Hydraulic performance of geosynthetic clay liners under gravel cover soils

Hydraulic performance of adhesive-bonded and needle-punched geotextile-supp orted geosynthetic clay liners (GCLs) was measured for specimens covered wi th uniformly graded fine, medium, and coarse gravel using flexible-wall per meameters. Local measurements of specimen thickness, water content, and mas s per unit area were taken after each test to quantify thickness variabilit y and bentonite migration/consolidation behavior. Control rests were also p erformed to measure GCL hydraulic performance under conventional testing co nditions. Test results showed that the hydraulic performance of control and gravel-covered specimens of both GCL products improved with increasing con fining stress. In addition, measured values of hydraulic conductivity for t he gravel-covered specimens were less than the manufacturer's specification . The amount of bentonite migration generally increased with increasing cov er soil particle size and rate of loading. Thickness variability and benton ite migration were generally less for the needle-punched product, which is attributed to the additional confinement provided by the reinforcement. The placement of an additional non-woven geotextile over the adhesive-bonded G CL was somewhat effective in reducing thickness variability and bentonite m igration under rapid loading conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.