Geomechanical Aspects of Gas Outbursts in Louisiana Salt Mines

Abstract

Gas outbursts in Louisiana salt mines are sudden eruptions of salt and gas from the face or roof of a mine heading that result in a generally semiellipsoidal cavity with axial length of up to 50 m or more. The potential risks from gas outbursts include loss of life or even the mine. Several characteristics of gas outbursts in Louisiana salt mines and suggested methods for their prevention are common to both coal mines and other salt mines. The objectives of this paper are to synthesize the available knowledge of the geomechanical aspects of gas outbursts, suggest a plausible mechanism for gas outbursts in Louisiana salt mines, recommend procedures for prediction and prevention of the outbursts, and outline the needs for further study in this important area of geomechanics. In Louisiana salt mines, a gas outburst occurs at a certain depth when a heading face approaches a pressure pocket (impure or altered salt with entrapped, high-pressure gas). It is proposed that a gas outburst is initiated by disking in biaxial compression and propagates by spalling of the cavity walls and further disking. The outburst is terminated by a combination of dilatancy hardening, increase in stress along the cavity axis, andmore » enlargement of the cavity to the boundaries of the pressure pocket. Identification of burst-prone areas will require research into in situ measurement of material characteristics and further understanding of the mechanism of gas outbursts. Shock blasting in advance of mining appears to be a promising technique for controlling gas outbursts.« less