Backfill leachate hydration effects on composite polymer-amended GCLs in vertical cutoff walls: swelling and hydraulic conductivity
摘要
Swelling behavior and hydraulic performance of geosynthetic clay liners (GCLs) govern the long-term effectiveness of GCL composite vertical cutoff walls for containing municipal solid waste (MSW) leachate-contaminated groundwater in dumpsites and uncontrolled landfills. However, the effects of hydration with different backfill leachates on swelling behavior and hydraulic performance of GCLs have not yet been systematically explored. This study investigated one-dimensional swelling strain and pressure of composite polymer [i.e., polyanionic cellulose (PAC) and hydroxypropyl methylcellulose (HPMC)]-amended GCLs (PHGCLs) hydrated with three types of leachates extracted from three backfills. Moreover, the hydraulic conductivity (k) of GCLs hydrated with the backfill leachates was evaluated using MSW leachate as the permeant. Unamended GCLs were tested for comparison. Results showed the PHGCLs exhibited increases in final swelling strain of 90–310% and final swelling pressure of 40–57% relative to the unamended GCLs. The most pronounced swelling responses of PHGCLs and unamended GCLs were observed under hydration with soil–bentonite (SB) backfill leachate, whereas the weakest responses occurred with soil–cement–bentonite (SCB) backfill leachate. Consistently, the PHGCL hydrated with SB backfill leachate possessed the lowest k (2.9 × 10–11 m/s), while that hydrated with SCB backfill leachate exhibited the highest (4.1 × 10–11 m/s). PHGCLs showed lower k values than unamended GCLs (2.9 × 10–11–4.1 × 10–11 m/s vs 1.7 × 10–10–8.2 × 10–10 m/s). The k was inversely correlated with swelling strain and swelling pressure of unamended GCL and PHGCL.