Hydraulic Conductivity Determination of Compacted Sand-Bentonite Mixture Using Filter Press

Abstract

Abstract This paper presents a method to adapt a measurement in order to enhance its exploitation time and provide a suitable comparison with standard permeability tests. The filter press apparatus used for the fluid loss test (FLT) was selected to elaborate a hydraulic performance method, which is used for compacted sand-bentonite mixtures. An analytical method was developed for hydraulic conductivity determination. Material and test parameters (hydraulic pressure Po, hydraulic gradient i, hydraulic conductivity ko, and α coefficient) were highlighted. Series of experiments were performed with a filter press and rigid wall permeameter (RWP). The hydraulic study was performed on samples composed of soil with 2 %, 3.5 %, and 5 % of an activated Ca-bentonite permeated with a weakly 1×10−3 M NaCl. An improved FLT (IFLT) leads to a differentiation of the effect of clay concentration on hydraulic conductivity, but it is not suitable enough to estimate the hydraulic conductivity value as the RWP. Direct test comparisons between RWP and IFLT show hydraulic conductivity values of the same order of magnitude. Sample compaction is known to reduce the void ratio variation. However, thickness variation may occur during testing due to a combination of swelling and consolidation effects caused by the hydraulic head. Then, the mechanical behaviour of the compacted sample was investigated with an oedometer. The IFLT method could provide rapid hydraulic performance indication compared to standard permeability tests. Further investigations would be needed to properly take into account the mechanical effect of the pressure.