Research Of Uniaxial Compression And Creep Experiments Of Sandstone Including Non Coplanar Intermittent Prefabricated Cracks

With west development, the west-to-east gas diversion project and the south-to-north water diversion project carried out, national major infrastructure construction is at an unprecedented rate in China, and most of these major projects are geotechnical engineerings.However, due to the occurrence of rock mass itself has many defects such as joint, cranny, bedding, etc, the stability of rock mass engineering becomes very complicated.Therefore, the safety and long-term stability of the rock mass engineering has become an important scientific problems of engineering and academic research.In order to study the long-term stability of the rock mass containing defects such as cracks, intact sandstone and intermittent precast fractured sandstone were tested based on the National Natural Science Fund Project(No. 41172243) of my tutor: Research of Rheological Properties and Aging Extension Mechanism of Hard Rock with High Residual Stress under Unloading.The tests contain the uniaxial compression test, the creep test under constant load, the creep test under cyclic loading. And the test results were compared and analyzed. In this paper, the main research contents and results are as follows:① Based on the uniaxial compression tests of intact sandstone and intermittent precast fractured sandstone,the fracture extension condition of rock mass with different fissure angle was analyzed, and the macro penetration mechanism was studied. The stress-strain curves of non-coplanar intermittent precast fractured sandstone and intact sandstone were compared. The influences of fissure angle to the rock deformation and strength were analyzed. The relationship between hoop strain and axial strain was discussed. The volume expansion effect of rock mass with different fissure angle was considered. The study found that with the increase of crack angle,the coalescence mechanism of rock bridge of non-coplanar intermittent precast fractured rock mass veried from tensile coalescence to shear coalescence and tensile-shear coalescence, the peak strength, peak strain, poisson’s ratio showed a trend of increase, and the size of elastic modulus equals. Only the intact sandstone’s volume expanses and non-coplanar intermittent intermittent precast fractured rock mass in the whole process from start loading to failure volume has been in a state of compression.② Uniaxial creep tests under constant load of intact sandstone and intermittent precast fractured sandstone were operated. The creep curves of intact sandstone and intermittent precast fractured sandstone under constant load were gained. The axial creep curves and hoop creep curves were analyzed. The characteristics of the creep curves and the creep rate curves of each sample were studied. The influences of fissure angle to the creep and creep rate were discussed. The relationship between attenuation creep rate and time was obtained, and the influences of fissure angle and load to each parameter were analyzed. Research has shown that for intact sandstone sample, with the increase of axial stress, the axial instantaneous strain, axial creep stability time, axial steady-state creep rate, hoop instantaneous strain,hoop creep deformation,hoop creep stability time,hoop steady-state creep rate increase,but the axial creep deformation decrease.For non coplanar intermittent precast fractured rock mass, with crack angles increasing, the instantaneous axial strain, the total axial creep and instantaneous hoop strain increase, but the the total hoop creep deformation decrease.In the stage of creep rate attenuation, creep rate and time can be proposed synthetic form a power function, 1neA t-=,when the creep load equals, constant A and n increases with the crack angle;when the crack angle equals, constant A decreases with the increase of load, and constant n increases with the increase of load.③ Creep tests under uniaxial cyclic loading of intact sandstone and intermittent precast fractured sandstone were operated. The creep curves under uniaxial cyclic loading of intact sandstone and intermittent precast fractured sandstone were obtained, and so were the stress-strain hysteresis curves. The characteristics of each curve were analyzed. The relationship between the irreversible deformation and the cycle number of each sample was studied. The energy mechanism of intact sandstone with cyclic creep was discussed.The creep under dead loading and the creep under cyclic loading were compared. Studies have shown the axial stress-strain curve of the intact sandstone under cyclic loading shows a dense- sparse- dense form. the axial stress-strain hysteresis curve of 35 ° fractured rock mass is denser and denser with the increase of cycle number, hysteresis ring area is smaller and smaller, coincidence degree is higher and higher. The creep deformation of 35 ° fracture rock mass under the cyclic loading is smaller than the creep deformation under low and high dead load.I guess that the effects of rock mass under long cycle cyclic load and short cycle cyclic load are different, there may be a critical period, when the period is lower than the critical period, cyclic load causes a fatigue damage to the rock mass, when the period is higher than the critical period, the effects of rock mass under long cycle cyclic load is better than the long-term dead load with the close value of stress.