Abstract

The stability of mine overburden dumps is crucial for the proper functioning of surface mining activities. The physical characteristics of dump constituents influence their shear strength. Currently, no technology or suitable method is found in the literature for accessing porosity or compactness without coring inside the intact dump materials. The presented study investigates the compaction behaviour of dump constituents of an active overburden dump mostly composed of weak shale. Field and laboratory experiments are designed to determine the parameters of an analytical relationship between the porosity of shale with the height of the overburden dump. Tests conducted include sand replacement method, proctor test, and triaxial shear tests in consolidated drained condition. It is found that the porosity decreases in the vertical direction from top to bottom of the dump, represented by a negative exponential distribution. The exponent of this distribution, termed as “mechanical pseudopore compaction coefficient” and represented by βm is estimated based on the laboratory and field experiments. It is now possible to estimate the distribution of the porosity across the depth of the dump, knowing the porosity on the surface of the dump. The paper presents detail description of the experimental procedures for estimating the changes in porosity of a dump with its height.

Introduction

The ever increasing demands in mineral and energy sectors have led to increase in mining activities. The operations involve extraction of overlying earth materials composed of Soil-Rock Mixtures (SRM) referred to as overburden dumps (Fig. 1). The earth materials are heterogeneous and loose geomaterials that consist of particles varying widely in sizes, ranging from boulder to clay (Gao et al., 2017; Shrivastava et al., 2021). The dump materials are stacked into layers in the nearby areas, and management of these dumps are crucial for the efficient mining of ore deposits. As per the Ministry of Coal, Government of India, the annual removal of overburden dump in the year 2020-21 was 1926 million cu. meter. To accommodate these massive amounts of overburden dumps in constraint leased lands, mine managements often decide to increase the height of dumps.

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