Study On Resistivity Of Hydrochemical Corrosion Granite Under Thermal-mechanical Coupling Conditions

The rock mass in deep engineering is mostly in the environment of high ground temperature and high ground stress.In addition,the chemical ions in groundwater erode some rock minerals,which changes the mineral composition and structure of the rock,not only leads to the change of its mechanical properties,but also reflects the conductivity of the rock mass.Resistivity is an important parameter to characterize the conductivity of rock mass.Understanding the relationship between resistivity and mechanical parameters of rock mass is of great significance for the detection and evaluation of engineering rock mass.In this thesis,considering the high pressure and high temperature conditions of deep ground engineering,the resistivity characteristics of chemically corroded granite under thermal-mechanical coupling conditions are systematically studied by means of laboratory tests and numerical simulation.The resistivity response mechanism of chemically corroded granite damage process is studied from macro and micro scales.The main results and conclusions are as follows:（1）Based on the occurrence conditions of surrounding rock in deep underground engineering,a high-pressure temperature-controlled rock resistivity test device was developed.The device can obtain the resistivity,temperature,stress and strain information of rock in real time.The maximum bearing capacity is 600 k N,the confining pressure is 80 MPa,and the maximum working temperature is 80°C.（2）The results of X-ray diffraction（XRD）and low field nuclear magnetic resonance（NMR）show that the granite used in this experiment is mainly composed of Quartz（Si O₂）,Albite（Na Al Si₃O）,Biotite(KFe Mg₂(Al Si₃O₁₀)（OH）₂),and Calcium Feldspar(Mg₂Al₄Si₅O₁₈).Acid solution（p H=1）mainly erodes Albite,Biotite and Calcium Feldspar.The porosity of granite with different corrosion degrees is 0.705%（uncorroded）,0.765%（corroded for 30 days）,1.105%（corroded for 60 days）,1.395%（corroded for 90 days）,and the pores are mainly micropores and mesopores with a pore size range of less than 1μm.（3）The resistivity test of water chemical corrosion granite under different temperature and constant pressure loading and unloading conditions was carried out.The resistivity is positively correlated with the pressure in the loading stage,and the resistivity increases with the decrease of pressure in the unloading stage.The porosity and temperature are negatively correlated with rock resistivity.The significant effects are porosity,temperature and pressure.（4）Based on the Archie formula,a complete rock resistivity model under different thermal conditions is established.The average deviation between the model calculation results and the experimental measured values is 3.29%.（5）In the process of stress damage of corroded granite,the resistivity of granite changes with the deviatoric stress as follows:when the deviatoric stress is less than 10MPa,the resistivity of granite increases with the increase of deviatoric stress,and the longer the chemical corrosion time,the more obvious the increase.Then with the increase of deviatoric stress,the resistivity decreases,and the resistivity of rock increases sharply after the specimen is destroyed.The resistivity values of granite with different degrees of hydrochemical corrosion are 50.9%,62.9%,62.6%and 49.1%of its initial resistivity,respectively.After destruction,the resistivity increases to 150～200%of the initial resistivity in a very short time.（6）According to the results of X-ray CT scanning,we concluded that the average porosity of intact granite was only 0.014%,and the average porosity increased to 2.39%after the granite was damaged.After failure,the average width of cracks formed by different cross-section depths of granite is 35.0～56.7μm,and the length of cracks is0.103～3.120 mm.The crack area of different cross-section depths is symmetrically distributed,and the total area of cross-section cracks at Z=11 mm is the largest,reaching1.914 mm².（7）The numerical simulation results show that the resistivity of intact granite is9431.8～3401.5Ω·m under different temperature conditions,and the results are in good agreement with the experimental measured values.The average deviation rate is 5.39%.After the destruction,the resistivity of granite decreased greatly,only 103.1～33.1Ω·m.Under the same temperature gradient,the resistivity of granite before and after destruction decreased by 98.9%on average.There are 104 figures,21 tables and 124 references in this thesis.