer is analyzed.When the ratio of the width of the finite soil to the excavation depth of the foundation pit changes from 1.4 to 0.2,the overall stability coefficient of the pile-supported + soilnail composite support structure is increased by about 43.4%,and the maximum horizontal displacement of the pile top is reduced by 71.7%.The maximum bending moment of the pile was reduced by approximately 51.9%.It can be concluded that when the width of the limited soil is small,the piles with the soil nails can significantly reduce the horizontal displacement of the pile top,reduce the force on the piles and improve the overall stability of the foundation pit.