HCMW Engineering Method For Foundation Pit Support Design Method And Its Application Research

Precast I-shaped reinforced concrete pile embedded in cement-soil mixing pile is a new supporting engineering method(HCMW engineering method),which has been occupied by the supporting system,because the advantages of reducing the space,saving material,environmental protection and free recovery,etc.In order to promote the application of this method,the design method,supporting mechanism and supporting effect should be further studied.In this paper,the design method and support application effect of HCMW engineering method are studied through the indoor model test and the support project of Changzhou.The main contents and conclusions are as follows:(1)Based on the summarization of relevant data,two equivalent design methods of I-shaped piles and the method of determining the diameter and depth of cement-soil piles are studied in this paper.At the same time,the bearing capacity and stability checking calculation of the support system are comprehensively expounded,which provides reference for the design of HCMW engineering method.(2)The test results are discussed in terms of the distributing of earth pressure,the variety with excavation situation,comparing with Rankine limit earth pressure.Based on this conclusion,the approximate trapezoidal distribution of soil pressure on pile back in the support system is obtained.At the same time,the measured active earth pressure is slightly larger than Rankine active earth pressure due to the influence of rotation effect in the displacement of support structure.(3)By monitoring and analyzing the horizontal displacement of pile top in the model test,it is found that the deformation process of the supporting structure can be divided into four stages:initial,stability,displacement growth and failure.By studying the embedding depth and the horizontal displacement of pile top,the critical embedding ratio of the model system is obtained λ=0.46.Based on the principle of minimum potential energy and considering the contribution of soil-cement stiffness,the analytical solution of maximum horizontal displacement of pile top is obtained.At the same time,the research also shows that the deformation of the supporting structure is affected by the cement soil,which provides 39.001%of the rigidity of the supporting structure.(4)Combined with flac3d software,the pile displacement,pile top settlement,ground settlement and soil deformation in the actual project are analyzed.The results show that the design meets the deformation control requirements of the second-level foundation pit.At the same time,Flac3d simulation analyzed the influence of support structure under different soil-cement stiffness,and the results shows that the maximum displacement of pile body and the elastic modulus of soil-cement presented a nonlinear change rule.The stress of pile body first decreases and then increases.It is considered that the elastic modulus of soil-cement should be controlled about 400-600 MPa.