化学腐蚀和干湿循环作用下砂岩I型断裂韧度及其强度参数相关性的研究

以三峡库区典型的库岸边坡消落带节理砂岩体的实际赋存环境为背景，采用在砂岩中预制I型裂隙的方法来模拟节理岩体，根据工程实际设计饱水-风干循环试验方案，研究了浸泡在不同化学溶液中的I型裂纹砂岩在干湿循环作用下的力学特性及损伤劣化机理，分析了经不同化学溶液和干湿循环作用后试样的物理力学特性随干湿循环次数的劣化规律。研究结果表明：化学溶液和干湿循环作用后砂岩试样呈现出明显的弱化趋势；试验初期，强碱性溶液下砂岩试样的干湿劣化程度最小，但随着干湿循环次数的增加，强碱性溶液下砂岩试样的干湿劣化程度逐渐加剧，仍小于酸性溶液下的，但大于中性溶液下的。化学干湿循环作用后，砂岩试样各力学特征的损伤劣化程度存在明显的差异，其中断裂韧度K_IC的劣化程度较大，抗拉强度居中，而抗压强度最小。化学干湿循环作用后砂岩的断裂韧度与抗压强度、抗拉强度间存在明显的线性关系。砂岩各力学特征的劣化程度与其相应的化学溶液中溶出离子浓度的大小、试样物理参数的劣化程度之间具有某一对应关系，同时，得到砂岩试样物理力学参数与损伤变量和钙镁离子浓度之间统计上的关联关系。并且，可以利用不同化学溶液和干湿循环作用下砂岩试样的裂纹扩展半径来间接说明其力学特征发生损伤的劣化程度。

Experimental study on mode-I fracture toughness and its correlation with strength characteristic of sandstone under dry-wet cycles

Taking the actual environment of the hydro-fluctuation belt of a typical bank slope in the Three Gorges Reservoir Region as background, by means of prefabricating mode-I cracks in the sandstone specimens, one test scheme of drying-wetting cycles is adopted to explore the mechanical characteristics and damage degradation mechanism of mode-I sandstone specimens immersed in different chemical solutions. The variation regularities in the physical and mechanical prosperities were analyzed under the effects of chemical solutions and drying-wetting cycles. Experimental results show that sandstone specimens have a significant damage deteriorating trend under effect of chemical solutions and drying-wetting cycles. In the first 0~1 drying-wetting cycles, the degradation degree of sandstone specimens immersed in alkaline Na₂SO₄ (pH=12.0) solutions is the smallest, however, its damage degree in Na₂SO₄ (pH=12.0) solutions gradually increased with the increasing of F-T cycles,but it is still less than that in the acid Na₂SO₄ (pH=3.0) solution and was greater than that in neutral Na₂SO₄(pH=7.0) solutions. There is a difference in the damage deterioration degree of mechanical properties under effect of chemical solution and drying-wetting cycles, that is, the damage deterioration degree of fracture toughness K_IC is the greatest, that of compression strength is the smallest. Meanwhile,there are obvious linear relationship among fracture toughness K_IC,compression strength and tensile strength under the effects of different chemical solutions and drying-wetting cycles. Meanwhile, there are also obvious consistency relationship among the damage degree of mechanical proprieties,its damage degree of physical proprieties and the ions concentration dissolved in the corresponding chemical solution. Therefore, the correlation relationships among physical and mechanical proprieties of sandstone, damage variables and the ions concentration of calcium and magnesium are obtained. The crack propagation radius can be used to indicate the damage deterioration degree of mechanical proprieties under chemical solutions and drying-wetting cycles.