水化学与冻融循环共同作用下砂岩细观损伤与力学性能劣化试验研究

Meso-damage and mechanical properties degradation of sandstone under combined effect of water chemical corrosion and freeze-thaw cycles

为研究水化学与冻融循环共同作用下岩石的细观结构损伤及力学性能劣化特征,分别对经酸性、中性和碱性水化学溶液浸泡和冻融循环处理后的砂岩进行核磁共振测试和单轴压缩试验,分析砂岩孔隙度和力学参数的变化规律,结果显示:随水化学溶液浸泡时间的增加,砂岩强度和弹性模量均有所降低,且酸性溶液下的降幅最大。随水化学溶液冻融循环次数的增加,砂岩强度和弹性模量均有明显降低,且中性溶液冻融循环下的降幅最大;水化学溶液浸泡对砂岩小孔径孔隙度分量影响不大,而水化学溶液冻融循环对其影响显著,且不同溶液下小孔径孔隙度分量增幅较接近;水化学溶液浸泡与水化学溶液冻融循环对砂岩大孔径孔隙度分量的影响均较显著,单纯浸泡下酸性溶液增幅最大,冻融循环下中性溶液增幅最大;水化学溶液冻融循环条件下砂岩小孔径孔隙细观结构以受冻胀损伤为主,大孔径孔隙则受化学腐蚀和冻胀损伤的共同作用,在孔隙度上综合表现为冻胀与腐蚀的叠加效应,且在砂岩大孔径孔隙细观结构上,酸、碱腐蚀对其与冻胀作用的叠加效应有一定抑制作用;砂岩初始裂隙体变与核磁孔隙度变化率相关性良好。

The aim of this study is to investigate the meso-damage and degradation mechanism of sandstone under the combined effect of water chemical corrosion and freeze-thaw cycles. Nuclear magnetic resonance(NMR) and uniaxial compression tests were conducted on the sandstone treated by acidic, neutral and alkaline solution immersion and freeze-thaw cycles, respectively. The variations of porosity and mechanical parameters of sandstone were analysed. With increasing immersion time in hydro-chemical solution, the strength and elastic modulus of sandstone decrease, and the maximum decrement occurs in specimens immersed by the acidic solution. With the increase of freeze-thaw cycles, the strength and elastic modulus significantly decrease, and the maximum decrement occurs in specimens immersed by the neutral solution. The porosity component of a small pore is trivially affected by water chemical corrosion, but significantly influenced by the freeze-thaw cycle. Moreover, the increase of small pore size porosity component in different solutions is close to each other. Both soaking and freeze-thaw cycle in hydrochemical solution greatly impact on the large pore-size porosity components of sandstone. Chemical corrosion has the greatest effect on the sandstone in acid solution, while the neutral solution largely affects the specimen under the interaction of chemical corrosion and freeze-thaw erosion. Under the condition of freeze-thaw cycle of hydrochemical solution, the micro-structure of small-pore sandstone is mainly damaged by frost heave, while that of large-pore sandstone is mainly damaged by chemical corrosion and frost heave. In terms of porosity, the superposition effect of frost heave and corrosion is manifested comprehensively. In the micro-structure of large-pore sandstone, the superposition effect of acid and alkali corrosion on the meso-structure of large-pore sandstone and frost heave is restrained to a certain extent. There exists a good correlation between initial fracture volume change and nuclear magnetic porosity change rate.