Experimental Study on the Dilatancy of Rock Salt From an Unloading Path

Abstract

As underground storages produce gas, rock salt would always be in unloading paths. The dilatancy behavior of the surrounding rock salt has a great significance for the stability and tightness of the storages. This study investigated dilatancy properties of the rock salt from unloading paths where the confining pressure decreased progressively while the axial pressure was kept fixed. The results showed that: the initial confining pressure value has a rare influence on the dilatancy of the rock salt; an increasing axial pressure can promote the dilatancy of the rock salt; a slower unloading rate and higher temperature would accelerate the dilatancy rate and augment the total volumetric expansion. Compared with the results from conventional loading paths, the compression-dilatancy point is independent of the loading types and remain unchanged in cyclic loading tests. An empirical model to predict compression-dilatancy point was proposed. This model has a certain degree of the engineering significance for designing the operating gas pressure and predicting the dilatancy deformation of the surrounding rock, including porosity variation and permeability.

Mineralogy, microstructures and geomechanics of rock salt for underground gas storage

“…This brittle deformation occurs at very low effective confining pressure and high deviatoric stress (Cristescu & Hunsche, 1998; Urai et al, 2008), and leads to damage of the rock structure. Dilation is higher with a higher axial pressure, and faster dilation occurs for slower unloading and at higher temperature (Zhao et al, 2019). Dilatation or volume growth is of particular concern for the application of underground storage of gas or hazardous waste.…”