A NEW LABORATORY MODEL OF A SLAKING CHAMBER TO PREDICT THE STABILITY OF ON-SITE COAL MINE SPOILS

Abstract

Slope failures of spoil piles pose a significant safety risk in open-cut strip mining due to
slaking over time due to overburden pressure and water saturation. Most spoil pile failures occur when the
pit has been previously filled with water and then subsequently dewatered. It is important to understand how
the mechanical properties of base spoil material are affected by slaking when designing safe spoil pile slope
angles, heights, and dewatering rates. A new laboratory slaking chamber (360mm ID, 400mm high with
20mm wall thickness) has been designed and constructed to accommodate approximately 60 kg of spoil (unit
weight, 18 kN/m3) and a simulated overburden pressure of 1000 kPa. Consolidation of the spoil can be
measured through a linear variable differential transformer (LVDT) attached to the system. Using this
apparatus, a fresh spoil material collected from a coal mine in Brown Basin Coalfield of Queensland,
Australia was subjected to high overburden pressure (0 – 900 kPa) under saturated condition and maintained
over a period of time (0 – 6 months) allowing the material to slake and successfully tested for classification,
permeability, and strength properties. Results suggested that the slaking of saturated coal mine spoil increase
with overburden pressure and the time duration over which the overburden pressure was maintained. Shear
strength and permeability of spoil decreased with increase in spoil slaking.