Design and control of large hydraulic backfill pours : CIM Bull, V75, N838, Feb 1982, P102–111

Abstract

This paper outlines the procedures to be followed for large, semi-continuous cemented or uncemented hydraulic backfill pours to ensure a minimum of delay in the mining sequence and provide the necessary control for safety purposes. The drainage requirements for given backfill material and site conditions can be readily calculated and hence adequate drainage facilities can be incorporated in the backfill and bulkhead designs. The analysis of the pressures acting at the base of large filled stopes indicates that free-draining bulkheads can be used in a majority of situations. Typical design calculations for poured reinforced concrete, free-draining timber and pervious concrete block bulkheads are presented. Operational control of pouring operations requires periodic checking of the input material properties, water balance measurements and solid plus water pressure measurements. Hydrostatic pressure cannot develop within a fill mass provided that the quantity of water flow from the exits is, at all times, equal to the quantity of water flow arriving at the base of a free-draining backfill. The use of filter blankets above any waste rock or slough in the restricted cone area and the use of fiber material in the drift plugs ensure adequate base and exit flow quantities. Solid and seepage pressures acting on a bulkhead can be estimated from the fill properties, the geometry of the stope void and the exits. Free-draining timber or concrete block bulkheads can be readily designed to provide an adequate factor of safety. These designs result in definite economic advantages over massive concrete bulkheads and reduce significantly the time between extraction and filling cycles. Significant deviations from expected performance can be readily identified and, in the limit, the necessary safety factor can be maintained by stopping the pour. If the procedures outlined are followed, there is no possibility of failure of a free-draining bulkhead.