The Research On Strength And Deformation Characteristic And Strength Criterion Of Deep Underground Rock

Deep underground rock is in complex geological environment. The influence of high temperature and high pressure on rock strength and deformation has great different from the rock on the surface. Combined with the existing data and results, as well as rock uniaxial and triaxial experiments results with the temperature and confining pressure coupling effects, analyzes the strength and deformation characteristics. Then the relationship between the deformation and temperature and confining pressure is discussed. Add the temperature factor into index strength criterion. Then the new rock strength criterion is gained, which was able to reflect the temperature and confining pressure coupling effects. The main research contents and conclusions are as follows:(1)Through the analysis of the mineral rock of T3x2, lithological and physical characteristics are obtained, such as rock mineral composition, content, porosity, permeability coefficient and so on. Therefore, T3x2 rock is a kind of dense quartz sandstone. Combined the rock sample acoustic emission experimental results with the tectonic evolution of this region, we find there are at least 4 times large tectonic movements in geological history, respectively corresponding to middle Indosinian to late Indosinian, early Yanshanian to middle Yanshanian, late Yanshanian to early Himalayan and middle Himalayan to late Himalayan. And the value and orientation of each period tectonic stress is obtained. Researchers had studied the fluid inclusions characteristics. According to the analysis results, such as types uniform tempeture and composition, Xujiahe gas reservoir could be divided into three gas filling stages and the geothermal temperature could be estimated. According to the logging data, the relationship between the strata pressure and temperature and strata depth are obtained.(2)According to the analysis of stratum pressure and temperature, we do the uniaxial and triaxial tests of dense quartz sandstone T3x2 under the coupled temperature and confining pressure. At the same temperature condition, the rock peak strength increases gradually with confining pressure increasing. And the corresponding strain increases, too. At the same confining pressure, the peak strength increases with the temperature by a small margin. And the temperature effect on rock strength gradually increases. The greater the confining pressure, the influence of temperature on the rock strength is obvious. Elastic modulus changes with temperature and confining pressure fluctuatedly, but shows an increasing trendency. The influence of confining pressure on rock strength is larger than temperature.(3)With the increasing of confining pressure, rock failure forms changes from tensile failure to shear failure. When confining pressure is low, rock is tensile failure with many vertical fissures, accompanied by several transverse fissures, and there are many small secondary fissures on the main failure surface. Rock sample is cut into multiple strip rock blocks. When confining pressure is high, the main failure surface is shear plane. The higher the confining pressure, the better the shear surface flatness is. Extrusion and friction are strongly. Scratch is obvious. And there are lots of gray mineral rock flour, which is satiny. The secondary fissures on the main failure surface are less, but its exposed trace on the sample surface the master has many secondary branch fissures on the exposed trace of the sample surface. Under the condition of high confining pressure in low temperature, samples with horizontal bedding will produce a larger plastic deformation.(4)According to the uniaxial and triaxial rock tests with the temperature and confining pressure coupling effects, we elaborate the failure characteristics and cracks on detail. According to the stress-strain curve of each sample, the rock deformation and failure process is analyzed, including pore and fissure pressure stage, elastic deformation stage, micro crack evolution to the accelerated development stage, the stress dropping stage and after failure stage. At the same time the energy evolution during the rock deformation and failure process is analyzed. Rock deformation and failure types could be divided into 5 categories according to the rock deformation process differences at the different temperature and different confining pressure. TypeⅠpre-failure stress-strain curve has two phases-pore and fracture compaction phase and elastic deformation phase. TypeⅡhas three phases-pore and fracture compaction phase, elastic deformation phase and micro cracks extension phase. Type Ⅲ has two phases-elastic deformation phase and micro cracks extension phase. This type of rock yield stage is shorter. The pre-failure stress-strain curve of Type Ⅳ is similar to Type Ⅱ.But Type Ⅳ rock yield stage is larger and gentler. The pre-failure stress-strain curve of TypeⅤ is similar to Type Ⅲ. But TypeⅤ rock yield stage is larger.(5)Considering the temperature and confining pressure coupling effect on rock strength, I improve the index of strength criterion, adding the equation related to the temperature. The parameters of the new improved index criterion have specific physical meaning, which can be obtained through the indoor experiment or experience. Comparing calculation values and experimental values, verification results have optimized effective.