冻融循环下钙质砂岩力学特性及其损伤劣化机制的试验研究

Experimental study on mechanical properties and damage degradation mechanism of calcareous sandstone subjected to freeze-thaw cycles

通过室内试验的方法,研究了水化学溶液和冻融耦合作用下砂岩的损伤劣化机制和物理力学特性。对浸泡在不同的化学溶液条件下的砂岩分别开展冻融循环试验研究,并对不同冻融循环次数下砂岩的物理力学特性进行量测。研究发现:不同水化学溶液和冻融循环耦合作用下,砂岩试样损伤劣化模式不同,2种主要模式为颗粒剥落、片落模式和裂纹模式。强酸性环境下(pH=3.0),砂岩物理力学特性的冻融循环损伤劣化程度最大,强碱性环境(pH=12.0)次之;在中性至弱碱性环境下,其冻融损伤劣化程度虽然有一定的缓解,但仍随着循环次数的增加而不断加剧。Na_2SO_4溶液的浓度越大,砂岩试样冻融系数的降低速率越大;0.01 mol/L NaHCO_3 pH=9.0下砂岩试样的冻融循环劣化程度相对0.01 mol/LNa_2SO_4 pH=9.0下小;岩石的冻融损伤劣化与其所处的水化学环境密切相关,水化学溶液对砂岩有一定的化学腐蚀作用,水化学溶液与冻融循环的耦合作用对岩石的损伤劣化是相互促进的,共同影响着砂岩的损伤劣化程度。

The damage degradation mechanism and physical and mechanical properties of sandstone under the coupling effect of chemical solution and freeze-thaw cycles are studied through laboratory tests. The sandstone specimens soaked in different chemical solutions are studied by freeze-thaw cycle tests. The physical and mechanical properties of sandstone specimens due to different freeze-thaw cycles are measured at the same time. The results show that the damage deterioration mode of sandstone specimens is different under the coupling effect of chemical solution and freeze-thaw cycles. There are two main modes of sandstone deterioration, i.e., the grain spalling and scaling mode, and the fracturing mode. The damage degradation degree of the physical and mechanical characteristics of sandstone due to freeze-thaw cycles is the largest in strong acidic conditions（pH = 3.0）, and that in strong alkaline environment（pH=12.0）comes the second, that is, it has a certain degree of mitigation in the neutral to weakly alkaline environment, but the degradation still increases with the increase of cycling times continuously. The greater the concentration of Na_2SO_4 solution, the larger the reduction rate of freeze-thaw coefficient. The damage degradation degree of sandstone subjected to freeze-thaw cycles is the largest in 0.01 mol/L Na_2SO_4 pH=9.0 than that in 0.01 mol/L NaHCO_3 pH=9.0. The freeze-thaw damage of sandstone is closely related to water chemical environment. The chemical solutions have certain chemical etching effect on sandstone, and the coupling effect together with freeze-thaw cycles can give mutual effect on the degradation and damage of sandstone.