FACTORS AFFECTING GCL SELF-HEALING AND ITS SUBSEQUENT HYDRAULIC PERFORMANCE

Abstract

A number of researchers have studied GCLs’ self-healing capacity, however, most examined either regular holes or relatively benign hydrating/permeating fluids not representative of typical field applications. This thesis addresses this gap by firstly investigating the self-healing of regular holes/slits when hydrated from: unlimited benign and simulated cation rich pore fluids, subgrade with pore fluid limited by the subgrade gravimetric moisture content. The thesis then examines the self-healing of irregular holes/slits formed by downslope bentonite erosion in both laboratory and field experiments when rehydrated on Godfrey silty sand (GSS). Additionally, the hydraulic performance of GCLs after self-healing was assessed for specific scenarios. The hydrating fluid chemistry was found to impair the self-healing capacity of GCLs with regular holes/slits under both relatively ideal conditions where there was sufficient hydrating fluid available (simulating pond applications) and conditions where GCLs hydrated from GSS with only limited hydrating fluid available from the pores (simulating common field conditions) and increased hydraulic conductivity due to cation exchange. This was corroborated by findings from a control test on silica sand with similar characteristics to GSS. The results suggested that when designing a containment facility, holes smaller than 15 mm-diameter are able to self-heal and not likely to have a significant impact on the hydraulic performance of the liner system, while holes greater than 25 mm-diameter should be of concern to designers. Field eroded GCL specimens with irregular holes/slits showed notably less self-healing than laboratory eroded and virgin GCL specimens when rehydrated from GSS with limited pore fluid, owing largely to the cation exchange the bentonite had experienced in the field. The post-hydration hydraulic conductivity of GCL specimens with holes/slits was about 1~4 orders of magnitude higher than that of an intact specimen. For a 0.3m design hydraulic head, a single or few such eroded holes/slits may not be of a great concern in terms of increase in leakage monitoring, however, that would change if there were many (e.g. 100) or much longer (e.g. 10~20 m-long) defects per ha, which may not be acceptable for containing landfill leachate.