Effect of a Calcium-Rich Soil on the Performance of an Overlying GCL

Changes in geosynthetic clay liner (GCL) properties over time are examined for the case in which the GCL (1) rests directly on a ${\mathrm{Ca}}^{++}$ rich soil ($1,700–1,800\mathrm{mg}/\mathrm{l}$ ${\mathrm{Ca}}^{++}$) and (2) a 30 cm foundation soil ($200–300\mathrm{mg}/\mathrm{l}$ ${\mathrm{Ca}}^{++}$) overlying the ${\mathrm{Ca}}^{++}$ rich soil. Results for a control case in which the GCL rested only on the foundation soil are also reported. The moisture content increased to 108% and then remained constant in the control case. The moisture and calcium uptake from the underlying soil caused the moisture content of GCL to increase to 96 and 86% in the first 279 days of the experiment for the cases with and without foundation soil, respectively. The moisture content then decreased to 80 and 67% after 1,100 days under isothermal condition with and without the foundation layer, respectively. After 1,100 days (three years), the hydraulic conductivity of the GCL increased (attributable to cation exchange) from approximately $3\times {10}^{-11}\mathrm{m}/\mathrm{s}$ initially to approximately $7\times {10}^{-11}$ and $2\times {10}^{-10}\mathrm{m}/\mathrm{s}$ with and without the foundation layer. Changes in swell index (SI) and exchangeable cations were measured and correlated to changes in hydraulic conductivity.