The study of hydromechanics has identified that surface roughness has an impact on the flow characteristics of single and two-phase fitfids. Technical developments in the field of two-phase flow are of great importance for improving the understanding of underground inundation and gas outbursts, in order to reduce the risks to personnel. The paper describes recent advances in the understanding of two-phase (airwater) stratified flow. A new constitutive model is presented, based upon an extension of Darcy's Law and using the concept of relative permeability. The proposed model is verified by experimental results using 'state of the art' Two Phase High Pressure Triaxial Apparatus (TPHPTA). This study presents the results of laboratory testing that will enable the development of a relationship between roughness (Joint Roughness Coefficient, JRC) and the flow rate for steady state conditions.


Fracture roughness in the form of the Joint Roughness Coefficient (JRC) is acknowledged to have a fundamental impact on the hydromechanical properties of discontinuous media. Previous studies (Barton et al, 1985) have used a series of standard roughness profiles that enable the estimation of fracture hydraulic conductivity. This relationship has also been examined in terms of gas flow (Schrauf & Evans, 1986). With the onset of research into twophase flow, several different approaches have been adopted. A number of studies have considered applied numerical techniques, typically using fractures generated with various mathematical models (Rasmussen, 1991). Laboratory studies have also been carried out using artificial fi'actures (Fourar et al, 1993). The nature of two-phase flow is of practical interest to civil and mining engineering projects especially with regard to the storage of waste in fraetured rock mass and minerals extraction in the mining and petroleum industries.

The aim of the current research program is to study the effect of roughness on fracture aperture and two-phase flow behaviour for both natural and induced fractures, extending over a range of JRC values. A further objective is to evaluate the effect of capillary pressure, phase interference and fracture roughness on the relative permeability and twophase flow behaviour.

In underground rock mass, excavation of multiple openings causestress redistribution and associated fitfid flow through existing and newly created discontintfities. In the Australian coal industry, the risks from gas outburst and groundwater inundation are still only partially understood, and damage to underground eqtfipment and fatalities occur too frequently. The study of two-phase flow characteristics provides a more thorough understanding of nearfield pore pressure variations associated with the redistribution of stresses. Phase interference and the 'blocking-off' of pockets of gas can lead to 1ocalised pressure concentrations that can result in outburst. It is hoped that from the better understanding of fracture characteristics obtained in the laboratory, the field behaviour can be more accurately predicted so that the risks from outburst and inundation can be controlled more effectively.

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