M. Mbonimpa

Practical pedotransfer functions for estimating the saturated hydraulic conductivity

The saturated hydraulic conductivity k is one of the most important and widely used geotechnical parameters, commonly involved in a diversity of applications. The value of k depends on many factors, which can be divided into three classes: properties of the fluid, pore size distribution, and characteristics of the solid surfaces. Because the latter two are not necessarily constant within a given deposit, the hydraulic conductivity may vary significantly in space. Engineers and scientists need indications about how changing factors may affect the actual k value. In this paper, the authors propose some simple expressions, based on pedologic properties, to estimate the value of k. Using experimental results of their own and taken from the literature, it is shown that the proposed pedotransfer functions can be used for quickly estimating the k value for granular and plastic/cohesive soils. Such expressions can be employed, with a useful chart format, for the preliminary design phase of a project, and also for estimating the range of k values to be anticipated within a given deposit.

Laboratory Column Experiment to Evaluate Oxygen Diffusion through Covers with Capillary Barrier Effects Subjected to Freeze- Thaw Cycles

Environmental reclamation of mine waste disposal facilities often requires their confinement under engineered soil covers to control gas migration and water infiltration. In temperate climates, covers with capillary barrier effects (CCBE) are successfully used to control oxygen flux; these covers require a fine-grained material that acts as a moisture-retaining layer. In Nordic environments, where such natural fine-grained soils are not always available, soil or crushed rock-bentonite mixtures could be used instead. A key parameter in the design and performance evaluation of CCBE is the effective diffusion coefficient of oxygen (D e ) of the moisture-retaining layer. This paper aims at presenting the development of a laboratory column testing and interpretation method to evaluate the D e of a crushed rock-bentonite moisture-retaining layer in a CCBE and the effect of freeze-thaw cycles on D e . The numerical approach used to analyze the experimental diffusion test results allowed obtaining D e for various saturation conditions observed in the moisture-retaining layer. Preliminary results show that the initial measured value of D e increased by two orders of magnitude after 3 freeze-thaw cycles. Steady-state flux calculations based on the obtained D e showed that despite a good initial cover performance, the capacity of the tested cover to act as an oxygen barrier is reduced in the longer term. This study demonstrates that the proposed laboratory column oxygen diffusion test could be an effective tool to assess the performance of CCBE to control oxygen migration when exposed to cold climate conditions.