Research on deep clay high pressure triaxial unloading and structural constitutive model

摘要

The difference of engineering geological behavior between deep and shallow soil is analyzed by taking the clay buried at a depth of -300—600 m as the research object. In consideration of the natural stress level of deeply buried soil and variation in its unloading stress during the coal mine shaft excavation, triaxial high pressure unloading tests for unloading of confining pressure and axial pressure holding are conducted at triaxial equipressure of 11 MPa, 12 MPa and 14 MPa, respectively, triaxial high pressure unloading deformation and strength characteristics of deep clay are analyzed, CT device is utilized to investigate structural change inside the test specimens during the triaxial high pressure unloading tests, and the essential characteristics of structural change due to deformation and damage of deep clay under high pressure unloading condition are revealed. On this basis, a structural change parameter mq which is based on deep soil deformation and can reflect change of soil structure with the change of volumetric and deviatoric strain is proposed, and by applying this structural change parameter mq in the stress-strain relationship, a structural constitutive model that can reflect the essential change of high pressure unloading mechanics of deep clay is built.