Deformation mechanisms in a coal mine roadway in extremely swelling soft rock

Abstract

The problem of roadway support in swelling soft rock was one of the challenging problems during mining. For most geological conditions, combinations of two or more supporting approaches could meet the requirements of most roadways; however, in extremely swelling soft rock, combined approaches even could not control large deformations. The purpose of this work was to probe the roadway deformation mechanisms in extremely swelling soft rock. Based on the main return air-way in a coal mine, deformation monitoring and geomechanical analysis were conducted, as well as plastic zone mechanical model was analysed. Results indicated that this soft rock was potentially very swelling. When the ground stress acted alone, the support strength needed in situ was not too large and combined supporting approaches could meet this requirement; however, when this potential released, the roadway would undergo permanent deformation. When the loose zone reached 3 m within surrounding rock, remote stress p∞ and supporting stress P presented a linear relationship. Namely, the greater the swelling stress, the more difficult it would be in roadway supporting. So in this extremely swelling soft rock, a better way to control roadway deformation was to control the releasing of surrounding rock’s swelling potential.

Assessment of Bearing Capacity and Stiffness in New Steel Sets Used for Roadway Support in Coal Mines

“…According to the swelling soft rock rating system proposed by Sun Xiaoming [30], mudstones in Chagannuoer belong to extremely swelling soft rocks. Roadway deformation results in Chagannuoer coal field are shown in Figure 1 [28]. Roadway deforms largely and continuously.…”

“…Chagannuoer coal field is a typical swelling soft rock field in Inner Mongolia of China. In the field, roof and floor of coal seam are primarily mudstone with extremely low strength [28,29]. Laboratory tests showed that the mudstone is primarily composed of clay minerals (60.6% in content).…”

“…Laboratory tests showed that the mudstone is primarily composed of clay minerals (60.6% in content). Worse still was that the clay minerals were primarily highly swelling montmorillonites, illites, and kaolinite [28]. According to the swelling soft rock rating system proposed by Sun Xiaoming [30], mudstones in Chagannuoer belong to extremely swelling soft rocks.…”

“…Roadway deforms largely and continuously. Several support approaches [28] have been tested in situ, but almost all failed and the roadway needs to be repaired all the time to maintain normal use. split or dilation of rods) or by cement grouting, which had low strength and were only suitable for some simple geological conditions.…”

“…Roadway deforms largely and continuously. Several support approaches [28] have been tested in situ, but almost all failed and the roadway needs to be repaired all the time to maintain normal use. In swelling soft rocks, support approaches should possess sufficient bearing capacity [31].…”