Observations made at Goat Meadows - a small sub-alpine basin located near Pemberton, British Columbia -demonstrated that a layer which is either water repellent or has only a limited affinity for water is present at most vegetated sites. The layer is typically a few centimetres in thickness, and is usually located at or near the top of the profile: it was present only in the zone of accumulation of organic matter. The spatial distribution of the layer did not appear to be related to the distribution of any particular species of plant. Sampling of sub-alpine sites in the Cascade, Selkirk, and Purcell Mountains indicated that such layers are common in the alpine - sub-alpine ecotone of southern British Columbia. The relationship between ponding depth and infiltration rate was explored through experiments conducted on samples collected near Ash Lake, in Goat Meadows. These samples were chosen for analysis because the repellent layer was in excess of thirty centimetres thick at this site. Infiltration rates remained below 2x10⁻⁹ m/s for all samples, even given ponding depths of up to forty centimetres. Breakthrough of liquid water was not observed, even after one month, which implies that most of the infiltration occurred as vapour transfer. In order to observe the movement of liquid water through water repellent media, a plexiglas cell was constructed. A synthetic water repellent sand with uniform surface properties was used as the medium. It was found that up to some critical depth, there was no entry of water into the medium. As the ponding depth was increased in steps, the front would advance in steps: it remained stationary between these step-increases in ponding depth. As the front advanced, protuberances or "fingers" began to develop. At some critical ponding depth, a finger would grow without bound. These observations pose a challenge to existing models of infiltration, since it appears that heterogeneity at the scale of individual pores must be invoked to explain them, but it is usually assumed that the properties of a porous medium are continuous at this scale. The thermodynamics of filling and emptying of pores is considered with emphasis on the effects of pore shape and of variations in the physicochemical properties at the scale of the pore. This thermodynamic analysis provides the conceptual basis for development of a model of infiltration in which pore-scale heterogeneity is preserved. Although it was not developed as such, the model follows the approach of cellular automata, in which local relations between pores or "cells" govern the behaviour of the system. The model replicated the observations of infiltration into synthetic water repellent porous media well: both the halting advance of the front as the ponding depth was increased and the development of fingers were simulated. The fact that such complex behaviour was predicted using only a simple set of physically based rules confirms the power of the approach. / Arts, Faculty of / Geography, Department of / Graduate

Seepage barriers have been used extensively to mitigate seepage problems in dams and levees. Although the designs of many of these dams and levees have been based on intact seepage barriers, seepage barriers have been shown to be susceptible to deformation and cracking when high differential hydraulic pressures act across the barrier. Cracking and deformation have also been observed due to thermal expansion and contraction during seepage barrier curing. Under certain conditions, a crack can lead to serious seepage problems, which could potentially lead to the development of a low-resistance seepage pathway. Three scenarios have been identified where there is potential for erosion to occur adjacent to a crack in a barrier: 1) erosion at the interface between a fine-grained soil and a course-grained soil, 2) erosion of overlying soil due to flow along a joint in bedrock, and 3) erosion of the barrier material itself. Previous studies have investigated the first mode of erosion and studies are underway to look into the second mode. The objective of this study is to investigate the third mode of erosion and to identify the conditions under which serious seepage problems can develop. The question considered was whether the combination of highly permeable material adjacent to a crack in a seepage barrier and a large differential head across the barrier combine to develop a velocity within the crack that is erosive to the seepage barrier material. Laboratory tests have been performed on a variety of seepage barrier materials to assess the potential for cracks to develop a preferred seepage path leading to a serious seepage problem. The results of this study will be useful in risk assessment studies of dams and levees with existing seepage barriers as well as in the design of new seepage barriers. Having knowledge of the conditions under which problems may occur will aid in the selection of seepage barrier types for new barriers, placement of instrumentation to monitor new and existing barriers, and mitigation of existing barriers where problems have been identified. The data provided will assist engineers in quantitatively assessing the potential for the propagation of critical seepage problems from cracks in seepage barriers.

No description available.

The residual flow procedure (RFP) is used to conjunction with finite element method for solution of steady state free surface seepage in dams containing open cracks. The cracks are simulated using the thin-layer element concept. A comprehensive parametric study is performed to analyze the applicability of the numerical procedure with the thin layer element. Here, vertically trending as well as horizontally trending open cracks are considered with variable lengths, widths, and conductivities. It is found that the numerical results involve oscillatory, unstable, and physically unreasonable behavior beyond critical values of the geometry and conductivities. Here, the vertically trending configurations are found to be relatively more sensitive than the horizontally trending configurations. Although additional research will be needed to analyze other factors such as different crack geometries, transient flow, and different ratios of crack conductivities to surrounding soil conductivities, the results presented here suggest that the procedure can be applied for seepage analysis in dams containing open cracks.

Dams are among the most critical of civil engineering structures and are susceptible to damage due to seepage. Geomembranes have been used to minimize seepage problems in dams since 1959. However, geomembranes are vulnerable to damage, in the form of tears and punctures, during installation and throughout the service life. These defects impact the effectiveness of a geomembrane as an infiltration barrier resulting in leakage through the geomembrane liner and into the body of the dam. The majority of previous studies conducted to investigate leakage through defects in geomembranes considered heads below 0.3 m, which corresponds to flow for conditions experienced by landfill liners. The main objectives of this study were to quantify the leakage rate through defects in geomembrane lining systems for dam and to evaluate the implications of the leakage on the performance of dams. Experimental, analytical and numerical studies were conducted as part of this investigation. The experimental testing program included permeameter cell tests for the following lining systems: i) geomembranes over clay layers, ii) geomembranes over sand layers and iii) geomembranes over geosynthetic clay liners. The permeameter tests were conducted to investigate the effects of soil type, initial water content, dry unit weight and hydraulic head on leakage through a defect in a geomembrane liner. The analytical component was conducted to evaluate the transmissivity at the interface and radius of wetted area for the tests conducted as part of the experimental component. The numerical component of this study was performed using the finite element method to simulate the experimental tests and the performance of actual dams. Ultimately, the laboratory tests and subsequent analyses were used to develop a set of tools (e.g., empirical models, design recommendations) that are expected to assist engineers in the design of geomembrane lining systems for dams. Also, the study was used to identify and address potential concerns (e.g., global stability) that may result in failure of systems in which geomembrane liners are used. This study is expected to contribute to a better understanding of the performance of geomembranes as dam liners. The presence of a geomembrane, even with a defect, was found to reduce the amount of leakage that occurs through a soil layer. New predictive equations were developed to estimate leakage through defects in composite lining systems. The finite element analyses indicated that a dam with a geomembrane with very large defects would not develop pore pressures that were similar to those observed for an unlined dam. The factor of safety for the unlined dam was improved by the placement of a geomembrane on the upstream face. Consequently, a geomembrane may also eliminate the need for a blanket drain at the downstream toe, which could decrease the cost of construction. / text

No description available.

The clogging of fine-porosity geotextiles by soil particles is considered to be a problem in applications of these fabrics to filtering of municipal and industrial effluents. However, the clogging phenomenon can be an advantage for certain purposes, such as the creation of near-watertight membranes for sealing manure holding tanks. The conceived advantages of non-woven needle-punctured geotextiles are that they are less expensive due to lower material quantity, they are more resistant to tensile stresses compared to impermeable plastics and concrete, and they are easily installed. This thesis describes experimental work on the permeability and clogging characteristics of a Non-woven Polyester Geotextile with three different porosities (13.4, 19.5 and 26.0mum) but the same hydraulic conductivity (Kw = 10-5 m/s), when subjected to different heads of cattle slurry at 1, 2 and 4% total solids (TS) concentrations. The resulting infiltration rates were used to establish the effect of geotextile pore size and manure TS on geotextile sealing and to find the location of the seal, whether at the surface or within the geotextile. After 100 days of experimentation, the lowest infiltration rate of 1.1 L/m2/d was reached with the 13.4mum geotextile. Manure TS had a significant effect on the sealing and at least 4% TS was required to minimize the geotextile's infiltration rate. Clogging occurred within the pores, suggesting that the seal remains even after removing the manure. / This advantage can be translated into economic benefit when fun cost comparisons with sealing liners such as geomembranes and concrete are undertaken. / This research also reviews and analyzes the physical, chemical and biological processes leading to clogging of geotextiles as well as a cost-benefit comparison with the other sealing materials. The analysis concludes that clogged geotextiles are a wise choice for Canadian livestock producers.

This master thesis has been conducted through cooperation between Elforsk, Uppsala University and Tsinghua University in Beijing. Ashele Tailings Dam, located in Haba Town, Xianjing Province, China, is designed and used for high sulphur tailings. Because of a new mineral separation technique, the dam is now also being filled with low sulphur tailings. Since the dam was not originally designed for the new tailings materials, the seepage and stress-strain analyses of the dam need to be re-evaluated and refined. The Ashele Ltd. is also planning on building a new dam to meet its growing need for tailings deposit capacity. This dam will be used for the new low sulphur tailings and a thorough analysis of the dam will have to be performed.The purpose of this thesis is to re-evaluate the analyses of the seepage and stress-strain in the old dam and to perform the same type of analyses on the newdam. Numerical analyses of the seepage, solute transport and strain-stress in the dam are performed, using the physical and mechanical properties of the tailings materials. It is shown, that the construction of the new tailings dam, will have a good effect on the seepage and therefore also solute transport. The results also show that theseepage, solute transport, stress and deformation are depending on the amount ofwater in the tailings pond and that a lower water level has a positive effect on all thestudied variables.

Thesis (M.S. - Watershed Management)--University of Arizona. / Includes bibliographical references.

Thesis (Ph. D. - Watershed Management)--University of Arizona. / Includes bibliographical references (leaves 82-86).