Abstract
Large deformation and failure of soft rock are pressing problems in the mining practice. This paper provides a case study on failure mechanisms and support approaches for a water-rich soft rock roadway in tectonic stress areas of the Wangzhuang coal mine, China. Mechanic properties of rock mass related to the roadway are calibrated via a geological strength index method (GSI), based on which a corresponding numerical simulation model is established in the Universal Discrete Element Code (UDEC) software. The failure mechanism of the roadway under water-saturating and weathering conditions is revealed by field tests and numerical simulation. It is found that the stress evolution and crack development are affected by weathering and horizontal tectonic stresses. The roadway roof and floor suffer from high stress concentration and continuous cracking, and are consequently seen with rock failure, strength weakening, and pressure relief. Unfortunately, the current support system fails to restrain rock weathering and strength weakening, and the roadway is found with serious floor heave, roof subsidence, and large asymmetric deformation. Accordingly, a new combined support system of “bolt–cable–mesh–shotcrete + grouting” is proposed. Moreover, numerical simulation and field testing are conducted to validate the feasibility and effectiveness of the proposed approach, the results of which demonstrate the capacity of the proposed new support method to perfectly control the surrounding rock. Findings of this research can provide valuable references for support engineering in the soft rock roadway under analogous geological conditions.
Highlights
In 2018, China’s coal production reached 3.68 billion tons, growing by 4.5% every year [1]
Tremendous coal production pressures force many coal mines to shift into deep-buried coal seams and those with inferior occurrence conditions
It is verified that water can considerably reduce uniaxial compression strengths of sandstone specimens [8]; swelling pressures inside rock mass containing swelling components, e.g., montmorillonite and kaolinite, due to water soaking, can promote instability risks of roadway surrounding rocks [9]
Summary
In 2018, China’s coal production reached 3.68 billion tons, growing by 4.5% every year [1]. The applied pre-stress can enhance the mechanical properties of bolted rock, such as Young’s modulus and cohesion In this context, a stable load-bearing structure coupling support materials and intrinsic rock mass self-stabilizing strength can be greatly helpful. Numerous types of combined support systems were adopted to solve large deformation problems of soft rock roadways and were proven to be effective, such as yielding bolt–grouting support [29], combined support with U-shaped steel sets and anchor–grouting [23], support system with square steel confined concrete [30], and combined support with concrete shell and “bolt–cable–mesh–shotcrete” [2] They were well performed, the aforementioned surrounding rock control methods of soft rock roadways are not completely applicable to other support engineering projects with special geological setting, e.g., roadways with high water content in the surrounding rock, which are repeatedly repaired. Findings of this paper are expected to provide valuable references for support practices under analogous geological conditions
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