干湿循环与化学溶蚀作用下玄武岩传质‐劣化过程的试验研究

Experimental study on the mass transfer-deterioration process of basalt under drying-wetting cycles and chemical reaction

库区消落带岩体受持续干湿循环作用,导致岩体风化加剧,力学性质随之劣化。以玄武岩为研究对象,分别开展pH=3,7,11溶液条件下的干湿循环试验,探讨溶液pH值及循环次数作用下玄武岩单轴抗压强度的劣化规律。通过溶液化学成分检测,分析3种pH条件下的水岩传质过程。基于玄武岩溶解动力学机制,研究非平衡态与平衡态时的强度劣化与传质过程。研究结果表明:3种溶液环境下试件单轴抗压强度均随循环次数的增加而降低,不同pH溶液环境中,其劣化效应在前期存在显著差异,酸性劣化程度最大,中性次之,碱性最弱,这种差异性在后期逐渐减小,最终3种溶液环境下的劣化程度相当;酸、碱溶液中的水岩化学反应经历了从非平衡态到平衡态的转变,中性溶液中的水岩化学反应始终处于非平衡态;不同pH值溶液中的非平衡态反应过程一致,玄武岩中元素释放顺序为:Ca,Al,Si,平衡态反应过程中Al在固相表面发生沉淀与置换,沉淀将抑制Si元素的释放,而置换将促进Si元素的释放;中性溶液中的岩石强度劣化程度受控于非平衡态的全等溶解反应,酸性与碱性溶液中,岩石强度劣化在前期受到Al沉淀形成速度的影响,后期受到Al置换作用影响。研究成果可为合理评价玄武岩库岸边坡长期稳定性提供科学依据。

Under the effect of continuous drying-wetting cycles,the rock mass in the water-level-fluctuating zone of reservoir would experience the weathering aggravation and the mechanical properties deterioration.Cyclic drying-wetting tests were carried out under the conditions of pH=3,7 and 11 respectively using basalt samples.The degradation laws of uniaxial compressive strength of basalt under different pH and cycles were discussed.Chemical composition of solution were tested to analyze the mass transfer between solution and rock.Based on the basalt dissolution kinetic theory,the effect of reaction processes on strength degradation were studied.The results showed that the uniaxial compressive strength decreases with the increase of cycles in all of the three solutions.While there were significant differences in the decline level during the early stage.Acid condition exhibited the most severe corrosion impact on strength,neutral the moderate,alkaline the least.In the mid-late stage,the difference was minimized.The final deterioration level was almost the same in three solutions.The water-rock reaction in acid and alkaline condition underwent a transition from non-equilibrium to equilibrium.In neutral condition it was always in non-equilibrium state.The elements releasing order in non-equilibrium process under different pH condition obeyed the same rule,which were Ca the first,Al the second,and Si the last.In equilibrium reaction,precipitation and replacement of Al occurred on the solid phase surface.Precipitation would inhibit the release of Si,while replacement would promote the release of Si.The deterioration degree of rock strength in neutral solution was controlled by the stoichiometric dissolution in non-equilibrium state.In acidic and alkaline solutions,the strength degradation of rock was affected by the formation rate of Al precipitation in the early stage,and the replacement of Al in the later stage.The research results could provide scientific basis for evaluating the long-term stability of reservoir slope in basalt area.