Similar experimental study on retaining waterproof coal pillar in composite strata mining

Y Q Wang,W J Zhu,Z P Wang,X Wang,B S Yang,J S Zhang

doi:10.1038/s41598-022-05369-7

Abstract

Numerous field examples of coal seam mining show that when coal seams under confined water are mined close to faults, water inrush effects on complex mining surfaces occur. Obeying similarity rules, physical similarity models consisting of sand, lime, and plaster were used to investigate the water conducting process, along with stress and displacement measured by a combination of mechanical senor, total station, and video camera-. Comparing the physical model tests with the calculation results of elastoplastic limit equilibrium theory, the rationality of the model has been verified. Besides, a safe width of the waterproof coal pillar has been obtained. It can be demonstrated from the model observations that the coal seam in front of the mining can be divided into three areas with different characteristics of stress and displacement, namely, which are the fault-affected area, the elastic area, and the plastic yield crack area. A closed-loop water inlet and outlet pipeline composed of a water control platform that can provide stable water pressure, and water bags pre-buried in the fault was used to simulate the water conduction in the fracture zone. Integrate the development law of stress, displacement, and water conduction coming from the upper and lower walls of the fault to further determine the reasonable width of the waterproof coal pillar.

Highlights

Numerous field examples of coal seam mining show that when coal seams under confined water are mined close to faults, water inrush effects on complex mining surfaces occur
Field examples show that when mining under aquifer, three areas with different mechanical properties can occur in the upper goaf; the caved zone, fracture zone, and the continuous deformation z one[6,7]
The observation clearly demonstrates that, the water guiding height will greatly increase the possibility of water inrush in the coal seam face for the water guiding water bag 4 located on the top of the coal seam, which assumed that it is the critical condition of water inrush at this time, in order to ensure the safe mining of the coal seam, a conservative waterproof coal pillar width can be obtained

Summary

Limestone

The aggregate is ordinary river sand, with a diameter less than 1.5 mm, and the binder is composed of lime, gypsum, and mica powder simulating the rock bedding structure. The material and water were mixed and stirred evenly to prepare a cylindrical specimen, with the influence of various materials on the compressive strength was obtained from uniaxial compression test (Fig. 7). After completing a series of uniaxial compression tests, the similarity strength parameter of the model is taken as Eq (2). The mixture and model parameters of the prototype rock mass are shown in Table.[3]. Where Cσ is the constant of strength; σρ, σm are the compressive strength of prototype and model respectively. This experiment adopts the two-dimensional similar material simulation experiment platform of the geotechnical laboratory of Anhui Jianzhu University, which size is 3.0 m (length) × 0.4 m (width) × 1.7 m (height).

F22 Fine sandtone

Findings

Discussion

Conclusions