Experimental And Constitutive Theory Study On Unloading Deformation Of Clay Considering The Influence Of Initial Principal Stress Direction

Foundation pit engineering has significant excavation unloading characteristics.A clear understanding of the stress and deformation characteristics of soil under excavation unloading conditions is beneficial for better simulation analysis and design calculation of foundation pit engineering,which can optimize design and ensure the safety and stability of the excavation construction process.At the same time,in practical engineering,not only does the magnitude of principal stress change in the foundation soil unit,but the direction of principal stress also deviates,resulting in differences in the mechanical characteristics of the soil in different principal stress directions.Therefore,the indoor test method was adopted in this article,taking Jinan remolded clay as the research object to conduct triaxial unloading tests and constitutive theory research considering the influence of different initial principal stress directions.The research content and main research results are as follows:(1)The mud pressure consolidation method has been used to develop a device for preparing large diameter reshaped clay samples.By testing the moisture content and density of the samples,it is determined whether the uniformity and repeatability of the prepared samples can meet the requirements of subsequent triaxial tests.The test results prove that the uniformity and repeatability of the samples are good.(2)By sampling in different directions with different angles to the deposition direction,the changes in the initial principal stress direction angles of the samples are achieved.The sampling directions are 0 °,30 °,45 °,60 °,and 90 °,respectively.The samples are used for triaxial compression tests and lateral unloading tests to explore the stress-strain relationship,strength,initial tangent modulus,and other mechanical properties of clay under different initial principal stress directions.(3)Evaluate the advantages and disadvantages of different constitutive models and their specific applicability,summarize different improvement methods for several types of constitutive models,and select appropriate constitutive models for correction based on lateral unloading stress paths.Among them,the focus is on studying the basic theory of the Duncan Zhang model and the algorithm for solving various parameters.Based on the theoretical foundation of the Duncan Zhang model,considering the influence of unloading stress path,an empirical expression for the tangent deformation modulus of the Duncan Zhang model that can reflect the lateral unloading effect is established.(4)After processing and analyzing the results of the triaxial test,the parameter determination values of the Duncan Zhang correction model considering the changes in the initial principal stress direction angle were obtained.The variation patterns of each parameter with the initial principal stress direction angle were plotted.Origin software was used to fit the data and obtain the functional relationship between some parameters of the Duncan Zhang correction model and the changes in the initial principal stress direction angle under the lateral unloading stress path.