不同卸荷损伤程度砂岩吸水特性试验研究

针对边坡岩体开挖卸荷后遇水极易失稳的现象，以三峡库区典型砂岩为研究对象，通过三轴加卸荷试验确定岩样不同卸荷损伤程度，然后进行自由吸水试验，研究不同卸荷损伤程度砂岩的吸水特性变化规律。试验结果表明：① 岩样吸水后表面水位高度的变化具有明显的时间效应。吸水初期，水位高度增加速度较快，之后逐渐减小。② 岩样吸水稳定后，水位高度随卸荷量的增加而增加。当卸荷量较大，卸荷损伤岩样有裂缝产生时，吸水速度明显增加，且水位高度沿着裂缝均匀分布。③ 同一围压下的岩样，吸水率随着卸荷量的增加而增加，其增加速度也随着卸荷量的增加逐渐加快。这是由于随着卸荷量的增加，岩样内部裂纹逐渐扩展，当卸荷量继续增加至岩样内部裂纹贯通后，吸水率就随之急剧增加。当裂纹最终贯通以后，岩样的吸水率与围压之间的关系不再显著。④ 当卸荷量为一定值时，随着围压的增加，卸荷损伤岩样吸水率逐渐增加。但是当卸荷量较大时，岩样吸水率随着围压的增加先增大后减小，但变化幅度较小。上述成果可为开挖卸荷边坡支护时机及方案的选择提供一定的借鉴。

Experimental research on absorption characteristic of sandstone under different unloading damaged degree

In the view of the phenomenon that the slope is vulnerable to lossing stability after excavation unloading, we take typical sandstone in the Three Gorges Reservoir area as the research object. The rock samples unloading-damaged in different degrees are determined by triaxial loading and unloading test, and then the free water absorption test was carried out. The variation of water absorption characteristics of sandstone unloading-damaged in different degrees were studied. The results showed that:(1) the changes of water levels in rock samples had an obvious time effect. In the early stage of water absorption, the water level increased rapidly and then gradually decreased. (2) after the water absorption tended to be stable, the water levels in samples increased with the increase of unloading degree. When the unloading degree was large, which resulted in the fracture of rock samples, the water absorption rate increased obviously, and the water level height distributed evenly along the fracture. (3) under the same confining pressure, the water absorption rate increased with the increase of unloading degree, and the increasing speed went upward with the unloading degree. The reason was that the internal cracks of rock samples gradually expanded with the unloading degree, and when the increasing unloading made the internal cracks penetrated, the water absorption rate increased sharply, and in this case the relationship between water absorption and confining pressure was no longer significant. (4)The water absorption rate of rock sample increased with the confining pressure when the unloading degree was a certain value. However, in severe unloading conditions, with the increase of confining pressure, the water absorption rate increased first and then decreased, but the variation was small. The results can be used for reference in the selection of supporting timing and scheme for excavation unloading slope.