ISSN 1062-7391, Journal of Mining Science, 2017, Vol. 53, No. 5, pp. 811–817. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © V.E. Mirenkov, 2017, published in Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, 2017, No. 5, pp. 15–22.
_________________________________ GEOMECHANICS _______________________________
Interaction between Enclosing Rocks and Roof Support
V. E. Mirenkov
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences,
Novosibirsk, 630091 Russia
Received May 26, 2017
Abstract—The author proposes a new analytical approach to the description of static, kinematic and
dynamic aspects of interaction between mine roof support and host rock mass in the course of coal
extraction. Inclusion of the static component suggests the classical construction of a probable fracture line.
The kinematic aspect means accounting for the influence of the overlying rock mass weight on the process
of failure. The dynamics of failure during expansion of mined-out area is illustrated in terms of a unit event
of production heading advance. Considered jointly, the three components of the damage accumulation
process in rock mass allow more accurate control over destructive manifestation of rock pressure.
Keywords: Underground opening, longwall mining, stresses, displacements, damage accumulation, fracture,
overlying rock weight, support, interaction process.
Ground control is an essential issue in underground coal mining. Many problems are associated
with the rock pressure increase at deeper levels in mines. The most important problems include
increasing accident rate in longwall faces and sidewall instability; greater costs of roof support
advance in entries exposed to compression; dynamic events, coal and gas outbursts, mine bumps, clay
inrush, etc. Hard roofs pose particular problems in mining which are not always well resolved in
practices, though being quite a typical case.
Coal extraction commonly advances in two directions: along and across the longwall face.
Regulations for hard roof collapse imply fluid injection into the roof at certain spans of the mined-out
area (goaf) [1, 2]. In these conditions, movable roof supports advance unit by unit.
According to the classical approach to failure modeling, dynamic effects of overburden pressure in
longwall face are predicted based on viscoelastic or rheological solutions to the respective problem
. However, the failure point predicted with such solutions differs notably from the real case and
requires various corrections. For instance, the respective prediction in  consists in estimating the
point of yield (instability) in rocks subject to accelerating creep around several neighbor support
units. In this case, analysis applies to roof-floor convergence during a working cycle.
Assume that stress and strain have been calculated and the respective limit surface of possible
failure has been divided according to the selected strength theory. The coal face is assumed to
advance until stress on these surfaces exceeds the allowable limit. This is a static approach to failure
Coal face advance along the longwall and the related movements of support units produce a bench.
Figure 1 shows the surface of roof displacement increment at an elementary step of coal face advance
l toward the х axis accompanied by an impact of the roof against the next support unit . The coal
face displacement L toward the у axis leads to increase in displacement during the following
movements of the support units, and hence to further increase in load upon the units. This is the
dynamic aspect of the mining process.