EVALUATION OF IN-SITU STRENGTH AND SETTLEMENT CHARACTERISTICS OF MUNICIPAL SOLID WASTE

Abstract

National University of Sciences and Technology (NUST) is setting up its campus in sector H-12. The area covered by Municipal Solid Waste (MSW) covers the north western extent of the sector. In view of the scarcity of land and increased interest in the planning for future use, it was felt necessary to evaluate the geotechnical aspects of the MSW dump for its optimum utilization in future. A detailed geotechnical site investigation was carried out for evaluation of strength and settlement characteristics of the recently MSW dump site of Islamabad Capital Territory located at sector H-12 Islamabad, Pakistan. The MSW is spread over approximately 25 hectares with varying thickness of 0.5-2.5 meter over a natural ground surface. Original stratum comprises of 0.25 to 10 meter thick lean clay / silty clay overlying bedrock. Thinly bedded shale / sandstone rocks are present in a slightly weathered to highly weathered state below the clay / silty clay deposits. Given the level of variability in waste composition, state and degree of degradation, the use of generic data currently available in the literature cannot be considered acceptable or reliable for all sites or applications. Determination of site specific characteristics is a necessity. A series of field testing was designed for in-situ testing of MSW. Five Electrical Resistivity Tests (ERTs) coupled with auger holes and test pits were carried out to establish depth profile of natural ground under the MSW. Six in-situ large scale direct shear tests were carried out. An especially fabricated in-situ large scale direct shear box measuring 1.22 meter x 1.22 meter was used. Each direct shear test was carried out with normal stresses of 6, 13 and 20 kPa. MSW has negligible cohesion and the angle of internal friction ranges from 16 degrees to 26 degrees. Four plate load tests were carried out with different plate sizes. In all the cases, the settlement increased almost linearly with an increase in stress / load. The solid waste from the sheared test samples was tested for in-situ unit weight, dry moisture content and was then characterized physically. The unit weights varied from 5.29 kN/m3 to 12.199 kN/m3, moisture content ranged from 23 percent to 37.7 percent; and the samples were found to have varying composition of fines, polythene bags, concrete/ bricks/ stone debris, household paper, wrappers, broken glass and utensils, animal bones, cloth, canvas, leather, plastics, scrap wood and indistinguishables.