Study On Support Stability Of Overterm Serving Fine Sand Foundation Pit

In recent years,the development of western China is being carried out at a high speed.Many engineering problems caused by the special properties of fine sand have been encountered in the process of foundation pit excavation.Among them,"research on stability and treatment measures of unloaded slope of fine sand after long-term exposure" has gradually become a hot topic.A large number of studies have been carried out on the stability and treatment measures of fine sand slope at home and abroad,but there are few reports on the deformation mechanism,stability calculation method and treatment measures of fine sand slope under the condition of "long-term unloading".Therefore,it is of great significance to the calculation of the stability of the foundation pit support,the study of the supporting and strengthening measures of the foundation pit in the over-term service period and the study of the reuse of it.This paper studies the deformation mechanism of fine sand slope under the condition"over-term unloading",and base on this theory,through numerical simulation,study the condition of stress and deformation characteristics of the original fine sand slope supporting structure in over-term serving.The secondary supporting measures are put forward according to the results of the calculation,so that the over-term serving foundation pit supporting structure can satisfy the requirement of safety of foundation pit secondary use.The main work and achievements are as follows:(1)By referring to the relevant data,the current research on the long-term strength and deformation of fine sand foundation is summarized.Starting from the strength and deformation characteristics of fine sand foundation and the long-term stability of the supporting structure of fine sand foundation pit,the calculation theory and model required in this paper are established.(2)Study on slope stability of fine sand excavation section after long-term exposure.Mainly from the nature of silty sand and silty sand foundation pit deformation research,he stability of fine sand slope after a long time lateral unloading is studied through the predicted model,the over-term service silty sand strength parameters are got.By using the strength parameters for numerical simulation of the slope,the over-term serving fine sand slope lateral deformation considering time factor can be got,and further strengthening measures are proposed,the excavation slope stability meets the demand of foundation pit reuse,providing a reference of lateral deformation prediction of over-term serving fine sand foundation pit and secondary supporting.(3)An appropriate numerical simulation model was selected.By comparing the Mohr-Coulomb model with the Drucker-Prager model,the advantages and disadvantages of the two models were proposed,and the conversion mode of the two models was obtained,which provided theoretical preparation for the simulation of the over-term serving state of slope piles through soil creep effect.(4)Study on stability of over-term serving slope pile support structure considering creep effect of fine sand.Based on the long-term strength of fine sand obtained in the previous paper,the strength parameters were selected and a numerical analysis model was established to comprehensively evaluate the deformation of the over-term serving slope protection pile structure from the aspects of the change of lateral deformation along the depth,the surface settlement deformation after the slope protection pile structure and the relationship between the lateral deformation at different depths and time,etc.,through the comparison of different excavation depths and different pile diameters.On the basis of this study,the slope protection pile and the surface reinforcement measures behind the pile are put forward to reduce the deformation of the slope protection pile,so that the slope can meet the safety requirements of foundation pit reuse.(5)The foundation pit excavation is regarded as uniform unloading.Based on the numerical simulation results above,considering the creep effect of fine sand,from the aspects of bottom rebound of fine sand foundation pit with different distance of slope protection pile and the bottom of foundation pit with time,the spring-back capacity of the foundation pit with fine sand is evaluated comprehensively,so as to provide ideas for the determination of the unloading amount of fine sand foundation pit excavation from the perspective of numerical simulation.