Deterioration mechanism and dynamic constitutive model of coal-rock assemblages considering chemical corrosion and impact damage

Abstract

To reveal the deterioration mechanism of coal-rock assemblages under chemical corrosion and dynamic loading, chemical corrosion and dynamic impact experiments were conducted. Under different chemical corrosion conditions, the weakening characteristics, observable characteristics, softening characteristics of the dynamic parameters, dynamic failure characteristics, dynamic failure forms and dynamic microscopic characteristics were analyzed. Under each corrosion condition, the dynamic elastic modulus, dynamic deformation modulus and dynamic peak intensity tended to decrease with immersing time. The dynamic elastic modulus, dynamic deformation modulus and dynamic peak intensity exhibited an inverted U-shaped trend. Under dynamic impact, the failure process of acidly corroded samples can be divided into the following stages: the initial stage, elastic energy accumulation stage, local failure of coal and secondary rock crack expansion stage, coal fragment ejection stage, rock spalling stage and complete instability stage. Under dynamic impact, failure modes exist: coal crushing failure, rock fragmenting failure, rock splitting failure and full splitting failure. After impact failure, sample fragments are distributed in powder, granular, cone and block forms. Based on Zhu-Wang-Tang nonlinear viscoelastic properties, a model considering chemical corrosion and impact damage was proposed. The combined effects of chemical and impact-induced damage on the dynamic mechanical properties of coal-rock assemblages were systematically analyzed.

1. Introduction

Coal and rock are natural minerals. The mechanical properties and failure mechanism of these materials are closely related to the chemical corrosion environment [1]. With infrastructure development, geotechnical engineering, tunneling engineering, water conservancy engineering and deep mining engineering are experiencing the impact of acid-alkaline environment corrosion caused by complex hydrological conditions [2]. Water contains complex chemical ions with different pH. It is important in determining the deformation and failure process of coal and rock. Moreover, the pH of water is affected by various factors. The pH can be different in different regions [3]. Changes in pH intensify water–rock deterioration. This can lead to a significant decrease in rock strength [4]. Owing to the coupling of chemistry and mechanics, water-rock interactions greatly affect the structural stability of strata [5,6]. The interaction between chemical solutions and rock can cause geotechnical disasters such as landslides, dam foundation deformation, tunnel instability and collapse [7–9].

To study the effects of chemical solutions on the mechanical properties of coal and rock, various experiments have been conducted, and remarkable results have been achieved. A previous study revealed that chemical solution interactions with coal and rock cause internal structure deterioration, weakening the load-bearing performance of coal and rock [10,11]. Huang et al. [12] reported that the deterioration effect of chemical solutions on rocks is due mainly to their ability to promote particle spalling and surface crack formation. Mei et al. [13] conducted electron microscope scanning experiments on rocks immersed in hydrochloric acid solution. Rocks treated with hydrochloric acid showed significant surface alterations, indicating the corrosive impact of acidic environments.