The criterion for discriminating the swelling pressure is the ratio of the the gravity.field to the compressive strength of the rock which is determined emperically. The influences on the compressive strength of clay shale and rock pressure of such factors as the water vibration, dynamic loading caused by Winning and repairs to supports are described, based on practical data. The princeples of support, and preventive measures for weak swelling strata are described. The key is the control of floor heave.
Various types of weak swelling strata occur in many mine areas in China such as Huainan, Shulan, Shenbei and Changguang. These strata differ greatly in their origin, geological age of formation and depth. Also their compressive strengths are quite different. Excavations in these strata become badly deformed and deteriorated by the violent swelling rock pressure, so that frequent repairs are needed, which have a great influence on ongoing production and mine construction. Therefore, it is of vital importance to conduct research on rock pressure and support in roadways built in weak swelling strata.
The deterioration of the roadways caused by the swelling pressure is mainly due to inadequate selection of entry layout and support system by the engineers who did not possess enough data relevant to engineering geology and rock type before excavation and did not realize the nature of the rock pressure in the swelling strata and its harmful effects. Heavy deterioration of the excavation in inevitable under such conditions. In the future, before an excavation is made it is necessary to investigate in detail the engineering geology and make the necessary tests of rock properties. First of all, during design, the entry should not be located in weak swelling strata and in areas of stress concentration. If the roadway has to be driven in a weak stratum, an effective support system should be introduced and Borne strict construction measures should be taken, which might improve the roadway support conditions to a great extent.
Up to now, there is no unified knowledge nor a precise definition of weak swelling rock strata and swelling rock pressure. The BO called weak strata usually refer to those rocks with loose structure, well developed fissures and cracks and low strength. Most of these rocks expand in volume to varying degrees upon wetting, so they are called swelling strata. However, under some mining conditions in the coal mines, even where there is no water, these rocks or clayey rocks with higher strength of up to 600 kg/cm2 would exert violent swelling pressures (e.g. the rock becomes rhological, expands upon being fractured or cracked and causes floor heave).
Based on an analysis of a large quantity of data of the displacements of the soft rock around the excavation, the movement of the surrounding rock is a complex process which involves many factors, including the displacement caused by the expansion of the rock upon wetting,