Research On The Damage Model Of Rock Under Geothermal-Hydraulic-Mechanical Coupling

In China,there are many infrastructure constructions such as the deep mining of mine,construction of underground works,the storage of nuclear waste and the development of geothermal resources.The high temperature,high hydrostatic pressure and high stress are the most common problems in rock mass engineering.The mechanical properties of rock mass in the high temperature,high hydrostatic pressure and high stress are different,and then it can affect the design,construction and the late completion of the safety of rock mass engineering.In this thesis,this study aims to investigate the damage constitutive model of rock.Tasks of the project are:to establish damage constitutive model of rock under THM coupling;to discuss the mechanical properties and damage characteristics of rock under THM coupling;to prove the correctness of the model by experiments.The main research work and conclusions of the paper are as follows:(1)Based on the definition of damage,thermal damage variable D_T and bearing damage variable D_m are proposed.According to the strain equivalence principle,the relationships between damage variables of rock under coupling is deducted.The thermal damage and stress damage variables evolve respectively by the basic hypothesis of rock mass.The rock mechanics model is established under the THM coupling based on Lemaitre equivalent strain theory,Mohr-Coulomb strength criterion,generalized Hooke's law and bandis model,and the model parameters were determined.(2)The mechanical characteristics of granite under THM coupling are analysised through the triaxial compression test of granite on certain confining pressure and different heat treatment temperature and different pore water pressure.The test results are as follows:the compressive strength of rock decreased gradually with the increase of pore water pressure under the action of temperature;pore water pressure has little effect on the modulus of elasticity,and the amplitude variation can be neglected;maximum strain of rock decreases gradually and the mechanical properties of granite transform from ductility to brittle transition gradually with the increase of pore water pressure.The compressive strength of rock increased first and then decreased with the increase of heat treatment temperature under the effect of pore water pressure,and400?is the peak temperature of granite.The elastic modulus decreases and the maximum strain increased gradually with the increase of heat treatment temperature,and rock properties transform from brittle transformed to ductility gradually.The temperature damage threshold of granite is 400?.(3)The rock damage constitutive model under THM coupling is verified by triaxial compression test,and the model can better reflect the stress-strain relationship of rock under the thermo-mechanical coupling and hydro-mechanical coupling,and it can fully show the initial crack of rock pressure dense stage,elastic stage,damage generation and expansion stage of stress-strain characteristics,and it can fully reflect the changes of the mechanical properties with the changes in external conditions.At the same time,the damage characteristics of granite under the coupling action are studied,and the results are as follows:granite damage increased gradually with the increasing of temperature under the conditions of different pore water pressure;under different heat treatment temperature,granite damage by load remained constant at the beginning,and then gradually increased and with the increase of axial strain,damage variable curve has slowed down;the total damage of granite in THM coupling is effected by heating treatment temperature,and the higher the temperature,the higher the initial injury.It increases gradually with the increase of axial strain and tends to1.0 finally.