Elsevier

Safety Science

Volume 114, April 2019, Pages 1-11
Safety Science

Theoretical and numerical investigations of floor dynamic rupture: A case study in Zhaolou Coal Mine, China

https://doi.org/10.1016/j.ssci.2018.12.016Get rights and content

Highlights

  • A cusp catastrophe model is proposed to investigate the mechanism of the floor dynamic rupture and its influence factors.

  • A fish function incorporated in UDEC is put forward to calculate the released kinetic energy influenced by the factors.

  • Seismic computed tomography is utilized to analyse the evolution of stress distribution.

Abstract

The floor dynamic rupture occurred in the 1306 longwall coal face (LCF) in Zhaolou Coal Mine was induced due to the superposition of static and dynamic stresses. In order to investigate the triggering conditions of the floor buckling, this study established a cusp catastrophe model based on elastic thin plate theory. During the occurrence of floor dynamic rupture process, the released energy was calculated, using elasticity modulus (E), Poisson ratio (μ), thickness (h), roadway width (a), maximum cohesion (σ0) and horizontal stress (σh) as influencing factors. Furthermore, by utilizing discrete element method (UDEC), and applying an artificial source in the model, a fish function was developed to harness the released kinetic energy (Ek) and its vibration curves. The results indicated that the main control factors of the floor dynamic rupture were the roadway width and horizontal stress, both of which had a positive correlation with the floor dynamic rupture risk. According to seismic computed tomography, the high horizontal stress in the 1306 LCF was verified through the evolution of P-wave velocity. The above mentioned findings, coupled with the catastrophe theory, UDEC and seismic computed tomography, could propose a certain reference for the pre-warning and prevention of the floor dynamic rupture.

Introduction

Highly word-wide demand on fossil fuel especially on the coal has caused a tremendous increase in the depth of mining operations at an annual rate of 10–20 m (Dou and He, 2001). The floor dynamic rupture is a violent form of floor heave, which is the main component of roadway deformation failure (Chang et al., 2013). Recently, several scholars have studied the roadway failure and stability using numerical simulation, laboratory experiments, and in-situ tests. Jiang et al. (Jiang et al., 2004) adopted the theoretical analysis and the similarity simulation test to research the mechanism of the floor heave. Since 2001, researchers have been using numerical simulation to study the mechanism and the control method of floor heave (Li and Liu, 2013, Lin et al., 2013, Zhao et al., 2015, Xu et al., 2016). Jeon et al. (Jeon et al., 2004)studied the excavation related problems through utilizing small–scale model tests. Lee and Schubert (Lee and Schubert, 2008) conducted small scale model tests to investigate the failure mechanism of tunnel faces. Zhu et al. (Zhu et al., 2011) employed a Quasi-three-dimensional physical model test to study the failure mechanism of the caverns under high in-situ stresses. Zhong et al. (Zhong et al., 2012) analysed the occurrence mechanism of floor heave for soft-rock tunnels on the basis of field investigations and geological surveys. Evidently, the floor heave mentioned aboveis a process phenomenon with time effect, ranging from hours to days and even months. However, its occurrence within short period of time e.g. a few seconds and the instant energy release could cause the floor dynamic rupture.

In deep mining operations, the high stress concentration could induce violent coal-rock failures and associated strong seismicities. In other words, a dynamic rupture might well occur when the total stress (the superposition of the static stress in the coal and the dynamic stress induced by tremors) exceeds the critical stress or the strength of the coal (Li et al., 2014). Unfortunately, the dynamic rupture events have posed severe threats to mine workers and also impeded the continuous production in coal mines (Dou and He, 2001). In recent years, many scholars have investigated the dynamic rupture induced by hard roof (He et al., 2016, Lu et al., 2015), coal pillar (Cao et al., 2016, Fakhimi et al., 2016), fault slip (Zhu et al., 2015, Li et al., 2016), tectonic stress (Shabarov, 2001, Chen et al., 2011), based on the frequently-used parameters, such as stress, strain and energy. The methods normally employed are theoretical analysis (Li et al., 2014, Li et al., 2010), numerical simulation (Zhu et al., 2015), similarity simulation test (Cai et al., 2018) and seismic computed tomography (Cai et al., 2014).

However, few literatures have focused on the catastrophe model, even though dynamic rupture of coal-rock mass is a catastrophe process in equilibrium state. The sudden failure of coal-rock mass depicts a nonlinear mechanical behaviour. Based on the plastic strain catastrophe theory, numerical results and in-situ data, Li et al. (Li et al., 2011) analysed and obtained the limit displacements for the stability of surrounding rock, corresponding to the in-situ monitoring technology. Kong et al. (Kong and Hu, 2013) introduced the basic principle of catastrophe theory, which focuses on a cusp catastrophic model to build a simplified mechanical model for the surrounding rock, and finally obtained the instability of surrounding. Yu et al. (Yu and Liu, 2015) introduced the cusp displacement catastrophe theory to propose a new method about instability failure of the interbed for gas storage cavern in bedded salt in solution mining. According to the surrounding rock instability, Zuo et al. (Zuo et al., 2015) built the total potential energy function of fault surrounding rock system in the application of tunnel across the fault to establish the standard type of catastrophe model and the bifurcation set equation.

In this paper, the mechanism of floor dynamic rupture was investigated based on the catastrophe theory. Susequently, the process of the floor dynamic rupture was reproduced by UDEC according to the geological conditions of the 1306 LCF in Zhaolou Coal Mine. Meanwhile, the vibration curves of the released kinetic energy influenced by the factors were further explored. The method of seismic computed tomography was used to find the evolution of stress distribution.

Section snippets

Production and geological conditions of coal face

The 1306 LCF with full-mechanized caving mining process is located in the first mining area at the Zhaolou Coal Mine, in Shandong, China. The main roadways are in the East, the north is the 1304 LCF (mined) and 1305 LCF (unmined), and the south is the 1307 LCF (unmined). The effective strike length of the panel is 1109 m, the incline length is 196 m and the maximum burying depth is 1013 m. The mining seam is 3# coal seam with thickness of 1.41–8.62 m (the average is 5.75 m) and average dip

Mechanism of the floor dynamic rupture

The floor dynamic rupture occurred due to the superposition of static and dynamic stresses which belonged to the external cause. Several scholars have put forward the methods to research the internal cause. It was revealed that a composite floor would be formed, due to soft rock, coal seam or weak interlayer. With the accumulation of elastic energy and resultant high horizontal stress, the floor would buckle and lead to the occurrence of dynamic rupture while a large volume of elastic energy is

Numerical simulation of the dynamic rupture failure in floor

The released energy in floor has been calculated in the static stress condition which could be inaccurate due to the complicated geological conditions and dynamic stress in coal mine. The dynamic stress plays a vital role in the floor dynamic rupture. Therefore, in order to obtain the main control factors of the above six factors, UDEC is employed to carry out the numerical simulation of the dynamic rupture failure in floor. According to the geological condition of the 1306 LCF in Zhaolou Coal

Verification of high static stress data: A seismic computed tomography approach

The stress field in coal and rock mass in coal mines could be approximately obtained using theoretical calculation and numerical simulation. However, due to complex geological conditions and mining activities, it is very difficult to obtain the true in-situ stress field in time and space. To solve this problem, several researchers have carried out the research on P-wave tomography for evaluating the stress concentration level of coal and rock in coal mines (Lu et al., 2015, Cai et al., 2014,

Conclusions

The floor dynamic rupture that occurred in the 1306 LCF in Zhaolou Coal Mine was induced by the superposition of static and dynamic stresses, which severely impeded the safety production. In order to explore the main control factors of the floor dynamic rupture, the methodologies of catastrophe theory, UDEC and seismic computed tomography were utilized. The main conclusions are as follows:

The cusp catastrophe model was established to acquire the mechanical condition of floor buckling and

Acknowledgments

The authors gratefully acknowledge financial support for this work provided by the State Key Research Development Program of China (2016YFC0801408) and the Fundamental Research Funds for the Central Universities (2018ZDPY02).

References (37)

Cited by (0)

View full text