干湿循环作用下红砂岩动态拉伸力学性能试验研究

Experimental study on the dynamic tensile properties of red-sandstone after cyclic wetting and drying

为研究干湿循环对岩石动态拉伸力学性能的影响,利用φ50 mm分离式霍普金森压杆(SHPB)试验系统,对红砂岩试样进行动态巴西圆盘试验。结果表明:干湿循环对红砂岩动静态抗拉强度有明显的劣化作用,动静态抗拉强度随干湿循环次数的增加逐渐降低;在不同加载速率条件下,经历不同干湿循环次数后的红砂岩试样均存在一个临界加载速率bσ&;当加载速率小于bσ&时,红砂岩动态拉伸强度随加载速率的增加而提高,当加载速率超过bσ&时,红砂岩动态拉伸强度基本保持不变;加载速率相同时,红砂岩动态拉伸强度随干湿循环次数的增加而逐渐下降,下降速度先快后慢。不同干湿循环次数后红砂岩破碎块度分形特征明显,分形维数为2.46~2.81,分形维数与加载速率呈对数增长关系。综合考虑干湿循环次数与加载速率的共同影响,给出了红砂岩动态拉伸强度的计算公式,可为岩土工程相关设计参数提供理论依据。

In order to investigate the influence of cyclic wetting and drying on the dynamic tensile strength of rock,a series dynamic Brazilian disc tests on red-sandstone were carried out through split Hopkinson pressure bar（SHPB） apparatus with a diameter of 50 mm. The laboratory test results indicate that cyclic wetting and drying have a strong deterioration effect on the static and dynamic tensile strength and that the static and dynamic tensile strength both decrease with the increasing of the number of cycles. Under the different conditions of loading rate,all specimens（the times of wet-dry cycles as the variable） have a critical loading ratebσ. When the loading rate is below σb,the dynamic tensile strength increases with the increasing of loading rate. While the dynamic tensile strength remains unchanged when the loading rate is above σb. When the loading rates are the same,the dynamic tensile strengths decrease with the increasing of the number of wet-dry cycles,and the decreasing rate appears quickly initially and slowly later. There is an obvious fractal feature of red-sandstone fragment after different wet-dry cycles,ranging from 2.46 to 2.81 of the fractal dimension,The relationship between the fractal dimension and loading rate is logarithmic. An empirical equation considering the combined effect of the wet-dry cycles and loading rate is established to calculate the dynamic tensile strength of red-sandstone.