Experimental Study On Mechanical Properties Of Rock Unloading Creep Under High Stress And Pore Pressure

With the rapid development of China's construction industry today,the engineering problems under the action of high buried stress can not be ignored more and more.Deep underground tunnel,deep underground mining and excavation as well as high slope excavation are all affected by high ground stress.The unloading stability of rock mass in such projects has become the core problem that needs to be solved urgently in the field of high ground stress engineering construction in China.So,This chance is a important significance to study the creep mechanical properties of sandstone under high stress and high water pressure.Supported by the key project of The National Natural Science Foundation of China(51439003),"Deformation and failure Mechanism and Protection of reservoir bank Slope under Complex Conditions",this paper studies the mechanical properties of sandstone in the Three Gorges Reservoir area through laboratory mechanical tests and draws relevant conclusions.The main research contents are as follows:1)Conventional uniaxial tests,triaxial instantaneous mechanical tests under high stress and high stress and high water pressure coupling were carried out on sandstone,analysis of the deformation characteristics of the sample,intensity brittle delay transformation rule and failure mode of high stress and high water pressure and deformation of sandstone are discussed characteristic parameters(elastic modulus,peak strain,etc.),strength characteristics(cohesive force,internal friction Angle,etc.).It provides the basis for further rock unloading creep test and theoretical research.2)Proceed triaxial unloading creep tests under different confining pressures and water pressure(pore pressure),and the chamber triaxial creep test of sandstone was carried out by the unloading load mode of fixed axial pressure and confining pressure.By the result of the creep test,it is told that the creep curve of sandstone has four typical stages:fracture compaction stage,deceleration creep stage,steady creep stage and accelerated creep failure stage.Based on the test results,studied the influence of high stress and high pore pressure on creep deformation characteristics of rock.Through the axial creep result to know the viscoelastic-plastic characteristics of sandstone.There has complex viscoelastic and plastic characteristics in the process of sandstone creep.3)Based on the condition of high stress and high water pressure,a new plastic i-mc element was proposed by using the improved nonlinear mohr-coulomb criterion,which was connected with the typical Burgers model to establish a new nonlinear creep model,so as to better describe the nonlinear accelerated rheological deformation stage in the whole creep process curve.And in view of the deterioration and damage of pore water pressure,based on the above nonlinear constitutive model,a nonlinear creep constitutive model considering the effects of high pore water pressure damage and high confining pressure was established by introducing the damage variables of elastic modulus damaged_E and viscous coefficient damage d_?.The parameters of the rheological model of sandstone sample were identified by LM nonlinear optimal least square method,and the nonlinear damage rheological model was verified by axial creep curve.The results showed that the model was in good agreement with the results of the creep sample,which reflected the correctness and rationality of the model.