Abstract
Longitudinal connected fissures in a shallowly buried coal face with thin bedrock are the main factor causing sand-burst accidents, water-burst accidents, and abnormal increases in water inflow. To understand the evolution of longitudinal connected fissures and propose method for controlling such fissures, 3-1 Coal of the Jinjie Coal Mine in Shendong Coal Group, China, was used as a case study. Physical simulation, numerical simulation, field measurements, and other measures were carried out to analyze thoroughly the opening and closure of fissures. At the same time, the stage characteristics of fissures evolution process are also obtained. The results indicate that when periodic weighting occurs, a longitudinal connected fissure starts to open. As the coal face moves on, the fissure expands gradually with the dynamic changes in horizontal force and rock dislocation; when the expansion reaches its limit, the key rock falls and the longitudinal connected fissure rapidly closes. With the advent of the next periodic weighting, the longitudinal connected fissure compacts further and the next longitudinal connected fissure appears. The formation of longitudinal connected fissures is described with reference to three factors: the advancement speed of the coal face, the holding power of the hydraulic support, and the filling degree of the goaf area, all of which can be easily controlled by engineering means. This study provides a basis for control of sand-burst accidents, water-burst accidents, and abnormal increase in water inflow in a shallow coal face with thin bedrock.
Highlights
Physical Simulation of the Evolution of Longitudinal Connected FissuresE aquifer in the unconsolidated layers was modeled in the physical simulation by gravel and fine sand of grain size 0.5–1.0 cm (Figure 4)
We deduce that the formation of longitudinal connected fissures through the overburden rock fractured during the mining process was the intrinsic cause of the abnormal water flow. erefore, adjusting the mining parameters to control the evolution of longitudinal connected fissures will be an effective way to control abnormal water flow in the coal face
When the coal face had advanced to 100 m, the first periodic weighting started to occur (Figures 5(a) and 6(a)) and a longitudinal connected fissure approximately 0.22 m long appeared between the coal face and the unconsolidated layers
Summary
E aquifer in the unconsolidated layers was modeled in the physical simulation by gravel and fine sand of grain size 0.5–1.0 cm (Figure 4). E periodic weighting length was about 25 m for the formation of longitudinal connected fissures in the coal face. E sizes of the unconsolidated fissure in the bedrock through time are shown (Figure 6) and were referenced in the model for the physical simulation. When the coal face had advanced to 100 m, the first periodic weighting started to occur (Figures 5(a) and 6(a)) and a longitudinal connected fissure approximately 0.22 m long appeared between the coal face and the unconsolidated layers. When the coal face had advanced to 120 m, the bedrock blocks turned to the limit (Figures 5(b) and 6(b)) and the longitudinal connected fissure reached its maximum length of about 1.53 m. Table 1: ickness and physical-mechanical properties of analog strata
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