Experimental Study On The Lateral Earth Pressure Of Foundation Pit Adjacent To Composite Foundation With Rigid-flexible And Long-short Piles

With the development of the city,land resources become scarce,and the building density in the central urban area is increasing.When the foundation pit is newly excavated in the central urban area,the influence of existing buildings on the earth pressure of the supporting structure of the adjacent foundation pit should be considered.Composite foundation with rigid-flexible and long-short piles has been widely used in many areas of our country because of its excellent spatial bearing capacity and good economic benefits.However,at present,the relevant research on the earth pressure of the foundation pit adjacent to composite foundation with rigid-flexible and long-short piles is not comprehensive,and the current code does not make detailed provisions on this problem.Based on the above reasons,firstly,through the model test,this paper makes a systematic study on the distribution and evolution law of the earth pressure of the pit adjacent to composite foundation with rigid-flexible and long-short piles.Then the influence of different design parameters of composite foundation on the earth pressure of adjacent retaining wall is analyzed by FEM.Finally,based on the results of model test and FEM analysis,the shortcomings of the existing code for calculating the earth pressure of the foundation pit adjacent to existing buildings are summarized,and the calculation method of the earth pressure of the foundation pit adjacent to composite foundation with long-short piles is proposed.The main conclusions of this paper are as follows:(1)when the retaining wall does not move,the additional lateral earth pressure acting on the retaining structure adjacent to composite foundation with rigid-flexible and long-short piles reaches a maximum at the depth near the end of the short pile.When the displacement of the retaining wall occurs,the phenomenon that the additional lateral earth pressure of the retaining structure reaches a maximum at the depth near the end of the short pile still exists.Therefore,the influence of surcharge load transmitted by short piles should be considered when calculating the lateral earth pressure acting on the retaining structure adjacent to composite foundation with long-short piles.(2)When the upper load remains unchanged and the retaining wall displaces,the additional lateral earth pressure acting on the retaining structure adjacent to composite foundation with long-short pile is less than that of the natural foundation in the depth of upper area of the retaining structure.The existence of rigid-flexible long-short-pile composite foundation reduces the diffusion of additional load in the soil to the side wall of the adjacent foundation pit.(3)The parametric analysis is carried out by FEM.With the increase of the length of the short pile,the position of the maximum lateral earth pressure of the retaining structure near the end of the short pile decreases,and with the increase of the modulus of the short pile,the value of the maximum lateral earth pressure of the retaining structure near the end of the short pile does increases.(4)It was found that the lateral earth pressure of the foundation pit adjacent to composite foundation with long and short piles can approximately be estimated as equivalent to the algebraic sum of the surcharge load borne by soil between the piles and the remaining surcharge load borne by short and long piles.Based on this,a revised formula for calculating the lateral earth pressure acting on a retaining structure adjacent to composite foundation with long and short piles is proposed.