Evaluation of geogrid as a reinforcement layer in clay based engineered barriers

Imperviousness of clay based barrier, which is provided in cover system of low-level radioactive waste disposal sites, is essential to mitigate the environmental hazard. The objective of this paper is to examine the influence of geogrid reinforcement on the deformation behaviour of clay based cover systems subjected to differential settlements. A series of centrifuge tests were performed on model clay barriers with and without the inclusion of geogrid reinforcement at 40 gravities. Motor-based differential settlement simulator was custom designed and developed for inducing continuous differential settlement in high gravity environment. By maintaining type and location of the geogrid within the clay barrier as constant, the thickness of clay barrier is varied. The performance of the clay barrier with and without geogrid layer having an overburden pressure equivalent to that of cover system was monitored by measuring water breakthrough at the onset of differential settlements. It was observed that both 0.6 m and 1.2 m thick clay barriers with and without overburden experienced cracks extending up to full depth. In comparison, geogrid reinforced clay barrier was found to sustain large distortions with an enhanced imperviousness. With the provision of an overburden equivalent to that of cover system, integrity of geogrid reinforced clay barrier was found to be retained even after inducing a distortion level of 0.125. This implies that provision of thickness of clay barrier equal to 0.6 m reinforced with a suitable geogrid may be adequate in sustaining higher distortion levels.