Study On Conventional Triaxial Mechanical Behavior Of Granite Undercyclic Stress And Temperature

At the present stage,China has established a complete set of clean energy manufacturing industry chain of hydropower,wind power,nuclear power and solar power,but there are still some problems in the process of new energy power grid connection,nuclear waste disposal and dry hot rock resource development.These engineering or engineering mainly occurs in underground rock mass structure,the surrounding rock mass usually experience cycle for the combined action of temperature,cyclic stress and stress the need to refine the upper limit of temperature and cyclic stress,three to the stress state of rock in the physical and mechanical properties were studied,summed up the rock under the action of alternating stress and temperature of the mechanical properties,to provide theoretical basis for the engineering stability of underground rock engineering long-term.This article around the underground rock-mass engineering with high confining pressure,temperature and stress frequently transform this characteristic,has carried out the real-time temperature,circulating temperature rock damage test,the thermal damage of conventional triaxial compression test,the conventional triaxial cyclic stress and temperature fatigue damage under the condition of experiment,and combining theoretical analysis with test data,the study of the change of the mechanical properties of rock mass of underground engineering.The main research conclusions are as follows:1.With the increase of temperature gradient,the rock mass loss rate increases continuously,and the mass loss process can be divided into three stages:physical water dissipation,chemical water dissipation and debris spalling;At the same time,the volume expansion rate of rock keeps increasing,which is mainly caused by thermal expansion and thermal crack of mineral inside rock.The density of the rock gradually decreases,and the rock becomes "brittle" at extremely high temperatures.The decrease of wave velocity is the most obvious and can better characterize the temperature damage of rock,which can be used to characterize the damage variable.2.The mass and volume of granite samples decrease with the increase of cycle temperature,but different loss processes occur when the temperature is above and below 600?.For the volume and density,the changes mainly occurred in the first temperature cycle and remained unchanged in the subsequent cycles.It is believed that the change of rock volume is the core factor leading to the decrease of density.The P-wave velocity decreases with the increase of the number of cycles.When the temperature is below 500?,the P-wave velocity decreases mainly in the first cycle.When the temperature is above 600?,the wave velocity decreases gradually in the first nine cycles and finally becomes stable.3.The confining pressure has a strengthening effect on the mechanical properties of rock,but there is a phenomenon of diminishing marginal effect.While the elastic modulus increases with the confining pressure in the form of lower concave type,straight type and upper concave type,respectively,corresponding to the rock thermal damage degree from low to high,it can be considered that the rock mechanical properties in low thermal damage-high confining pressure>low thermal damage-low confining pressure,high thermal damage-high confining pressure>high thermal damage-low confining pressure.4.According to the mechanical characteristics of granite in the cyclic stress-temperature test,the change of rock can be divided into "hardened" rock sample and "damaged" rock sample.The mechanical properties of hardened rock samples are enhanced with the increase of the number of cycles,but to a certain extent.The whole process of cyclic stress of damaged rock samples have three stages:initial deformation stage,constant deformation stage and accelerated failure stage.The fatigue life of damaged rock samples is related to the upper stress level,and the higher the stress level is,the shorter the fatigue life is.The lower the stress level,the longer the fatigue life.5.Cyclic stress,temperature and confining pressure have superposition effect,among which,the damage caused by cyclic stress and temperature to rock is the main factor to change the mechanical properties of rock,while confining pressure can strengthen the integrity of rock and is a secondary factor to change the mechanical properties of rock.By comprehensive comparison,the influences of cyclic stress,cyclic temperature and confining pressure on the mechanical properties of rock decrease successively.