水化学溶液对灰岩力学特性的影响分析

Influence of aqueous solution on mechanical properties of limestone

采用蒸馏水及pH=2溶液对灰岩浸泡80 d后开展单轴及三轴压缩试验,研究不同溶液对灰岩力学特性的影响规律,并采用扫描电子显微镜(scanning electron microscope,SEM)观察浸泡前、后灰岩微观形态的变化特征,同时结合灰岩微观结构特征分析水岩作用对灰岩力学特性的劣化机制。试验结果表明:蒸馏水和pH=2溶液均与灰岩发生了化学反应,浸泡溶液中溶蚀有大量的Ca^2+、Mg^2+、Fe^2+(Fe^3+)等阳离子;相同围压条件下,经过蒸馏水与pH=2溶液浸泡80 d后的灰岩试样峰值应力、弹性模量相对于原始试样均有所降低,而泊松比增大,其中pH=2溶液浸泡的试样峰值应力降幅最大,泊松比增幅最高;单轴试验条件下试样表现出剪切破坏、张-剪复合破坏、张拉破坏,而在施加10 MPa围压条件下,试样均为剪切破坏;水溶液浸泡后试样表面发生溶蚀,孔隙增加。此外,水化学溶液对灰岩内部微裂隙的溶蚀和润滑作用也是导致灰岩力学性质劣化的原因。

Uniaxial and triaxial compression tests were carried out on limestone after immersion for 80 days with distilled water and pH=2 solution.The effects of different solutions on the mechanical properties of limestone were studied.Scanning electron microscope(SEM)was used to observe the microscopic morphology of limestone before and after soaking.The variation characteristics,combined with the microstructure characteristics of limestone,were used to analyze the degradation mechanism of water-rock interaction on the mechanical properties of limestone.The test results show that both distilled water and pH=2 solution have chemical reaction with limestone.A large amount of Ca^2+,Mg^2+,Fe^2+(Fe^3+)and other cations are dissolved in the soaking solution.Under the same confining pressure condition,the peak stress and elastic modulus of the limestone sample after soaking for 80 days in distilled water and pH=2 solution were lower than the original sample,but the Poisson’s ratio was seen increased.Among them,the drop of peak stress of the sample soaked in pH=2 solution was the largest,while its Poisson’s ratio increased mostly.Under the uniaxial test conditions,the specimens exhibited shear failure,tensile-shear coupling failure and tensile failure.The specimens were shear fractured under 10 MPa confining pressure.After the aqueous solution immersing,the surface of the sample was dissolved and the pores increased.In addition,the dissolution and lubrication of the micro-cracks in the limestone by the water chemical solution was also the cause of the deterioration of the mechanical properties of the limestone.