Numerical Investigation on the Ground Response of a Gob-Side Entry in an Extra-Thick Coal Seam

H. Zuo,Giuseppe Ruta,H.M. Zhu,Y. Li,G.C. Zhang,G.Z. Tao,C.W. Zang

doi:10.1155/2021/8838505

H. Zuo, Giuseppe Ruta + Show 5 more

Open Access

https://doi.org/10.1155/2021/8838505

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Abstract

This study was aimed at the large deformation phenomenon of rock mass surrounding the gob-side entry driven in a 20 m extra-thick coal seam. Taking tailgate 8211 as the engineering background, a numerical investigation was employed to analyze the deformation law of the gob-side entry. The study results are as follows. (1) Because the immediate roof was composed of weak coal mass with a thickness of 17 m, the roof coal mass was vulnerable to fail with the effect of overlying strata pressure; thus, a visual subsidence of roof coal mass with a maximum convergence of 800 mm was observed in the field. (2) The bearing capacity of the coal pillar was significantly less than that of the panel rib, resulting in the pillar failing more easily under the ground pressure and then generating large-scale squeezing deformation. (3) The roof and panel rib were in a state of shear failure with a failure depth of about 5 m. The coal pillar was entirely in a state of plastic failure. (4) A support scheme including an asymmetric anchor beam truss, roof angle anchor cable, and anchor cable combination structure was proposed. The field work confirmed that this support scheme could efficiently control the deformation and failure of the rock mass surrounding the gob-side entry. This study provides the theoretical basis and technical support for the control of rocks surrounding the gob-side entry in similar conditions.

Highlights

E immediate roof was a coarse sandstone with an average thickness of 7.3 m, having a gray-white, coarse-grained, and massive structure. e main roof was a fine sandstone, with an average thickness of 14.7 m, having a gray-white, medium-to fine-grained, and massive structure. e immediate floor was mudstone, with an average thickness of 5 m
It is well known that coal and rock mass may have plenty of discontinuous, which affect the stability of underground structures more or less, depending on the mechanical behavior of the discontinuities
Continuum-based methods are incapable of modelling discontinuities, rock mass properties estimated from the intact cores properties using the Hoek–Brown criterion can be performed in the model, which are effective properties that accounted for the rock discontinuities. erefore, FLAC3D simulation software was used to analyze the distribution characteristics of the displacement, stress, and failure fields during gob-side entry driven with a narrow coal pillar [20, 21]

Summary

MPa 9m

–7.0000E + 06 –9.0000E + –1.1000E + –1.3000E + 07 –1.5000E + 07 –1.7000E + 07 –1.9000E + 07 –2.1000E + 07. For the coal pillar rib, a maximum stress of 8 MPa occurred, which was greater than the original rock stress by 7.5 MPa. (3) Based on the distribution trend of the stress and plastic zone of the two ribs, it can be concluded that, the coal pillar was totally in a state of shear failure, the stress of the coal body exceeded the original stress within 1.5 m of the central part of the coal pillar. Is indicates that the coal pillar still had a certain degree of bearing capacity, which could meet the current demand for the ground control. It was still necessary to control the plastic damage range of the shallow coal body to avoid excessive horizontal displacement of the coal pillar

Ground Control of Surrounding Rock of the Gob-Side Entry

Engineering Application

Conclusion