| The sandy slate from a hydropower station excavation slope in Lianghekou,Yalongjiang, Sichuan has been fetched in this paper as the research object, and5kindsprecast through joint of0°、30°、45°、60°、90°angle has been made on them. The acousticvelocity test, uniaxial compression test and conventional triaxial compression test wereconducted on the precast joint samples to simulation the strained condition of rock mass indifferent joint angle、confining pressure and unloading rate, and the results are applied toengineering. The main research contents and conclusions are as follows:1) The acoustic velocity test and uniaxial compression test show that with theincrease of the joint angle, acoustic velocity of samples shows an increase trend and aquadratic function can be used to represent the change rule of acoustic velocity attenuationrate along with the joint angle: V0.0000120.00210.1137. The peak strength andelastic modulus of joint samples are less than the intact samples. With the joint angleincreasing, the peak strength and elastic modulus change in U-curve, the minimum appearsin joint samples of60°angle. Gypsum surface appear shear moving in joint samples of45°and60°samples. The others are all brittle failure and failure surface was through the jointsurface.2)The triaxial compression test shows that the samples have more significantcharacteristics of yield with the increase of the confining pressure for the intactsamples.The stress-strain curve model has a big difference under different joint angle; theelastic modulus and deformation modulus of intact and joint samples nonlinearly increasewith the increase of confining pressure level; fitting the relationship between the confiningpressure and the peak strength, Mohr-Coulumb criterion has a higher fitting precision thanthe Hoek-Brown criterion. The destruction of45°to60°joint samples slide along the jointsurface, and the destruction of0°,30°,90°joint samples slide through the joint surface, itshows that damage characteristics of joint specimen is anisotropy.3)The triaxial unloading test shows that the mechanical properties during loadingstage of triaxial unloading test is similar to common triaxial test. During the unloadingphase, the stress of45°and60°joint angle samples is almost constant after unloading, andthe strain has a rapid growth without failure stage, other joint angle samples all have failurestage; deformation modulus decreases continuously with the increase of unloading;deformation modulus has small amplitude decrease when unloading amount is less than 60%, and reduced in nonlinear significantly when unloading quantity is from60%to100%,deformation modulus of the60°angle joint sample has the largest decline. The peakstrength of joint samples in unloading test changed in U-curve and the strength of sampleswith the joint angle of60°is the smallest,90°is the largest. The effect of unloading on thestrength parameters mainly embodied in the reduction of the cohesive force; comparedwith triaxial compression test, there are more cracks and greater damage in unloading test.With the increase of confining pressure level, the destruction form of0°、30°、90°anglejoint sample has a transition from tensile-shear damage to compression-shear damage.45°,60°angle joint samples slide along the joint surface and samples are in good condition;unloading rate has different degrees of influence on strength, deformation and failurecharacteristics on unloading phase of joint samples.4) A two-dimensional finite element calculation has been conducted on a slope inLianghekou hydropower station, using results of triaxial unloading test on joint samples, itshows that the displacement near the excavation surface outside slope is greatly increasedwith the increase of unloading rate and the plastic zone is also expanding. So suggest thatthe influence of excavation scheme on the rock mass unloading rate in the process ofpractical excavation should be considered to ensure the project construction. |
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