Performance Evaluation of Coal Ash-Based Barriers of Landfill Covers

Abstract

The objective of this paper is to evaluate the performance of coal ash-based barriers subjected to continuous differential settlements in a geotechnical centrifuge. Motor-based differential settlement simulator was used to induce differential settlements with a distortion level up to 0.125 at 40 gravities in a 4.5 m radius large beam centrifuge facility available at the Indian Institute of Technology Bombay, India. A short series of centrifuge model tests were conducted by varying the thickness of coal ash-based barriers. All the developed coal ash-based barriers were subjected to an overburden of 25 kN/m2 equivalent to that of the landfill cap covers. All the models were thoroughly instrumented with linearly variable differential transformers (LVDTs) and Pore pressure transducers (PPTs) to measure vertical settlements and pore water pressure. Digital image cross-correlation (DIC) technique was adopted to arrive at deformation profiles of coal ash-based barriers and strain distribution along the topmost surface of the tested barrier during all settlement stages. The water sealing efficiency was assessed in terms of limiting distortion level and strain at water breakthrough. A 0.6 m-thick coal ash-based barrier with an overburden of 25 kN/m2 was observed to experience a limiting distortion level of 0.068 and a strain at breakthrough of 0.98%. In comparison, a 1.6 m-thick coal ash-based barrier has not registered any water breakthrough and been noted to sustain large deformations. This centrifuge study demonstrates that coal ash-based barriers of an adequate thickness can be used as impervious barriers in landfill cap covers.