Experimental Study On Mechanical Properties And Fractional Damage Constitutive Model Of Unsaturated Chengdu Clay

As China’s major policies gradually incline to the western region,especially the southwest region in response to the country’s commitment to building a double-city economic circle in Chengdu-Chongqing region,the construction and investment in infrastructure are increasing day by day.Classical soil mechanics mainly takes saturated soil as the main research object.However,in the natural state,the soil is basically in the unsaturated state,and its properties are often deviated from the interpretation of the basic principles and concepts of classical soil mechanics.The existence of gas phase in soil makes it difficult for people to fully grasp the properties of unsaturated soil.As a result,all kinds of accidents caused by insufficient understanding of unsaturated soil in Chengdu-Chongqing area are gradually increasing,resulting in a large amount of loss and waste of manpower,material resources and financial resources.Therefore,this paper intends to carry out basic physical and mechanical tests on unsaturated Chengdu clay of a foundation pit project in Dayun Village,Longquanyi District,Sichuan Province,and study the stress-strain characteristics of the soil under loading conditions.The main research contents are as follows:(1)The basic physical property test and soil-water property test were carried out on the unsaturated Chengdu clay from the Dayun Village through the indoor geotechnical test.The basic physical property index of the unsaturated Chengdu clay and the soil-water property rule of the soil were defined.The function relationship between matron suction and water content was established to further clarify the soil and water properties of the unsaturated Chengdu clay.It provides a necessary basis for the subsequent mechanical properties test and constitutive model construction of unsaturated Chengdu clay.(2)Through direct shear test and triaxial test,the stress-strain characteristics,initial elastic modulus and damage strength characteristics of unsaturated Chengdu clay in Dayuncun are analyzed.The test results show that the stress-strain curves are obviously strain hardening type,and the shear strength index rule of unsaturated Chengdu clay in this area is also defined.Fredlund strength theory was used to analyze the test results,and the rule of index parameterφ_bwas obtained.(3)Because of the distribution of soil moisture content and the effect of load,the soil humidity field and stress field,which was formed in double field determines the mutual coupling effects of the physical and mechanical properties of unsaturated clay in chengdu,so in the model with double damage variable to simulate the humidity field and stress field coupling,the introduction of fractional order calculus theory describe the strain hardening properties of unsaturated clay,A constitutive model which can accurately reflect the unsaturated soil properties and strain hardening laws of soil in the moisture and stress fields is established.(4)Through the characteristic analysis of the relevant parameters of the model,and combining with the experimental data obtained from the triaxial test and the relevant literature,the fitting verification shows that the constitutive model is scientific and reasonable.The research results of this paper deepen the understanding of soil-water characteristic curve of unsaturated Chengdu clay,clarify the strength characteristics and strain hardening properties of unsaturated Chengdu clay,and provide reference for the design of foundation pit,slope and other engineering and the theoretical research of unsaturated Chengdu clay in the future.