干湿循环作用下红砂岩强度劣化特性试验

为探究库水位周期性涨落条件下，库岸边坡消落区岩体的强度劣化特性及损伤演化规律，以红砂岩为研究对象，通过干湿循环试验模拟库岸边坡岩体的实际赋存环境，以常规单轴、三轴试验为手段，开展干湿循环作用下红砂岩强度劣化特性试验研究，分析干湿循环作用下红砂岩波速等特性的演化规律，定量分析了干湿循环作用对红砂岩强度主要力学参数的影响，并提出了基于黏聚力的损伤变量。结果表明：随干湿循环作用次数的增多，红砂岩的波速逐渐减小，孔隙率逐渐增大，减小和增大的趋势呈现出明显的三阶段特征，红砂岩单轴强度也逐渐减小，对应的峰值应变逐渐增大，其破坏形式为脆性破坏；以波速计算的红砂岩损伤变量表明，损伤变量随干湿循环次数的增多呈非线性增大趋势，可采用幂函数拟合；干湿循环作用下红砂岩黏聚力显著减小，而摩擦角变化不明显，干湿循环作用主要通过弱化黏聚力造成红砂岩单轴强度的降低，单轴抗压强度降低百分比η_1N与黏聚力降低百分比η_2N呈显著非线性对应关系；提出了基于黏聚力衰减的新损伤变量，并通过与波速损伤变量的计算值和试验值的对比验证了该损伤变量指标的合理性。

Experimental Research on Strength Degradation of Red Sandstone Under Dry-wet Cycle Conditions

The purpose of this paper was to explore the strength degradation properties and damage evolution law of the rock mass in the bank slope drawdown areas under the condition of the reservoir water level fluctuation in cycles. A series of uniaxial and trixial compression tests on red sandstone under dry-wet cycles simulating the actual environment of the water back slope rock mass was carried out. The evolution law of physical properties, especially ultrasonic velocity of red sandstone in dry-wet cycles was analyzed. The influence of the dry-wet cycle on mechanical parameters of red sandstone strength was investigated quantitatively. The damage variable on the basis of cohesion was proposed. The results show that the ultrasonic velocity decreases and the porosity increases with the increasing dry-wet cycles. The trend of variation obviously presents three-stage characteristics. The uniaxial strength of red sandstone decreases with the increase of dry-wet cycles, and the corresponding peak value increases gradually, with the form of brittle failure. The damage variable calculated by ultrasonic velocity show that the damage variable of red sandstone increases nonlinearly with the increase of dry-wet cycles. The power function fitting is applicable to analyze the trend. The cohesion decreases obviously but the friction angle remains steady relatively with increasing dry-wet cycles. The dry-wet cycles reduce the uniaxial strength by weakening the cohesive force of red sandstone. The decreasing percent of uniaxial strength η_1N and the decreasing percent of cohesion η_2N have high nonlinear relations. The comparison between test and calculated value indicates the rationality of the proposed damage variable based on cohesion.