Study On Deformation Behavior Of Foundation Pit In Soil-rock Mixed Strata

With the development and utilization of underground space, the safety andeconomy of the foundation pit has become a hot research focus. But the study on thedeformation behavior of foundation pit in soil-rock mixed strata is not verycomprehensive. The deformation behavior of foundation pit in soil-rock mixed stratahas been analysised in the paper, so as to provide references for engineeringapplication, it has important practical significance.Numerical simulation of deep excavation has been done, deformation ofretaining structures and ground settlement after the excavation in different conditionshas been analysised in the paper, some conclusions can been drawn.For excavation of pile-inner bracing structures:(1) In order to inhibit the deformation at the bottom of pile, the pile need topenetrate the strong weathered strata, embed the moderately weathered strata at least0.5m when the excavation face is under the rock-soil interface.The deformation curveof the pile is convex, the maximum of the pile deformation often locates at the middleof the pile.(2) The main cause of the final ground settlement is the excavation of soil. Forthe excavation including strong weathered strata, it’s1.5~3.0times of soil thickness.For the excavation including moderately and slightly weathered strata, it’s0.7~1.3times of soil thickness.(3) The ratio of maximum ground settlement to maximum pile deformation is0.5~0.7, The distance between the position of the maximum ground settlement and thesideline of the foundation pit is0.5times of soil thickness.(4) When there is temporary surcharge on the side of foundation pit. It hassignificant effect on ground settlement in the range which extends from the centerposition for1.0~2.0times of surcharge width. When the surcharge width is less thanor equal to1.0h, h refers to excavation width, the maximum ground settlement locatesat the middle of the surcharge. When the surcharge width is bigger than1.0h, itlocates at the middle of the surcharge whose width is1.0h. The ratio of maximumground settlement to maximum pile deformation is2.0~5.0. For excavation of pile-anchor retaining:(1) The model of ground settlement is skew distribution and the deformationcurve is smooth when the deformation curve of pile is triangle which is big top andsmall bottom. The model of ground settlement is irregular skew distribution, thedeformation curve is less smooth and has two extreme value when the deformationcurve of pile is trapezoid which is big top and small bottom. The maximum of the piledeformation often locates at the top of the pile.(2) In order to reduce the influence of excavation of rock on the groundsettlement, the pile need to penetrate the strong weathered strata when the soil is thick,the insertion ratio of the pile embeds into the strong weathered strata should be morethan0.5; the insertion ratio should be more than0.2when there are only moderatelyand slightly weathered strata in the excavation. The excavation of rock will not haveobvious influence on the ground settlement if the supporting structure of foundationpit satisfies the conditions above.(3) For the excavation including strong weathered strata, the range of the groundsettlement is4.0times of soil thickness. For the excavation including moderately andslightly weathered strata, it is2.5times of soil thickness.(4) The ratio of the maximum ground settlement to the maximum piledeformation is0.4~0.5when the excavation of rock has obvious influence on theground settlement, vice versa, the ratio is0.5~0.7. The distance between the positionof the maximum ground settlement and the sideline of the foundation pit is0.2~0.3times of soil thickness.(5) When there is temporary surcharge on the side of foundation pit: Thedeformation curve of the pile is triangle or trapezoid that is big top and small bottom,which is similar to the situation without surcharge. It has significant effect on groundsettlement in the range which extends from the center position for0.7~1.0time ofsurcharge width. When the surcharge width is less than or equal to1.0h, the maximumground settlement locates at the middle of the surcharge. When the surcharge width isbigger than1.0h, it locates at the middle of the surcharge whose width is1.0h. Theratio of maximum ground settlement to maximum pile deformation is1.0~2.5.