Study On The Constitutive Model And Rheological Properties Of Sandstone Damage Under High Stress

Surrounding rocks of deep engineering are in a complex mechanical environment of "three highs and one disturbance",especially deep buried chambers such as coal mines,metal mines,underground storages,etc.,which have problems such as long service life,large cross sections,and difficult maintenance.The mechanical characteristics and mechanical behaviors of the surrounding rock such as damage evolution,energy conversion,creep deformation and failure characteristics under different stress paths are studied.It has important theoretical significance for practical engineering.Through laboratory triaxial compression experiments and triaxial creep experiments,the stress-strain curves of rocks under different stress paths are obtained.Furthermore,a constitutive model can be constructed,and deformation characteristics and energy evolution laws can be analyzed.Based on the creep test of a single specimen,the degradation properties of rheological parameters and strength parameters under the dual effects of stress and time were studied.By introducing the product of overstress difference and time,a new type of unsteady creep constitutive model and stress relaxation model are constructed.In the creep test of a single test piece,the creep parameters are also deteriorated under the effect of time.By introducing Perzyna viscoplastic model and energy dissipation rate,a model that can describe accelerated creep deformation is constructed.Furthermore,the control threshold for accelerated creep initiation can be better defined.By using damage theory and energy theory to explore the deformation and rheological failure mechanism of surrounding rocks,the internal relationship between damage,energy and deformation of surrounding rocks is revealed,and the theoretical basis of qualitative analysis of surrounding rock in deep engineering is improved.After experimental research combined with theoretical model analysis,the following research results are obtained:(1)The deformation failure form of the unloading test is a sudden increase and volume expansion form,while the deformation failure form of the loading failure test is a compression shear form..(2)After the pores in the rock are compacted,the rock is not damaged during the elastic deformation stage.Therefore,the damage variable of the rock at this time is equal to zero.During the deformation stage between the unloading point and the peak point,with the creation of new cracks inside the rock,the microstructure destruction is more intense and the crack development is more complete.This makes the degree of damage to the rocks more severe.At the strain softening deformation stage and the residual deformation stage,the rock is completelydestroyed.This process is basically consistent with the actual damage evolution of the rock,and corresponds to the various stages of the stress-strain curve deformation of the rock.(3)The smaller the unloading amount is,the greater the level of deflection stress required for stable creep deformation is,which indicates that the increase of the unloading amount accelerates the deformation and failure process of the rock sample.Under the action of the last-level failure stress level,the rock specimens experienced a long period of decay creep and stable creep before entering the accelerated creep deformation stage.In the end,the rock's creep deformation exceeds the limit deformation state,and then the rock will fail.(4)Under the dual influence of overstress difference and time,the reduction of the internal friction angle of the rock is much smaller than that of the cohesion.Therefore,in the support design of the surrounding rock of the roadway,the cohesion should be considered in the long-term stability design.(5)The established creep deformation model considering the dissipation rate to accelerate the creep deformation has a high degree of fit under low stress.Under the last-stage failure load,although the model curve and test curve fit are high,there is also a significant deviation in the local,especially accelerated creep deformation stage.It is generally verified that it is feasible to establish a constitutive model of accelerated creep based on dissipative theory,and the model can truly reflect the creep deformation law and stress state of rocks.At the same time,the model can be applied to the description of rock creep characteristics under any kind of conditions,and it has guiding significance for solving the long-term stability of surrounding rock in practical engineering.