Physical and Mechanical Properties Evolution of Coal Subjected to Salty Solution and a Damage Constitutive Model under Uniaxial Compression

Abstract

Many underground reservoirs for storing water have been constructed in China’s western coal mines to protect water resources. Coal pillars which work as dams are subjected to a long-term soaking environment of concentrated salty water. Deterioration of the coal dam under the attack of the salty solution poses challenges for the long-term stability and serviceability of underground reservoirs. The evolution of the physical and mechanical properties of coal subjected to salty solutions are investigated in this paper. Coal from a western China mine is made to standard cylinder samples. The salty solution is prepared according to chemical tests of water in the mine. The coal samples soaked in the salty solution for different periods are tested by scanning electron microscope, nuclear magnetic resonance, and ultrasonic detector techniques. Further, uniaxial compression tests are carried out on the coal specimens. The evolutions of porosity, mass, microstructures of coal, solution pH values, and stress–strain curves are obtained for different soaking times. Moreover, a damage constitutive model for the coal samples is developed by introducing a chemical-stress coupling damage variable. The result shows that the corrosion effect of salty solution on coal samples becomes stronger with increasing immersion time. The degree of deterioration of the longitudinal wave velocity (vp) is positively correlated with the immersion time. With the increase in soaking times, the porosity of coal gradually increases. The relative mass firstly displays an increasing trend and then decreases with time. The peak strength and elastic modulus of coal decreases exponentially with soaking times. The developed damage constitutive model can well describe the stress–strain behavior of coal subjected to salty solution under the uniaxial compression.

Sulfate diffusion in coal pillar: experimental data and prediction model

“…The sulfate concentration in mine water varies from mining regions, mines and working faces, e.g., 0.05-0.18 mol/L in Shendong mining region (Zhou and Wang 2017), 0.12 mol/L in Lingxin coal mine (Wang et al 2021a, b) and 0.17 mol/L in Ningdong mining region (Jiang et al 2020). Thus, the sulfate concentrations in mine water are set as 0.01, 0.05, 0.10 and 0.20 mol/L for discussions.…”

“…To predict the service life of coal dam induced by sulfate attacking, a preliminary method is proposed. The basic assumptions are given as follows: (1) With reference to previous mechanical tests on coal soaking in sulfate solution (Wang et al 2021a, b), the critical sulfate concentration in coal is assumed as 0.4% with which the strength of coal can be reduced by 50%. (2) For simplification, the coal dam will be out of service if half of the dam loses its 50% strength.…”

“…Coal dams or pillars are the main loadbearing structures for underground spaces after mining. Coal pillars are normally considered as short-term structures for conventional mining (Wang et al 2021a, b). However, the utilization of underground spaces after coal mining for water and heat storage poses a huge challenge for the long-term stability of coal pillars or dams, especially bearing in mind water-coal interaction (Bian et al 2021;Liu et al2021;Liu et al 2022a, b;Liu et al2022a, b).…”

“…Li et al (2020) discussed the mechanical properties and failure characteristics of coal rock with different combinations of acid solutions and found and hydrofluoric acid can effectively dissolve minerals containing kaolinite and calcite. Wang et al (2021a, b) carried out experiments on coal deterioration induced by sulfate attacking and found the strength can be reduced by 50% for coal with 0.4% of sulfate ion. Therefore, chemical ions in mine water have significant effects on the microstructures and mechanical properties of coal dam.…”

Analysis of mechanical response mechanism and energy evolution characteristics of saturated coal with a single pre-existing hole

“…On the one hand, the evolution law of cracks around holes is mainly studied from the perspective of damage mechanics [20][21][22][23] , On the other hand, the crack initiation, propagation and mechanical properties of rock mass with holes are analyzed from the point of view of fracture mechanics [24][25][26][27] , A series of signi cant research results have also been obtained on the mechanical properties of coal samples with water saturation, and the mechanical and acoustic emission characteristics of coal samples with different water content have been obtained [28][29][30][31][32][33] . There are still relatively few studies on the mechanical response mechanism, failure mode and energy evolution characteristics of saturated coal with a single pre-existing hole.…”