冻融循环对麦积山石窟砂砾岩微观结构损伤机制研究

Study on damage mechanisms of the microstructure of sandy conglomerate at Maijishan grottoes under freeze-thaw cycles

冻融循环作用是影响麦积山石窟风化的主要原因之一。通过室内试验分析和研究开放条件下麦积山石窟饱水砂砾岩在3种温度区间(-5℃~20℃,-10℃~20℃,-15℃~20℃)冻融循环作用下的波速损失率、质量损失率和抗拉强度的变化规律;采用CT和数字图像处理技术,分析岩样微观结构特征的变化;引入均化应力概念,将结晶压力与岩石宏观力学性质对比,作为岩石是否发生破坏的判据。结果表明:(1)岩石质量、波速、抗拉强度均与冻融循环次数呈反比,但与冻融循环最低温度呈正比。(2)提出温度区间是岩石冻融劣化的关键性环境控制因素,岩石原始胶结结构的破坏以及形成的孔隙是影响岩石冻融劣化的关键性内在因素。(3)结晶均化应力与岩石屈服强度的对比,能够较好的用于判断冻融作用对岩石损伤的影响,研究结果有望为石质文物冻融风化机制以及相关保护技术的研发提供理论依据。

The freeze-thaw cycle is one of the main reasons affecting the weathering of Maijishan grottoes.The changes of the wave velocity、the mass and the tensile strength of the saturated sandy conglomerate under open conditions due to freeze-thaw cycles are studied through laboratory experiments in 3 temperature ranges of-5℃-20℃,-10℃-20℃and-15℃-20℃,and CT and digital image processing techniques are used to analyze the changes of the microstructure characteristics of the rock samples.The concept of homogenized stress is introduced and compared with the macromechanical properties of the rock as a criterion for whether the rock is damaged.The results show that the mass,the wave velocity and the tensile strength are inversely proportional to the number of freeze-thaw cycles but directly proportional to the minimum temperature of the freeze-thaw cycle.It is proposed that the temperature range is the key environmental control factor for the freeze-thaw degradation of rock,and the destruction of the original cement structure of the rock and the pores are the key internal factor.The comparison between the crystallization homogenization stress and the rock yield strength can be better used to judge the influence of freezing and thawing on rock damage.The research results are expected to provide a theory for the research and development of freeze-thaw weathering mechanisms of stone cultural relics and related protection technologies.