| The geological environment of the long-large-deep buried tunnel engineering in western of China is very extreme and unusual. For example, the Water diversion tunnel of western route of water diversion from South to North, whose buried deep is 1100 m, has as high as 50 MPa for the maximum principal stress and the local ground temperature of surrounding rock of this tunnel can be as high as 70℃; For Motuo Hydropower Station, which is in the planning of the yarlung zangbo river,the long Water diversion tunnel, whose length is 40Km, maximum depth is 4000 m, the value of gravity stress is about 108 MPa and the surrounding rock ground temperature will be above 90℃, will be built;Under the coupled action of high ground stress and high ground temperature, the sudden geological risk of tunnel engineering poses a great threat to the safety of the deep buried project. In this paper, we base on the railway tunnel project from Dali to Ruili of Gaoligongshan and do some systematic tests and numerical simulations and finally reveal the mechanism of hard rock failure under the effect of thermal-mechanical coupling.In this paper, on one hand, on the base of uniaxial compression tests, triaxial compression tests and strong unloading triaxial test, we study the rock bursting tendency index, the temperature effect of brittle failure and the brittle failure process of rock under the condition of strong unloading. On the other hand, we combine with the method of particles flow numerical simulation to study the rock burst mechanism of hard rock. The main result shows as follow:(1)The results of Uniaxial compression tests under high-temperature showed that when the temperature is 20℃ and 60℃, the destructive type of samples appears type-Ⅱ; When the temperature is 40℃,90℃ and 130℃, the destructive type of samples appears type-I. The tests results of rock bursting tendency indexes show that the low and medium rock burst is in the transition to the intense rock burst, when temperature is in the range of 20℃-60℃.60℃ is the critical temperature for the tendency index of the rock bursting, but the tendency index gradually reduces as the temperature is beyond 60℃. Through the uniaxial test at high-temperature, we study the temperature effect of hard rock based on the energy released and rock bursting tendency index during the test, the result shows:when the temperature changes in the range of 20℃ to 60℃, the strength of a brittle failure enhances as the temperature rises; When temperature is more than 60℃, the destructive type of the rock changes from brittle fracture to brittle-ductile damage as temperatures continue to rise.(2)The results of high temperature triaxial compression test show that when the temperature is in the range of 20℃-60℃, the higher the temperature is, the brittle the rock will be. When the temperature is beyond 60℃, the destructive type of rock changes from brittle fracture to ductile damage. As the temperature increases, the cohesion increases firstly and then declines, but the angle of internal friction appears as the counter-part. According to the sketches of failure characteristics of rocks, we figure out that under the condition of low confining pressure, the failure characteristics of rocks change from the failure mode of tensile-shear to the failure mode of tensile but under the condition of high confining pressure, the failure characteristics of rocks change from the failure mode of tensile to the failure mode of tensile-shear(3) Based on the deformation characteristic curve and failure characteristics got by the strong unloading triaxial test, we can find that when the temperature is in the range of 40℃-60℃, the stress of brittle rock falls down rapidly as the stress reaches the peak value. The sketch of failure characteristics of brittle rock appears failure mode of tensile-shear. On the surface of rock sample, we can find some cracks caused by the tensile stress and the rock sample appears strongly brittle failure. When the temperature is in the range of 60℃-130℃, because of the effect of temperature, shear stress of rock rapidly increases, the rock failure type change as brittle-ductile type.According to measuring angle of complete failure face, we find that failure angle increases as temperature rises firstly, then decreases. During the process of brittle rock failure test, we find that the cohesion decreases but the friction increases.(4)Through acquisition of strong unloading triaxial test the whole process of acoustic emission events (AE) analysis, the temperature of 40℃ to 60℃ damage when the transient energy is large, compared to other temperature situation, shows that when the temperature of 40℃ to 60℃, the danger of rock damage is high, which means the possibility of a strong rock burst is much more than other high temperature.By analyzing fracture scanning electron microscopy (SEM), the temperature falls below 60 ℃ when rock failure to shear fracture, but the tensile damage percentage is higher, belongs to brittle fracture, fracture form belongs to a kind of low energy absorption. Due to along the cleavage crack will consume the least strain energy, macroscopic failure mode is shown as sudden-sudden instability. When temperature above 60℃, fracture performance of shear fracture characteristics, but at the moment, shear failure of main columns, macroscopic failure mode is subject to sudden instability.(5)Through flow numerical simulation study, compared with macro mechanical test results are consistent, failure characteristics with the temperature rise to shear failure, when the temperature of 40 "C, rock microscopic fracture is the most intense, the stress drop value maximum, instantaneous release energy than other high temperature, and the tensile crack quantity is more, damage form is mainly a cracks caused by shear damage, high possibility of rock burst. And when the temperature is greater than 40℃, the tensile cracks still occupy absolute proportion, but in comparison, less damage. |
