砂岩冻融损伤机制的理论分析和试验验证

 由于岩石性质的复杂性和环境条件的多变性，岩石冻融损伤并不是单一机制造成的，应是各种机制共同作用的结果，但往往存在主导性的机制。首先对已有冻融损伤理论进行系统介绍，分析各自的适用条件。之后探讨多孔岩石(以砂岩为例)的孔隙结构对冻融损伤机制的控制性作用，并定义“特征冻融损伤单元”。利用热力学原理分析不同的冻结条件下砂岩内部可能发生的冻融损伤机制和主导机制。当冻结速率低时，毛细管机制(理论)和结晶压机制(理论)应在岩石的冻融损伤中起主导作用，而体积膨胀机制则受到抑制；当冻结速率高时，体积膨胀机制和静水压机制应在岩石的冻融损伤中起主导作用，而毛细管机制和结晶压机制则受到抑制。最后利用砂岩的冻融损伤试验--包括利用环境扫描电镜(ESEM)对砂岩孔隙结构及冻融损伤的微观观察和利用应变片对砂岩的冻胀变形过程的监测，对砂岩的冻融损伤机制进行了验证，试验结果与理论分析的结论相一致。

Theoretical analysis and experimental verifications of frost damage mechanism of sandstone

Due to the complexity of rock properties and the variability of environmental conditions，frost damage of rock can hardly be attributed to one single mechanism. Nonetheless，in most of the cases，one or more mechanisms dominate the process. We firstly reviewed the existing theories on frost damage and compare their applicable conditions. Afterwards the controlling role of the pore structure of sandstone(as an example of porous rock) in the frost damage process was discussed，and the “representative element of frost damage” was defined. The probable damage mechanisms and the predominant mechanism of sandstone under different freezing patterns were identified according to the thermodynamics. Under the low freezing rate，the capillary and crystallization pressure were found to play a key role in damaging sandstone，while the volumetric expansion process was restrained. While under the high freezing rate，the volumetric expansion process and hydraulic pressure process contributed predominately to the damage of sandstone rather than the capillary and crystallization pressure. To test the above findings，a series of experiments on frost damage of sandstone were conducted，including the direct observation of the microstructure of sandstone under environmental scanning electron microscope(ESEM) and monitoring of the frost deformation of sandstone using strain gages. The experimental results are consistent with the theoretical analysis.