弱胶结砂岩水岩作用机制——以庆阳北石窟为例

选取庆阳北石窟赋存砂岩为研究对象,于室内分别设置冻融循环、干湿循环两组单因素风化模拟试验,经历30个周期,共计120d.结合岩样在宏观、局部、微观等不同维度下的劣化特征及表层矿物成分与元素的迁移规律对水岩作用机制全程跟踪评估.试验结果表明:在模拟试验前期,水-岩之间化学作用强烈,两组试验化学蚀变系数均发生陡增;随着试验继续,水-岩之间物理作用逐渐变强,冻融循环转为水体积膨胀对颗粒施加的拉、压应力作用,且率先在含水率最高处诱发裂隙.而干湿循环变为水对颗粒结构的机械冲刷,该过程则受水分运移及孔隙分布方式的共同支配;对于弱胶结砂岩,水-岩频繁作用导致的颗粒耦合关系改变是岩石劣化的关键.

Water-Rock Mechanism of Weakly Consolidated Sandstone: a Case Study of Qingyang North Grottoes

Qingyang north grottoes sandstone was selected as the research object, and two sets of single-factor weathering simulation experiments of freezing-thawing cycles and wetting-drying cycles for a total of 120d with 30 cycles were set up in laboratory. Combined with the deterioration characteristics of rock samples in different dimensions such as macro-scale, local scale, and micro-scale, as well as the migration patterns of surface mineral components and elements, the whole process of the water-rock interaction mechanism was tracked and evaluated. The experimental results showed that at the beginning of simulation experiments, the chemical interaction between water and rock was strong, and the chemical alteration coefficient of both groups increased sharply. With the cycles going on, the physical interaction between water and rock is getting stronger. The tensile and compressive stress are induced by the expansion of water volume between the particles during freezing-thawing cycles. The fracture was first induced at the part with highest moisture content. The granular structure is mechanically eroded by the flow of water during wetting-drying cycles, and the process is mutually controlled by moisture migration and pore distribution. For weakly consolidated sandstone, the key to sandstone deterioration is the change of particle coupling relation caused by frequent water-rock interaction.