Experimental study of brown coal hydraulic behavior at low confining stress

The hydraulic behavior of Victorian brown coal has been studied under low pressure confining conditions. A triaxial constant head permeameter was constructed to carry out permeability tests under alternative confining conditions. Test results from alternative constant head test methods were found to be different indicating higher than expected internal storage due to the possible existence of gas in the coal matrix and/or compressibility of the coal grains. A conceptual model of brown coal with disconnected gas bubbles was proposed to explain the observed variation of hydraulic behavior. In this model, the compressible gas bubbles are assumed to be trapped between compressible coal particles. A numerical model was developed to gain insights into the hydraulic influence of these factors and the model was used to simulate the test process. Constant hydraulic conductivity was assumed. The results from the model and the tests are found to compare well. The model explains most but not all of the observed behavior.