An Investigation in to Compaction, California Bearing Ratio and Shear Strength Behaviour of Coal Mine Overburden Dump Material Mixed With Fly Ash

Compaction, California Bearing Ratio (CBR) and shear strength behaviour of coal mine overburden dump material and fly ash mixed overburden dump material are studied by conducting a series of tests as per the standards. Test results are compared and analyzed to observe the changes occurred due to addition of fly ash and also to check the suitability of the mixture for various geotechnical applications viz. for road construction near captive coal mines and also as a fill material in the voids of open cast coal mines by mixing it with the overburden dumps. This investigation reveals that fly ash should be mixed in the range of 12.5% to 15% by mass (approx. 18% to 22% by volume) in the OB dumps, so that they can be compacted over a wide range of moisture content with very little variation in its unit weight. The test result also reveals that cohesion of OB dump material increases and friction angle reduces with the increase in fly ash content. The stress-strain behaviour of the overburden dump material and fly ash mixed overburden dump material exhibited post-peak softening behaviour.