Analysis And Research On Soil Retaining Effect Of Cement-soil Waterproof Curtain In Deep Foundation Pit Support

When the underground water level in the large area of foundation pit is higher than the basement,the combined support of waterproof curtain and row piles is often used.Waterproof curtain generally adopts mixing pile or high pressure jet grouting pile,to prevent the external groundwater into the foundation pit,using pile structure to bear the water and soil pressure outside the foundation pit.However,in practical engineering,the water-stop curtain can not only prevent groundwater from entering the foundation pit,but also bear part of the water and soil pressure,and also reinforce the soil outside the foundation pit.At present,the retaining effect of waterproof curtain will not be considered in the design process.In the design process of supporting structure,conservative design is generally carried out,leaving a large safety reserve.Ignoring the retaining effect of waterproof curtain will make the design more conservative and cause waste of resources.This paper mainly does the following research.(1)Using PLAXIS 3D software,the numerical simulation calculation is carried out when the high pressure jet grouting pile waterproof curtain is used as the foundation pit supporting structure alone.The effect of water-stop curtain retaining is studied.The retaining effect is related to the setting depth,row number and elastic modulus of waterstop curtain.With the increase of row number and elastic modulus of water-stop curtain,the deformation of foundation pit will be inhibited to a certain extent.(2)The numerical simulation software is used to analyze the retaining effect of waterproof curtain in the composite structure of waterproof curtain and row piles.Considering the retaining effect of waterproof curtain,the maximum horizontal displacement of retaining structure can be reduced by 40.12 %,the bending moment can be reduced by 41.27 %,the shear force can be reduced by 29.15 %,and the settlement of soil outside the foundation pit can be reduced by 52 %.(3)In the composite structure of waterproof curtain and row piles,the row number,depth,distance from row piles and elastic modulus of waterproof curtain will affect the horizontal displacement,bending moment of retaining structure and the settlement of soil outside the foundation pit.When considering the retaining effect of the waterproof curtain,the number of rows of the waterproof curtain should be considered first,followed by the setting distance and elastic modulus.The study found that the depth of the waterproof curtain has little effect on the retaining effect,and it can meet the minimum impermeability requirement depth when setting.With the increase of the row number and elastic modulus of the waterproof curtain,the horizontal displacement,bending moment of the retaining structure and the settlement of the soil outside the foundation pit can be inhibited.By studying the distance between the waterproof curtain and the retaining structure,it is found that when the lapping is not considered,the maximum horizontal displacement,bending moment and soil settlement outside the foundation pit of the retaining structure decrease first and then increase with the increase of the distance.(4)Based on a foundation pit project in Suzhou City,the influence of the retaining effect of the waterproof curtain on the foundation pit is numerically simulated.It is found that the monitoring values of the deep horizontal displacement of the foundation pit and the settlement of the soil outside the foundation pit are roughly the same as the deformation trend of the numerical simulation results and the maximum error is within10 %.It is suggested that the retaining effect of the waterproof curtain should be considered in the design.Figure [90] Table [9] Reference [79]...