酸碱度对砂岩力学性质的影响及微观结构研究

借助MTS816伺服机和压汞试验仪,对不同pH值溶液侵蚀后的泥质胶结细砂岩进行单轴压缩试验与压汞试验,研究了酸碱度变化对岩石强度破坏及其弱化规律和微观结构方面的影响。研究表明:①水溶液趋于强酸强碱性,即偏酸性和偏碱性均会导致岩石的力学强度降低,力学强度弱化率最大时pH值分别为6和9;②溶液pH>9继续增大、pH<6继续减小,对岩石力学强度弱化率影响很小;③pH值由6降低到2,岩石的峰值强度由76.94 MPa降低到70.91 MPa,弱化率仅为7.83%;pH值由7增大到10,峰值强度由79.89 MPa降低到64.41 MPa,弱化率为18.12%;pH值由10增大到12,峰值强度由64.41 MPa降低到63.00 MPa,弱化率仅为2.19%;④随着溶液酸、碱性的增大,泥质细砂岩的孔隙度和歪度表现出增大的趋势,其中直径<0.1 μm孔隙所占比例变化最大,也是决定侵蚀后岩石力学强度弱化的微观主要因素。该研究定量地得出酸碱度对岩石力学性质的影响与微观结构的变化规律,为更准确研究隧道及地下工程等涉水的岩石工程领域安全、稳定方面提供了新的思路与方法。

Influence of pH Value on Mechanical Properties and Microstructure of Sandstone

Uniaxial compression test and mercury injection test are conducted on argillaceous cemented sandstone corroded in solutions with different pH values by using MTS816 servo system and mercury intrusion porosimeter. The influences of pH value on strength degradation and microstructure of rock are examined. The results are concluded as follows: (1) acid or alkaline solution both weakens the mechanical strength of rock, and especially when pH value equals 6 and 9, the strength degradation rate reaches the maximum. (2) When pH value reaches 9 and continues to grow, or reduces to 6 and continues to drop, the strength degradation rate is rarely affected. (3) When pH value decreases from 6 to 2, the peak strength of rock declines from 76.94 MPa to 70.91 MPa, with the degradation rate amounting to 7.83%; when pH value increases from 7 to 10, the peak strength reduces from 79.89 MPa to 64.41 MPa, and the degradation rate is 18.12%; when pH value further increases from 10 to 12, the peak strength drops from 64.41 MPa to 63.00 MPa, with a degradation rate only 2.19%. (4) Despite the increase or decrease of pH value, the porosity and skewness of argillaceous fine sandstone tend to rise. The proportion of small opening with diameter less than 0.1 μm experiences the greatest change, and is, meanwhile, the major microcosmic factor that decides the degradation of mechanical strength of the corroded rock. The quantified influence of pH value on the mechanical properties and microstructure of rock would offer new idea and approach for researches on the safety and stability of water-involved rock engineering field.