冻融循环和干湿循环作用下砂岩断裂韧度及其与强度特征相关性的试验研究

Experimental Study on Fracture Toughness and its Correlation with Strength Characteristics of Sandstone Under Freeze-thaw Cycles and Dry-wet cycles

以三峡库区岸边坡消落带的典型砂岩为研究对象,针对其实际的赋存环境设计了干湿循环和冻融循环2种试验方案,分别研究了2种试验方案过程中砂岩试样的力学特征,分析了浸泡在不同化学溶液中的砂岩试样经历不同循环次数后各力学参数的变化规律.试验结果表明:干湿循环和冻融循环作用下砂岩试样具有明显的"弱化"趋势,其断裂韧度、抗压强度和抗拉强度劣化趋势基本一致,但试样各力学参数的劣化程度却存在差异.其中,断裂韧度KIC的劣化程度最大,抗拉强度次之,抗压强度最小.干湿循环和冻融循环作用过程中砂岩试样各力学参数的劣化程度均非常显著,该现象说明在模拟库岸边坡消落带岩体遭受化学溶液作用时,干湿循环和冻融循环作用均是不可能忽视的影响因素.但比较而言,在冻融循环作用下砂岩试样各力学参数的劣化程度更加显著.不同的化学溶液对砂岩试样力学特征的损伤劣化程度的影响有所不同,酸性化学溶液加剧了砂岩的劣化程度,而SO2-4离子对砂岩劣化的影响大于HCO-3离子的.

According to the actual occurrence environment of the hydro-fluctuation belt of a typical bank slope, two test schemes of dry-wet cycles and freeze-thaw cycles are adopted to explore the mechani- cal properties of the sandstone specimens sampled from the hydro-fluctuation belt of a typical bank slope in the Three Gorges Reservoir Region. The variation regularities of several mechanical parameters of the sandstone specimens immersed in different chemical solutions after undergoing different cycle times are an- alyzed. Experimental results show that the sandstone specimens have a significant weakening tendency un- der dry-wet cycles and freeze-thaw cycles. The degradation trends of fracture toughness, uniaxial compres- sive strength, and splitting tensile strength are basically consistent. However, the deterioration degrees of these mechanical parameters are different, i. e. , the deterioration degree of the fracture toughness Kic is the greatest, followed by that of the splitting tensile strength, and then that of the compressive strength. The degradation degrees of the mechanical parameters of the sandstone specimens under dry-wet cycles and freeze-thaw cycles are significant, which shows that the actions of dry-wet cycles and freeze-thaw cycles cannot be ignored in the simulation for rock mass in the hydro-fluctuation belt of a typical bank slope ex- posed to chemical solutions. Under comparison, the degradation degrees of the mechanical parameters of the sandstone specimens are more apparent under freeze-thaw cycles. Different chemical solutions may have different effects on the mechanical properties of the sandstone specimens, e. g. , strong acid solutions may aggravate the damage deterioration in sandstones; and SO42- ions have a greater effect on the deterio- ration in sandstones than HCO3- ions. Chemical corrosion, together with freeze-thaw cycles or dry-wet cy- cles, can mutually influence and aggravate the degradation and damage of sandstone specimens. The re- search results provide useful knowledge on the stability analysis of the hydro-fluctuation belt of a typical bank slope.