Research On The Deformation Characteristics Of Loess Pit Excavation Based On Hardening Soil Small

With the acceleration of urbanization in China,the development of underground space in loess areas is gradually increasing,and the requirements for loess foundation pit engineering are getting higher and higher.The deformation analysis of loess foundation pit usually selects the traditional principal structure model for numerical simulation analysis,however,the selection of principal structure model and the value of parameters in numerical simulation determine the quality of foundation pit deformation analysis.Meanwhile,for the design of complex pits,designers usually make the design according to the pit deformation under plane strain conditions,which is quite different from the real three-dimensional size pits,and it is very necessary to study the spatial effect of complex pits.In this paper,for the complex foundation pit project in the loess area of Tongchuan,the relevant research on the intrinsic model and intrinsic model parameters of the foundation pit loess is done through theoretical analysis,indoor test,numerical inversion and numerical simulation,and on this basis,the deformation law of the excavation of the loess foundation pit considering the spatial effect is obtained,and the main research contents are as follows:(1)A theoretical analysis of the common intrinsic constitutive model of pit loess was conducted,and the selection basis of the intrinsic constitutive model of pit loess was summarized by combining the stress path characteristics,small strain characteristics and other mechanical characteristics of the pit loess.(2)The characteristics of HSS model parameters are analyzed,and a comprehensive selection scheme of HSS model parameters is proposed:strength parameters c、φ、Rf,and stiffness-related parameters Eoedref、E50ref、Eurref、m,are suitable to be obtained by indoor test methods,small strain parameters Goref and γ0.7,are suitable to be obtained by numerical inversion methods,and other minor parameters can be obtained by empirical methods.(3)The mechanical and deformation characteristics of in-situ loess were analyzed by several sets of in-situ loess standard consolidation tests,triaxial consolidation and drainage shear tests and triaxial consolidation and drainage loading and unloading tests,and some strength and stiffness parameters of the HSS model of Tongchuan loess were obtained;the GABP neural network model was repeatedly trained by 49 sets of numerical tests,and the nonlinear mapping rule of the pit displacement and small strain parameters was established,and the input The small strain parameters were obtained by inversion of monitoring data;the secondary parameters of HSS model were obtained by empirical method;the proportional relationship between the stiffness parameters and compression modulus of HSS model was obtained by the above research;the research results of HSS model parameters of different soil layers in different regions were statistically analyzed,and the recommendations of HSS parameters in the loess region of Tongchuan were given.(4)Based on the above research,a three-dimensional numerical model of a loess pit in Tongchuan was established,and the differences between HSS model,HS model and M-C model in the calculation of deformation of specific pit projects were compared and analyzed,and explanations were given;the superiority of HSS model in the analysis of loess pit deformation and the rationality of the HSS parameter taking method in this study were verified by combining the field monitoring data.(5)Through the three-dimensional numerical model,the deformation characteristics of the excavation and support process of loess foundation pit are analyzed,and the deformation laws of foundation pit enclosure structure,surrounding surface settlement and pit bottom uplift under the influence of shaded corner,positive corner and asymmetric excavation are obtained.