Study On Soil Stability Of Xinzhengmen Site Based On Catastrophe Theory

China is one of the world's ancient civilizations.The historical process of the earthen sites extends from the Stone Age to modern times,It has historical positivism and non-renewability.It is an important material for us to study ancient culture.However,in the process of excavation and protection of earthen sites,there are many diseases such as denudation,cracks,instability and collapse due to the combined effect of external and internal stress.Therefore,it is imperative to correctly understand the mechanism that causes the predisposing factors of soil disease to be extremely degraded,strengthen the concept of soil site protection.At present,domestic and foreign scholars have carried out systematic research on the soil properties such as expansive soil,collapsible loess and saline soil for drying-wetting,freezing-thawing cycles and salinization processes,and achieved relatively satisfactory results.Relatively speaking,there are fewer studies on earthen sites,especially on the changes of micro-structure of macro-appearance of soil deterioration.Therefore,it is of great value and significance to understand the mechanism and essence of macroscopic phenomena of soil instability from the micro-perspective.In this paper,based on the analysis of the site investigation,historical status,environmental characteristics,stratum lithology and hydrogeological conditions of Xinzhengmen site,a new method of soil stability analysis based on the mechanical model of plane sliding instability of elastic slip mass is established,focusing on the soil stability of Xinzhengmen site.The contents of the research embraces three principal sections:(1)Determine the analytical method.Based on the demonstration,non-renewability and accuracy of computer simulation function of earthen sites,numerical simulation is selected to analyze their mechanical properties;Because there are cracks and weak interface between old and new soil in Xinzhengmen earth site,the plane sliding instability mechanics model established by Professor Qin Siqing is most suitable to analyze its stability;Based on Huang Wenxi s classification of the meso-structure of unsaturated soil and the low water content of the site,the water-sealing form was selected to analyze the mechanical properties of the site soil;Based on literature review and comparative analysis of suction theory of unsaturated soils,the effective stress of unsaturated soils is analyzed from the perspective of intergranular suction.(2)The non-linear medium constitutive relation of Xinzhengmen earthen site is given.Based on the suggestions of Professor Chen Zhenghan and Academician Shen Zhujiang on the micro-structure of soil,a simplified model of ideal equal-size soil particles is established,which regards the soil site as composed of particles at the micro-level.Based on the analysis of physical and mechanical parameters of Xinzhengmen site soil,the stress-strain relationship of soil with different moisture content under self-weight and loading conditions was simulated and analyzed by finite element software.Using MATLAB to fit the simulation results,the constitutive relation of the non-linear medium of Xinzhengmen earthen site is given as follows ?=Gf(?)e-(u/u0)2(3)Cusp catastrophe analysis based on elastic slip mass.Considering the influence of deformation and energy accumulation of slipping mass on soil stability in the process of soil development,a mechanical model of elastic slipping mass is established.Based on the general formula of the constitutive relation of the soil in Xinzhengmen site obtained by finite element simulation and the mechanical model of plane sliding instability,the cusp catastrophe model for different assumptions of sliding body is analyzed.The mechanical model of rigid slipping mass only explains the instability of the slipping mass,but ignores the influence of the sliding body on the stability of the soil.The calculation results of the model show that the instability will occur when the moisture content of the medium on the weak surface is more than 38%.The calculation results of the elastic slipping mass mechanics model also explain the failure and instability of the slipping mass caused by dilatation,bulge or bending.At the same time,it is concluded that when the moisture content of the soft surface medium is more than 29%,the instability will occur.Through comparative analysis,the mechanical model of elastic sliding body is more in line with engineering practice and considers more comprehensively,and the stability coefficient obtained is more convincing.It also provides a new idea for other methods of soil stability analysis with weak surface.