Study On Relevant Experiments And Quantification Of Coupling Strength For Coupled Thermo-Hydro-Mechanical Behaviour Of Saturated Rocks

As the important components of physical geologic environment for rock mass, temperature field, seepage field and stress or strain field are coupled, namely coupled Thermal-hydro-mechanical(THM) behaviour, which is highly non-linear and complex. Over the past twenty years, great advances have been made in the area of THM coupling theory. However, as a rising interdisciplinary subject, there are several shortages in this area. Funded by NSF,this thesis develops the research on several shortages in the area of THM coupling theory.The main efforts, conclusions and innovative results gained can be expressed as follows.(1) From research achievements obtained on coupling mechanisms, mathematical model and test studies, state-of-the-art of studies on thermo-hydro-mechanical coupling in rock and soil mass are systematically reviewed.(2) On the basis of continuity equation, momentum conservation equation, energy conservation equation, and substantial equation, coupled THM governing equations are derivated with giving up the assumption of local thermal equilibrium, adopting thermal elasto-plastic constitutive relation, taking the effect of temperature gradient on groundwater seepage(analogous to Soret diffusion) and the effect of viscous dissipation of groundwater on temperature field of rock mass into account.(3) The porosity test for sandstone was conducted at various temperature level and various effective stress level. The testing results show that the porosity of sandstone decreases with increasing effective stress at the fixed temperature level, following the law of negative exponent. However, at the fixed effective stress level, the effect of temperature on the porosity of sandstone is very small (37.6℃ temperature variation).(4) The permeability test for sandstone was conducted at various temperature level and various effective stress level. The testing results show that the permeability of sandstone decreases with rising temperature and/or increasing effective stress. At the fixed temperature level, both the permeability and hydraulic conductivity of sandstone decrease with theincreasing effective stress, following the law of negative exponent. At the fixed effective stress level, however, the function between hydraulic conductivity and temperature is not a monotone one.(5) According to the analysis on tests results, the effect mechanism of temperature and effective stress on the permeability is put forward. As far as the sandstone adopted, the effect of effective stress on permeability lies in pressure effect of effective stress on pore and throat, and that of temperature lies in aggravating disaggregation of clay mineral with rising temperature and pressure effect of skeleton expansion on throat.(6) The permeability tests for sandstone and granite with a single fracture were conducted in the process of loading-unloading for confining pressure. The test results show that both the permeability of sandstone and that of granite with a single fracture decrease with increasing effective stress, following the law of exponential decay. The permeability sensitivity of granite to effective stress is more stronger than that of sandstone, but the permeability recovery capability of sandstone is more stronger than that of granite. Moreover, for sandstone and granite with a single fracture, there is obvious hysteresis effect for the restitution of permeability in the process of unloading for confining pressure.(7) Based on the collected data, the effect of temperature and pressure on physical properties of rock and groundwater is researched. The effect of temperature is more greater than that of pressure. The high-precision formula between physical properties of groundwater and temperature are presented.(8) On the basis of previous studies, improved pattern of THM coupling is put forward. Ground on different coupling mode, THM coupling mechanism are classified two sorts as mecha...