Advances on the investigation of the hydraulic behavior of compacted GMZ bentonite

Studies on the hydraulic behavior of GMZ bentonite have been performed since 1980s. Based on a review of the former studies, achievements on experimental and theoretic results obtained on the hydraulic aspects of compacted GMZ bentonite are presented in this paper. Results show that, for high suctions (>4 MPa) the water retention capacity of compacted GMZ bentonite is almost independent of the constraint conditions; for low suctions (<4 MPa) the confined samples resulted in significant low water retention. Temperature effects on water-retention depend on constraint conditions and suction. For unconfined samples, the water content decreases with temperature increase at high suctions, while it increases as temperature increases at low suctions. Under confined conditions, the water retention capacity is reduced by temperature rise. The hysteresis behavior is not obvious. Based on the test results, a revised water retention model was developed for considering the temperature effect. The saturated hydraulic conductivity of the densely compacted GMZ bentonite decreases as dry density and temperature increase. Models for prediction of saturated hydraulic conductivity have been developed and verified. With consideration of temperature influence on water viscosity and the effective flow cross-sectional area of porous channels, the model can satisfactorily reflect the temperature effects. The unsaturated hydraulic conductivity of confined densely compacted GMZ bentonite samples decreases first and then increases with suction decrease from an initial value of 80 MPa to zero. The decrease can be attributed to the large pore clogging due to soft gel creation by exfoliation process. The unsaturated hydraulic conductivity of compacted GMZ bentonite under unconfined conditions is higher than that under confined conditions. Under confined conditions, the unsaturated hydraulic conductivity of the highly compacted GMZ bentonite increases with temperature rise. The temperature effect becomes more significant at higher suctions (above 20 MPa). This can be explained by changes of water viscosity and changes of effective cross-section areas of flow channels. With consideration of temperature effects and microstructure changes a revised model for prediction of unsaturated hydraulic conductivity of compacted GMZ01 bentonite was proposed. Verification indicates that the proposed model can give good prediction of the unsaturated hydraulic conductivity of densely compacted GMZ01 bentonite under confined conditions in a suction range of 0-70 MPa. But some deviation occurs in higher suctions (>70 MPa). (C) 2013 Elsevier B.V. All rights reserved.