Soil-water characteristic curve of a dual porosity waste rock from coal mine

Soil water characteristic curve for coarse granular materials are not usually important for mechanical and hydraulic geotechnical analyses, so there is a scarce literature data, but dual-porosity granular materials can develop unexpected significant suction values related to the micro pores response on drying. A laboratory and pilot scale field research on dry cover alternatives for acid mine drainage control in a coal mine in South Brazil required soil water characteristic curve data of the waste rock to be covered for water balance modeling. The soil water characteristic curve of the waste rock obtained in the numerical models by pedofunctions of the material grain size distribution data did not result in good prediction of the observed field behavior. The soil water characteristic curve of waste rock was then determined in the laboratory for waste rock samples collected from the mine waste pile and from one of the experimental cells of the pilot test installation. The soil water characteristic curve of the waste rock was determined in the laboratory by the suction plate method with drying procedure for reconstituted samples, and with a T5 Delta-T mini tensiometer in undisturbed waste rock samples previously saturated for 24 hours and air dried along different time intervals. The experimental curves are compared to the predicted curves based on the material grain size data, and the adjustment by theoretical model using RETC program clearly shows a dual porosity behavior in the soil water characteristic curve of the waste rock.