Roof structure of shallow coal seam group mining in Western China.

Jian Cao,Qingxiang Huang,Jianguo Wang

doi:10.1371/journal.pone.0255047

Jian Cao, Qingxiang Huang + Show 1 more

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https://doi.org/10.1371/journal.pone.0255047

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Abstract

In order to realize roof control of shallow coal seam group mining in Western China, combining with engineering statistics, physical simulation and theoretical analysis, the roof weighting characteristics during lower coal seam mining were revealed, and the classification of shallow coal seam group was proposed. Based on this, mechanical models of roof structure were set up, and the calculation method of support resistance was determined. The results show that the roof weighting is closely related to the interburden thickness and the mining height of lower coal seam, considering the ratio of interburden thickness to the mining height, as well as the key stratum structure, the classification of shallow coal seam group was put forward. The first type is shallow coal seam group with no key stratum (SCSG-No), its roof pressure is mainly affected by caving roof of upper coal seam, and the interburden roof forms slanting pillar-beam structure. The second type is shallow coal seam group with single key stratum (SCSG-S), interburden roof represents step voussoir beam structure. The third type is shallow coal seam group with double key strata (SCSG-D), interburden roof can form double key strata structure, the lower key stratum forms slanting step voussoir beam structure, while the upper key stratum forms voussoir beam structure, besides, longwall face represents large—small periodic weighting. Through establishing the roof structure models, the calculation formulas of support resistance were determined, it can provide basis for roof control and promote safe mining in Western China.

Highlights

Shallow coal seams in Jurassic Coalfield are generally characterized by shallow depth, small interburden thickness, and 2–3 coal seams are mainly mined, it belongs to shallow coal seam group mining.Recently, the upper coal seam in Jurassic Coalfield was already mined out, and mainly mines lower coal seam
According to the engineering statistics and theoretical analysis above, based on the key strata in interburden and the index G, shallow coal seam group can be divided into three types below: (1) The first type is shallow coal seam group with no key stratum (SCSG-No)
M2 is the mining height of lower coal seam, m; Sh is the thickness of immediate roof, m; h is the thickness of key stratum, m; h1 is the thickness of load strata, m; L1 is the length of step voussoir beam block, m; R1 is the sliding pressure of block M, kN; R2 is the weight of load strata and block M, kN; q is the uniform distributed load, kN/m; θ1 is rotation angle of block M, ̊; ω1 is the subsidence of block M, m

Summary

Introduction

Shallow coal seams in Jurassic Coalfield are generally characterized by shallow depth (less than 300 m), small interburden (strata between upper and lower coal seam) thickness (less than 45 m), and 2–3 coal seams are mainly mined, it belongs to shallow coal seam group mining. As the lower coal seam mining, firstly, immediate roof fractures and caves, the single key stratum fractures periodically and forms step voussoir beam, the key stratum mainly bears the transmitting load of upper goaf (Fig 14). M2 is the mining height of lower coal seam, m; Sh is the thickness of immediate roof, m; h is the thickness of key stratum, m; h1 is the thickness of load strata, m; L1 is the length of step voussoir beam block, m; R1 is the sliding pressure of block M, kN; R2 is the weight of load strata and block M, kN; q is the uniform distributed load, kN/m; θ1 is rotation angle of block M, ̊; ω1 is the subsidence of block M, m. Based on formulas (20)-(26), the rational support resistance of large periodic weighting is:

À 0:5h cot a þ 0:25L1 h À m2 þ 0:3Sh ðhrg þ h1r1gÞbL1 þ

Findings

Conclusions