Effect of Gradation, Gravel Content and Fragment Size on the Compaction and Shear Strength Behaviour of Coal Mine Overburden Dump Material

摘要

An understanding of the shear strength characteristics of geomaterials forming overburden dumps in coal mines is required for assessing the stability of overburden dumps. The effective shear strength of dump materials depends on a wide variety of interrelated parameters including: intact particle strength, particle angularity, gradation, compaction density, water content, degree of saturation, and others. The decrease in particle sizes and the production of clay and silt size fractions due to weathering may result in a change in the shear strength properties of the mine rock and alter the physical stability of the mine rock structures. Shear strength behaviour of overburden rock for dump slope design is generally carried out by small scale laboratory testing using standard size triaxial and direct shear test apparatus on mostly sand and silt size fines passing through 4.5 mm sieves due to limitations on the size of the testing equipment. The influence of coarser fraction of rock fragments present on the overburden dumps on its shear strength is not taken in to consideration. These shortcomings lead to uncertainties associated with the assignment of accurate shear strength parameters for slope stability modelling and design. An investigation is here carried out to assess the effect of presence of coarser rock fragments and gradation on shear strength behaviour of the coal mine overburden dump rock material by conducting a series of small and large scale consolidated drained direct shear test.