| Analyses presented in this study provide a new method for obtaining a hydraulic conductivity of bentonite and insight into the factors that can influence the test. The ‘modified fluid loss test’ (MFL) was developed to measure hydraulic conductivity from the filter press. Based upon the modifications of conventional filtration models, the average hydraulic conductivity of a bentonite filter cake could be obtained from rate of filtrate-time relation and the water content of filter cake. For the pressure range associated with typical bottom liners in solid waste landfills (>100 kPa) the hydraulic conductivities from MFL method showed higher (conservative) values than those from flexible wall permeameter (FWP). The modified fluid loss test was found to be an effective test method to assess the hydraulic conductivity of bentonite, especially at low effective stresses. The MFL test can be used to obtain the hydraulic conductivity of bentonite within a few days instead of weeks for the FWP test.;The free swell test, the fluid loss test, and the MFL test were performed for three bentonites with distilled deionized water (DDIW), NaCl, CaCl 2, and LaCl3 solutions under different pressures in order to investigate the influence of chemical solutions and effective stress on hydraulic properties. In solutions with low cation concentration, the free swell index exhibits an increasing trend with increasing concentration before the diffused double layer fully collapsed at higher concentration. Decrease of void ratio, increase of hydraulic conductivity with increasing cation concentration in MFL test is assumed to be due to the pore characteristics of bentonite in solutions. Increase of hydraulic conductivity and decrease of void ratio resulting from increasing cation valence and concentration could be identified. The same slopes of linear relations between hydraulic conductivity and effective pressure on a log k-log p plot indicates that varying the cation solution changes hydraulic conductivity, but variation does not change the slope of log k-log p relationships. From the results of three index tests for a bentonite with real-soil-solutions extracted from sub soils and cover soils of GCL placed at test site, the MFL test gives useful and consistent information about the hydraulic behavior of bentonite. |
