Abstract
In order to study the effect of water-rock interactions on shear strength characteristics, we performed shearing tests under varying hydrochemical environments. Moreover, a custom meso-shear test equipment for coal rock was used for the tests. Through 3D scanning of the shear fractures and scanning electron microscope imaging, we studied the effect of different pH chemical solutions on the shear strength and fracture characteristics of sandstones. We obtained three main results. With increasing solution acidity or alkalinity, water-hemical solution corrosivity increases. Moreover, the shear strength of sandstones reduces almost linearly and the fracture surfaces become smoother. The erosive effect is evidenced by the decrease in fracture surface fluctuations, roughness and the high-order microbulges, and scaling of the grain structure. A collection of characteristic parameters, including the maximum height Sh, the root mean square deviation Sq, the area ratio SA, and the slope root mean square S∆q, can be used to quantitatively describe the rough and irregular texture of the fracture surface.
Highlights
In order to study the effect of water-rock interactions on shear strength characteristics, we performed shearing tests under varying hydrochemical environments
Miao et al found the poisson’s ratio of granite increased after treatment with water and acidic solutions[16]. This is mainly due to the microstructural damage caused by chemical reactions between rock and chemical solution, which resulted in the macroscopic loosening and fragility of rocks
We used a PHS-2C acidimeter to measure the change of pH value of the chemical solutions during the whole soaking process
Summary
In order to study the effect of water-rock interactions on shear strength characteristics, we performed shearing tests under varying hydrochemical environments. A collection of characteristic parameters, including the maximum height Sh, the root mean square deviation Sq, the area ratio SA, and the slope root mean square S∆q, can be used to quantitatively describe the rough and irregular texture of the fracture surface During engineering activities such as the discharge of waste liquid in injection wells[1], geological sequestration of CO22,3, or large-scale hydrofracturing using acidic solutions[4], the rock mass is loaded and etched and corroded by the chemical solutions in the ambient environment. For sandstone, NaHCO3 and CaCl2 solutions produced the largest loss and smallest loss of strength, respectively These are mainly due to the chemical reaction between solutions and main mineral components of rock samples[21]
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