Investigation of capillary water migration in the sandstone block based on electrical resistivity measurements

Abstract

Capillary water migration observed in sandstone block seriously affects pore structure and mechanical properties under the influence of the natural environment. In addition to continuous capillary action, the salt solution will be crystallized in the pores under the dry-wet cycles, and thereby deterioration occurs on the surface. To investigate the spatial and temporal evolution of material structure, a series of capillary water absorption tests were carried out on sandstone samples. Furthermore, stereo microscope and high-density resistivity instrument were conducted to monitor the characteristics of the surface and internal pores at intervals. Meanwhile, a novel Terzaghi model was proposed for modeling the variation trend of capillary water rise over time, in which the variation in porosity were characterized by saturated degree. The electrical resistivity measurements in millimeter-scale show that the rising trend of the dry-wet interface resembles the saddle shape. Moreover, the soluble salt is more enriched near the dry-wet interface under the capillary action due to the slow rise of the salt solution when it reaches the dry-wet interface. With the increase of dry-wet cycles, an obvious salt layer appeared on the surface accompanied by sandstone block crisp and pulverized phenomena, and significantly increased the capillary water absorption rate and porosity. In detail, the maximum mass loss due to mineral detachment of the surface reaches 2% in a single dry-wet cycle. Additionally, the study provides some references for evaluating the capillary action and deterioration mechanism of similar porous media materials by using a rapid and nondestructive method.