Poster Presentation Australasian Groundwater Conference 2017

An aquifer becomes an aquitard: centrifuge measurement of desaturating sandstone from the constrained zone above an underground mine (#92)

Paul Cai 1 , Wendy A Timms 1 2 3 , Martin S Andersen 2 4 , Noune S Melkoumian 5
  1. UNSW School of Mining Engineering, Sydney, NSW, Australia
  2. Connected Waters Initiative Research Centre, UNSW Australia, Sydney
  3. Australian Centre for Sustainable Mining Practices, Sydney, Australia
  4. UNSW School of Civil and Environmental Engineering, Sydney, Australia
  5. University of Adelaide, School of Civil, Environmental and Mining Engineering, Adelaide, Australia

Perched aquifer conditions often develop in the constrained zone overlying underground mines, due to dewatering of the mine workings. An inverted water table marks a transition from saturated un-fractured sandstone to an underlying unsaturated fractured zone. The objective of this research was to identify the relationship between vertical hydraulic conductivity (Kv), saturation (S) and suction (p) for a sandstone. 

An AllegraX‑15R centrifuge was fitted with custom made drainage cells (n=4) to test discs of sandstone (50 mm diameter, 5 mm thick) initially at >95% saturation with fresh water. The centrifuge speed was accelerated to provide increasing tension and drainage (300 to 2800 revolutions per minute), with the mass of drainage at the base of each cell measured after each acceleration step. The reduction of Kv with decreasing saturation (S) was observed for the sandstone (n = 8). On average, relative Kv values decreased by a factor of 10, as moisture content decreased from 16% (at maximum saturation) to 13%. For several sandstone samples, a small decrease in moisture content of 1-2% was associated with a 50% reduction in Kv values.

An empirical relationship of the volumetric water content (V), V = 0.015e^0.02p (r2 = 0.9) was developed as a function of the suction (m H2O) applied within the centrifuge. To our knowledge this is the first time such relationships have been developed for consolidated rock. Further research is recommended to verify these observations and to model transient and non-linear drainage processes to calculate actual Kv values. These empirical relationships could be used to improve numerical models that include semi-saturated matrix flow processes. This research has demonstrated that partial desaturation significantly decreases the permeability and that the base of aquifers overlying mine workings can effectively become aquitards.

  • We are offering awards for Career and Early Career presentations and posters. Please indicate length of time since highest degree completed.: 0 to 5 Years or currently studying
  • We are offering awards for Career and Early Career presentations and posters. Please indicate length of time since highest degree completed.: 0 to 5 Years or currently studying