Study On Deformation Characteristics Of Abnormal Deep Foundation Pits Excavation In Coastal Granite Residual Soil Layer

The coastal areas of Fujian are mostly in the granite residual soil layer,and with the rapid development of rail transit in coastal areas,more and more abnormal deep foundation pit were appeared,which have complex structure stress and obvious three-dimensional effect.So study on deformation characteristics of abnormal pits excavation in coastal granite residual soil layer would have great engineering significance and theoretical value.On the basis of the abnormal deep foundation pit in Xiamen subway LvCuo station,the paper studied the deformation characteristics caused by excavation of foundation pit under groundwater by similar model test to abnormal pits excavation in coastal.The similiarity model test of abnormal deep foundation pit in coastal,and the dynamic mechanical effect of foundation pit excavation under ground water,based on similar theories and the result of soil test,analyzed the spatial effect of foundation pit excavation which have negative corner by FLAC30 software,finally based on the elastic half space Melan's solution,the elastic displacement calculation methods of analytic solution is further established to give the influence of excavation and unloading.The main conclusions of this paper are as follows:(1)Results of laboratory soil test of coastal granite residual soil layer about LvCuo station,Xiamen subway showed that the soil particle size was relatively continuous,they were not expansive soil,with weak permeability,The bear disintegration index was low,while the disintegration is strong.The vertical compressive modulus of soil increased with the increase of axial pressure,the strain type of soil was in accord with the typical strain hardening model.(2)The result caused by excavation of deep pit showed that the excavation of abnormal had obvious steric effect on shaped corner,this effect was more obvious when the depth of excavation was deeper.the deformation increased about 15%when the effect of groundwater was considered into the model.(3)Using FLAC3D to analys the spatial effect of foundation pit excavation which had negative corner showed that with the negative angle increasing,the lateral displacement of the angle increased by exponential approximately.The position of the maximum ground settlement was contiune to closer to the angle position,the maximum value first increased and then decreased,and reached the maximum at 60 degrees.The lateral displacement of the angle increased first,then slowly decreasd with the length of negative angle increasing.The maximum settlement value and position constantly increased.Finally,the result of numerical simulation based on the LvCuo station showed that the length of enclosure structure was greater than the size of the angle about the influence coefficient on the space effect.(4)The calculation model of foundation pit deformation was established based on the Melan's solution,and the stress solution of elastic half space under the action of horizontal non-uniform distribution of linear load was obtained.By determining the state of each point of the foundation pit soil and using the constitutive relation considered the influence of loading and unloading elastic modulus in the plane strain problem to calculate the modulus value of the corresponding point.The deformation of foundation pit was modified by the modulus,and on this basis,the earth pressure was calculated,by the lateral displacement,which made the calculation method of foundation pit deformation more reasonable.Finally,the feasibility of the method was verified by an engineering example.