Water Inrush from Pregrouting Fractures Induced by Mining Activities and Its Engineering Control Method Optimization

Jianbo Li

doi:10.1155/2019/6243609

Abstract

Water inrush accidents during coal mining still occur after reinforcement of fissured water bearing strata underlying coal seams through grouting, which seriously troubles field technicians. In order to further prevent the water inrush, especially the water inrush after grouting reinforcement, the grouting technique needs to be improved. Experimental design, theoretical analysis, and numerical simulation have been carried out in sequence. On the microscale level, the relationship between strains and water flow rate was analyzed through laboratory experiments; on the macroscale level, the propagation mechanism of grouting cracks resulting from the rock strata deformation during coal production was analyzed with rock beam theory, and then a new model of casing pipes preventing water inrush by controlling deformation of the floor rock strata is proposed. The laboratory test results show that the response of the radial strain and the water flow rate to mining operation is consistent and positively correlated and verify that it is feasible to reduce water inrush disaster by controlling deformation of the rock strata. The deformation governing equation of the casing pipes is deduced theoretically. At last, the numerical calculation was done to prove the effectiveness of controlling the floor rock strata deformation by the casing pipe group, which indicated that the displacement of the monitoring points after grouting is smaller than that before grouting practice. It is practicable to realize grouting technique optimization by the innovative adoption of the grouting casing pipes in the future.

Highlights

Introduction and BackgroundCoal is still of crucial significance for the economic development in domestic China
There are many factors affecting water inrush such as formation pressure, productivity, geologic structures, and the water pressure in the confined aquifer, though the declining of constraints due to mining is the major cause of the water-conducting failure of the floor rock strata in the coal seams [3]
On the microscale level, the laboratory experiment on the pregrouting fractures penetrated by confined water during mining activities was designed and completed, according to in situ stress conditions and rock samples drilled from coal seam floor rock strata. e results show that the response of the radial strain and the water flow rate to mining activities is consistent and positively correlated

Summary

Introduction and Background

Coal is still of crucial significance for the economic development in domestic China. There are three problems: (a) sealing and exerting high water pressure are very di cult; (b) it is di cult to determine similar materials due to the uncertainty of similarity ratio; (c) how to simulate mining operations after sealing In view of these reasons, this paper chooses a three-axial test machine (Figure 2). E test demonstrates that the grouting rock samples with vertical fractures through the rock pillar are easier to be penetrated by high pressure water when disturbed by mining activities rather than generating some new fractures. 3. Propagation of Grouting Cracks during Mining Operations in a Real Coal Mine ere are many research ideas to solve oor deformation and even failure, such as voussoir beam and key rock stratum [16]. When the internal stress σ is greater than the critical uniaxial strength of grouting cracks, the fracture is expanded and destroyed

Mechanism of Preventing Water Inrush by Grouting Casing Pipes

II III

Findings

Conclusions