Experimental Study And Numerical Simulation On The Effect Of Water On Rock Mechanical Properties

The long-term response and stability of rock mass engineering structures,such as tunnels,slopes,nuclear waste treatment,geothermal,oil and gas exploitation and even ancient stone relics,have always been concerned,and the rheological properties of rocks are an important indicator for predicting the long-term stability of rock mass engineering.Rock mass structures are often affected by various loads and surrounding environment during long service.There are many cases of engineering instability caused by water and rock action,which indicates that water has an important influence on the safety and stability of rock mass structure.Therefore,it is necessary to fully understand the influence of water on the mechanical properties of rocks,especially the creep properties.However.the law and mechanism of the influence of water on the instantaneous and creep properties of rocks are not clear and sufficient.In view of this,this project intends to carry out research work by combining a large number of physical tests,data analysis and numerical simulation,and apply the test results to explore practical engineering problems.The research conclusions of this paper will be helpful to clarify the law and mechanism of water's influence on rock rheological properties,enrich and perfect the research of rock rheological theory,and provide reference for predicting the long-term stability and safety of rock engineering.The specific work and main conclusions are as follows:(1)Uniaxial compression test,Triaxial compression test and Brazilian split test were carried out on the effect of moisture content on instantaneous mechanical properties of red sandstone.The effects of water content on the uniaxial compressive strength,characteristic stress,triaxial strength,tensile strength and other mechanical parameters of red sandstone are analyzed comprehensively.The results show that the compressive strength,tensile strength and the characteristic stress of each stage of red sandstone decrease in a negative exponential form with the increase of water content,and the strength softening coefficient increases with the increase of confining pressure.With the increase of water content,the failure mode of the sample gradually changed from splitting failure to shear failure.(2)A set of environmental test chamber was designed,which can be used with RMT-150C testing machine.Uniaxial multi-steps loading creep test under the combined action of load and water was carried out for the immersed specimens,and uniaxial compression creep test as contrast tests was carried out for the dry and saturated specimens with surface seals.By distinguishing instantaneous strain,time-dependent creep strain and total strain,the new percentage variable ? is defined as the ratio of creep strain to total strain.The relationships between transient strain,creep strain,steady state strain rate,variable ? and stress are established.The variable ? tends to decrease first and then increase with the increase of stress,In addition,through the conventional Uniaxial,Triaxial and Brazilian splitting creep tests of red sandstone,it is also found that the variable ? tends to decrease first and then increase with the stress.It is considered that the stress at the minimum ? can be used as a new method to determine the long-term strength of rock.The results show that the time-dependent strain and steady-state strain rate increase,the failure time is shorter,and the long-term strength decreases,when compared with the dry and saturated specimens with surface seals.(3)Uniaxial compression creep tests were carried out on unsaturated red sandstone specimens(0%,2.97%,3.34%,3.37%,3.45%)under submerged conditons.The relationship between instantaneous strain,creep strain,steady state strain rate and failure time and initial moisture content was established,and the influence of initial water content on the creep mechanical parameters of red sandstone was analyzed.The results show that under the action of constant load and water,the creep behavior of the initial saturated rock sample still changes significantly.Instantaneous strain and steady state strain rate increase exponentially with the increase of moisture content,while creep strain and failure time decrease with the increase of moisture content.(4)Based on the water absorption test results of the damaged red sandstone specimens under the action of 80%high stress level at different times,the variation rules of the water absorption performance of the saturated red sandstone specimens before and after the sustained]oad were compared and analyzed.The relationship between the change of water absorption performance and the damage evolution and crack growth in the creep process was established.Results show that the saturated specimen under the condition of immersion is affected by both load and water.The continuous increase of cracks in the rock leads to time-dependent deformation,which promotes the continuous migration of water in the environment to the new crack tip,and intensifies the stress corrosion effect of water.Therefore,it is an interactive process of stress,moisture transfer,and damage evolution.This is also the reason why the long-term strength of the immersion specimen is less than,but the the strain rate is greater than that of the saturation specimen.(5)Although there is no dispute about the existence of the loosen zone,the current theory of the loosen zone cannot give an accurate physical explanation and theoretical description of the time-dependent formation of the loosen zone.The formation process of the surrounding rock looseness circle in moisture environment is simulated by the numerical calculation method considering the coupling action of stress-water-damage,and the mechanism of time-dependent formation of the surrounding rock loosen zone is discussed.The results show that there are two parts in the loosen zone of surrounding rock in moisture environment:irregular fracture zone caused by stress and regular material weakening zone caused by water migration.The movement of water in the surrounding rock is a time-dependent process along with the weakening of surrounding rock properties.In addition,the influence of whether and when to reinforce the surrounding rock deformation is discussed.Through comparative analysis and calculation results,it is found that timely adopting the waterproof reinforcement scheme can effectively prevent the surrounding rock deformation.