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For the past few decades, there has been an intense public and scientific concern over the disposal of solid and hazardous waste, which hampers the harmony of the ecosystem. The disposed off waste in the due course of time interacts with rainwater and contaminates the ground water resource. Such a situation calls for proper understanding and modeling of the long-term performance of these wastes and their transport through the porous media. With this in view, an attempt was made to model advective-diffusive transport of a nonreactive contaminant (chloride ion) through the unsaturated silty soil, in a geotechnical centrifuge. The results were compared with those obtained from the finite element analysis using SEEP/W and CTRAN/W, and an excellent matching between the results has been noted.

A two-dimensional finite difference model, which solves mixed type of Richards’ equation, whose non-linearity is dealt with modified Picard’s iteration and strongly implicit procedure to solve the resulting equations, is presented. Modeling of seepage flow through heterogeneous soils, which is common in the field is addressed in the present study. The present model can be applied to both unsaturated and saturated soils and can handle very dry initial condition and steep wetting fronts. The model is validated by comparing experimental results reported in the literature. Newness of this two dimensional model is its application on layered soils with transient seepage face development, which has not been reported in the literature. Application of the two dimensional model for studying unconfined drainage due to sudden drop of water table at seepage face in layered soils is demonstrated. In the present work different sizes of rectangular flow domain with different types of layering are chosen. Sensitivity of seepage height due to problem dimension of layered system is studied. The effect of aspect ratio on seepage face development in case of the flow through layered soil media is demonstrated. The model is also applied to random heterogeneous soils in which the randomness of the model parameters is generated using the turning band technique. The results are discussed in terms of phreatic surface and seepage height development and also flux across the seepage face. Such accurate modeling of seepage face development and quantification of flux moving across the seepage face becomes important while modeling transport problems in variably saturated media.

This paper explores the hydro/mechanical behaviour of unsaturated engineered buffer. This is achieved via the assessment of a conceptual model for micromacro moisture flow. In particular the re-saturation behaviour of a large scale insitu experiment performed by Atomic Energy of Canada Limited, (AECL), is examined. Numerical simulations of the test are presented and the conceptual model investigated.

The experiment, known as the isothermal test, examines water inflow, from the surrounding rock, into highly compacted, unsaturated buffer material. Numerical simulations of the experiment are performed using an approach developed to model the thermo/hydraulic/mechanical behaviour of the system. The simulation of the experiment, using a “conventional” approach to describe the hydraulic conductivity of the buffer material, revealed that neither the duration nor the pattern of moisture influx could be modelled accurately. Further study suggested incorporation of a conceptual model for micro/macro moisture flow via the conductivity relationship may explain the experimentally observed behaviour. This approach yielded significant results with both the pattern and the rate of water uptake being simulated with a much greater accuracy.

The computer code CODE-BRIGHT has been applied to simulate thermal-hydro-mechanical (THM) experiments on clays being considered as host rock and as buffer/backfill for the disposal of radioactive wastes. In this paper, two modelling exercises will be presented: (1) prediction of the hydration of bentonite, and (2) scoping calculation of large-scale heating tests to be performed with a bentonite-filled clay cylinder in order to study coupled THM processes taking place in the near-field of heat-generating wastes in drifts and boreholes. The results suggest that the coupled THM phenomena observed in the laboratory can be well represented and interpreted by numerical simulation with the code.

This paper presents a case history of an unsaturated soil seepage analysis for design of a soil cover system to promote saturation within a mine tailings deposit. A gold mine tailings facility in Canada is being closed. The tailings facility consists of perimeter dykes containing tailings with a pond in the central area and a tailings beach along one perimeter dyke. Water quality will be enhanced by reducing the volume of material exposed to oxidation along the tailings beach. An engineered soil cover was considered as an option to maintain tailings saturation and therefore reduce oxidation along the beach. Numerical analyses were conducted to estimate surface water infiltration rates and corresponding saturation and ground water elevations in the tailings. A one-dimensional finite element software, SoilCover, was used to simulate the beach surface infiltration with various cover options. The net infiltration rates obtained from the SoilCover model were then used as input parameters for a subsequent two-dimensional finite element seepage analysis. The 2-D seepage analysis was conducted using a computer software, Seep/W, to determine ground water level and seepage quantities. Transient state analyses were conducted to evaluate ground water levels in response to construction activities and weather condition changes. A practical cover option was selected based on the analysis results. The groundwater levels predicted in the beach and perimeter dyke agreed with the piezometer data, which confirmed the infiltration rate obtained from the SoilCover model and the results from the Seep/W model.