Intercommunication has been identified between the unconfined and uppermost confined aquifer systems underlying a portion of the U.S. Department of Energy's Hanford Site. Erosional thinning and fracturing of the basalt confining layer within the study area allows physical contact between the two aquifers, but the vertical hydraulic gradient (a required driving force) is small. To better conceptualize the distribution and volume of the leakage occurring between the aquifer systems, this study investigates the confined Rattlesnake Ridge Aquifer flow system, which appears to be more sensitive to the vertical leakage than the overlying unconfined aquifer.

Estuarine ecosystems are under enormous stress due to rapid coastal developments and climate change. Proper management of these important ecosystems requires a good understanding of their key processes. In this thesis, riparian groundwater-surface water interaction is explored for an aquifer-estuary system primarily by a series of numerical experiments. The work focuses on riparian-scale groundwater flow and salinization. The overall aim of the study was to extend our understanding of aquifer-estuary exchange, which is currently centered on the lower marine estuarine reach, to middle estuaries (i.e., the estuary reach that has variable salinity). The numerical experiments were guided by previous studies and observations made from an exploratory field investigation conducted in and next to Sandy Creek, a macro-tidal estuary incised in the alluvial aquifer of the Pioneer Valley, North-eastern Australia (Longitude 49.11°, Latitude -21.27°). The following observations were made from the field investigation: Sandy Creek estuary experiences a variable salinity regime in its mid reaches that consists of periods of 1) freshwater flushing due to up catchment-derived flooding, 2) persistent freshwater conditions for at least 2 months following the flooding, 3) tidal salinity fluctuations and 4) constant near-seawater salinity; laterally extensive and disconnected aquitards were found to occur at the field site; Sandy Creek had an essentially ‘vertical’ bank slope. Numerical simulations were conducted using the finite element modeling code FEFLOW for saturated unsaturated, variable-density groundwater flow and solute transport, to examine the influence of the following factors on aquifer-estuary exchange: a tidally varying estuarine salinity and hydraulic head, a seasonal freshwater flush (i.e., estuary with freshwater and an elevated stage due to an up catchment sourced flood), near estuary aquitard layers, lateral asymmetry (about the estuary centerline) in hydraulic conductivity and regional hydraulic gradients. The simulations neglected seepage face development after numerical experiments showed that for a vertical bank estuary interacting with a sandy loam aquifer, seepage face effects on groundwater flow and associated salinity distribution were minimal. The following observations were drawn from the range of numerical experiments considered. Tidal salinity fluctuations in the estuary (varying between 0 and 1 - i.e., using a relative salinity scale where a salinity of 1 is seawater) produced flow paths and residence times that were distinctly different to the constant seawater salinity case. While the constant average 0.5 salinity case and the corresponding tidally-varying salinity case (i.e., salinity varying between 0 and 1) produced somewhat comparable results in terms of RUC and RLC (RUC represents groundwater discharge to the estuary that originated from recharge to the estuary bank and RLC groundwater discharge to the estuary that originated from recharge through the estuary bed), whereas flow paths and the total salt mass in the aquifer differed. Freshwater flushing simulations indicated that the near-estuary aquifer responds rapidly to a 2-day ‘wet season’ flushing event with a short-lived freshwater lens created through freshening of the hyporheic zone. Annual cycling of the seasonal flushing led to significant disruption of the estuary water circulation in the aquifer thereby impacting on residence times, transport pathways, and RUC and RLC, and acting to potentially remobilize groundwater and contaminants previously trapped in continuous and semi-continuous re-circulation cells. Although groundwater flow paths determined using tide-averaged velocity vectors were representative of flow paths from transient tidally driven flow vector field, residence times calculated from the two flow fields were markedly different. The influence of riparian scale aquitards and lateral asymmetry (about the estuary centreline) in hydraulic gradients and hydraulic conductivity on groundwater flow and associated salinity distribution was also found to be sensitive to estuarine salinity conditions. The results indicate that observations made about aquifer-estuary interaction in the lower estuary may not be directly applicable to the middle estuary. According to the simulations, tidal salinity variations in the estuary are important factors that affect hyporheic-riparian salt transport processes and that the use of a time averaged estuarine salinity as an approximation to variable salinity conditions is unsuitable for the accurate prediction of the near-estuary dynamics in middle estuaries. This study was based on a two dimensional representation of the riparian scale interaction and it is clear that future research needs to focus on the three-dimensionality of the aquifer-estuary system, incorporating spatially and temporally varying flow and transport characteristics. That is, many estuaries are tortuous and the aquifer geology spatially complex such that assumptions required for the two-dimensional section will most likely restrict application to the field. The tidal dynamics in the middle estuary is also expected to generate three dimensional aspects to the aquifer-estuary interaction. Thus further investigation that explicitly models the hydrodynamics and salt transport in the estuary and estuarine morphology is required to refine the insight provided by the simple conceptual model adopted in this study.

La thèse a pour objet la simulation numérique de divers problèmes fortement non linéaires de la mécanique des milieux continus, en particulier en formage des métaux et en géomécanique. Le formalisme théorique puis numérique de la mécanique non linéaire des milieux continus, des couplages hydromécaniques et thermomécaniques et des modèles de comportement élastoplastique et élastoviscoplastique est développé étape par étape, permettant la construction du code aux éléments finis LAGAMINE. Celui-ci est ensuite utilisé pour simuler quelques problèmes spécifiques.

In this thesis, the mechanism of landslides in loess slope is studied based on a field test in association with laboratory tests and numerical modeling. The field test was carried out in the Heifangtai Plateau in China. Heifangtai belongs to semiarid monsoonal with scarce precipitation. Therefore, agricultural irrigation is the major source of water infiltration for the loess slopes in Heifangtai. The test site was selected at the crest of a steep loess slope with developed cracks, covered by more than 40m loess layer. Ground investigation, including lithological composition, groundwater level, soil sampling and soil permeability, was conducted. A field monitoring program was then performed by installation of inclinometers, piezometers, moisture probes, tensiometers and crackmeters. The field irrigation test with instrument monitoring was conducted at the test site on October 2009, lasting for 12 days. Based on field observation and monitoring results, some typical failures occurred in the field test were analyzed in details, including development of cracks, formation of sinkholes and failures on slope surface. These failures are representative in loess regions and are potential factors of loess landslides. A conceptual model was proposed to reflect soil failures induced by water infiltration along the crack. To characterize the loess behavior to infiltration, a comprehensive triaxial testing program was conducted on trimmed loess specimens sampled in Heifangtai. The fundamental behavior of loess was investigated following different stress paths under both saturated and unsaturated conditions. Based on triaxial tests, the soil parameters including mechanical properties and hydraulic properties were obtained. The finite difference program FLAC3D was adopted in this study, the fluid model of which was extended from saturated flow to saturated/unsaturated flow. A numerical model was built to study the mechanism of soil failures induced by variation of water level in the crack, using a proposed moving boundary algorithm. In the numerical modeling, fluid-mechanical coupled analysis was conducted by solving Biot’s consolidation equation, utilizing soil parameters obtained in the laboratory tests. The proposed conceptual model in the field test was verified in the numerical analysis. Subsequently, different draining rates of water in the crack were simulated to investigate soil failures affected by the dropping of water level in the crack. Based on the numerical analysis, the mechanism of sinkhole formation was discussed. Finally, conclusions and recommendations for future research on loess landslides induced by infiltration were made. It is hoped that the study on the mechanism of loess landslides can provide a useful reference for the future research. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

Deep interceptor drains are commonly used to control canal seepage in southern Alberta, Canada. Recently, shallow grid drainage was introduced. A study was initiated in 1987 to assess the effectiveness of grid drainage to intercept canal and natural groundwater seepage and reclaim the resulting saline affected land. / Using a groundwater flow model, MODFLOW, it was found that a single deep interceptor drain would have failed to intercept all canal seepage and maintain the water table downslope of the canal below the 1.0 m design water table depth. Conversely, simulations indicated that with a grid drainage system, all canal and natural groundwater seepage would be intercepted and the water table would remain below the design water table depth, with or without irrigation recharge that would maintain a steady state salt balance. / The benefits of fall irrigation were demonstrated using three test plots near the canal.

In the past decade, the grouting industry has made significant technological advancements in real-time monitoring of flow rate and pressure of pumped grout, stable grout mix design, and with grout curtain concepts dealing with placement and orientation. While these practices have resulted in improved construction practices in the grouting industry, current design guidelines for grout curtains are still predominately based on qualitative measures such as engineering judgment and experience or are based on proprietary methods. This research focused on the development of quantitative guidelines to evaluate the effectiveness of a grout curtain in porous media using piezometric and hydraulic flow data. In this study, a laboratory-scale physical seepage model was developed to aid in the understanding and development methodology to evaluate the effectiveness of a grout curtain. A new performance parameter was developed based on a normalization scheme that utilized the area of the grout curtain and the area of the improved media. The normalization scheme combined with model-based Lugeon values that correspond to pore pressure and flow rate measurements at different soil unit weights and grout curtain spacings, produced a mathematical equation that can be used to quantify the effectiveness of a grout curtain. This study found a relationship that takes into account soil unit weight, grout curtain spacing and a new performance parameter that can be used to help predict the effectiveness of a grout curtain.

In humid environments surface water erosion, rather than seepage water erosion has been considered the major erosional force. The canyons in Starved Rock State Park, north-central Illinois, are not typical in form for eastern United States humid-temperate climate landscapes. In and around Starved Rock State Park the valley cross-profiles are box shaped rather than "V"-shaped with amphitheater heads, steep walls and broad valley bottoms. Other large and small-scale features of the canyons are also largely indicative of seepage erosion.Using field data it was determined that active canyon headwall erosion was occurring in the park at a rate of approximately 0.02 m/year. This is in fact the rate that would be needed to erode the canyons to their current length, showing that seepage erosion, the dominant erosional force in the park, is indeed capable of erosion rates necessary to entirely form the canyons within Starved Rock State Park. / Department of Geology

Between 2004 and early 2006 a large-scale, instrumented, potentially contaminating trial waste rock dump was constructed and monitored at Cadia Hill Mine, in NSW, Australia. The trial waste rock dump was instrumented with lysimeters to measure rainfall infiltration and seepage through its base, and temperature sensors and gas sampling tubes to evaluate oxidation of the waste rock, together with three instrumented trial store and release covers on the surface. This thesis describes the construction and instrumentation of the trial waste rock dump and the monitoring results obtained to date, and applies unsaturated soil mechanics principles to understanding the early performance and predicting the future performance of the trial waste rock dump and trial store and release covers. For a given rainfall regime, the rate and quantity of rainfall infiltration into a waste rock dump of a given height, the wetting up of the dump over time, and the occurrence of base seepage will largely be dictated by the particle size distribution of the waste rock delivered to the dump, and the stratigraphy of the dump. The particle size distribution of the waste rock delivered to the dump will depend on the fragmentation of the rock due to blasting and the degree of weathering and hence breakdown on handling of the rock. A waste rock dump constructed by conventional loose end-dumping from haul trucks from a tip-head, as was the case for the trial waste rock dump, consists of a trafficked surface layer extending to a depth of approximately 1 m, underlain by discontinuous alternating coarse and fine-grained layers raveling at the angle of repose of the waste rock, with a base rubble zone of boulders which ravel to the toe of the dump on end-dumping. Trafficking of the surface of the dump by dozers and haul trucks leads to the breaking down, burial and side-casting of the rock to form a well-graded material typically finer than 100 mm in particle size, with a moderate to high water storage capacity. The underlying coarse-grained angle of repose layers serve as air pathways during dry conditions and preferred seepage pathways during and following periods of heavy rainfall resulting in base seepage. The fine-grained angle of repose layers have a moderate to high water storage capacity and largely retain water in storage rather than generating base seepage. The base rubble zone may contain boulders up to 1 m in size, depending on the fragmentation of the rock due to blasting and the degree of weathering and hence breakdown on handling of the rock. It serves largely as a pathway for air during dry conditions, while passing base seepage during and following periods of heavy rainfall. As the dump wets up, partially saturated “fingers” develop and extend into the dump. Partially saturated fine-grained layers, having a medium to high water storage capacity, largely retain their partial saturation, while coarse-grained layers drain resulting, in base seepage. Plugs of water temporarily stored within the dump drain down through the dump, so that the base seepage that emerges is “old” water, not the rainfall infiltration (“new” water) that generated it. The size of the rainfall event required to generate base seepage will decrease as the dump wets up and the partially saturated fingers extend closer to the base of the dump. The residence time of water within the dump that passes along preferred seepage pathways will be relatively short and will become shorter as the dump wets up, while the residence time of water stored within the fine-grained layers will be very long, and possibly indefinite in a dry climate. The ingress of air through the base rubble zone, up the coarse-grained angle of repose layers, through the sides of the dump, and to a lesser extent through the trafficked layer, by the processes of convection, advection and diffusion, respectively, results in the exposure of reactive waste rock to oxidation. The fine-grained reactive waste rock, presenting a far greater surface area per unit volume than the coarse-grained waste rock, and typically having a greater proportion of fresh surfaces, is by far the most reactive. The ingress of air into the fine-grained layers is largely by diffusion from the adjacent coarse-grained layers. The transport of oxidation products from the dump largely occurs during and following periods of heavy rainfall, when preferred pathway flow is mobilised and base seepage occurs. The main exposure to preferred pathway flow is along these pathways, where the surface area per unit volume and hence the proportion of oxidation products are low, with much of the oxidation products formed on the fine-grained particles retained within the dump along with stored water. Due to the discontinuous stratigraphy of a waste rock dump, the preferential pathways for flow are randomly located within the dump. In addition, preferential pathways evolve over time as the waste rock weathers, settles, and as fines are transported with the flow. The trafficked surface of the dump also evolves over time, becoming more heterogeneous as the surface settles differentially, generating internal rainfall runoff and the transport of fines, and the development of “sinkholes” for the preferred entry of ponded rainfall. The principle purpose of cover systems over waste rock dumps is to restrict net percolation into the dump, so that percolation through the reactive waste rock is minimal in the longer term. The approach used to design any cover system is dominated by climate. Semi-arid environments are conducive to store and release cover systems which take advantage of well-graded oxide materials to provide high storage capacities, low percolation and stability. Three trial store and release covers, each comprising a sealing layer overlain by a thick mounded rocky soil mulch layer, were installed at Cadia Hill Mine in 2005-2006 to assess their feasibility to limit net percolation under the climatic conditions encountered at Cadia. This research described in this thesis has demonstrated a number of key issues that should be considered in the management and closure of waste rock dumps: • the initial moisture condition of the end-dumped waste rock will effect its early ability to store incidental rainfall; • the available water storage capacity of the waste rock will affect the size of the triggering rainfall event and the base seepage response time, with the storage capacity being taken up as the dump wets up, reducing both the size of the triggering rainfall event and the response time; • iterative modelling and calculations using HYDRUS-2D suggest that the trial waste rock dump will take between 3 years and 6 years to become sufficiently saturated that it will pass any rainfall infiltration, depending on the extent to which the waste rock weathers over time; and • all three trial store and release covers have demonstrated good performance over the monitoring period, and this has been verified using HYDRUS-2D, , with any net percolation being the result of an initial high placement moisture content of the cover materials.

Estuarine ecosystems are under enormous stress due to rapid coastal developments and climate change. Proper management of these important ecosystems requires a good understanding of their key processes. In this thesis, riparian groundwater-surface water interaction is explored for an aquifer-estuary system primarily by a series of numerical experiments. The work focuses on riparian-scale groundwater flow and salinization. The overall aim of the study was to extend our understanding of aquifer-estuary exchange, which is currently centered on the lower marine estuarine reach, to middle estuaries (i.e., the estuary reach that has variable salinity). The numerical experiments were guided by previous studies and observations made from an exploratory field investigation conducted in and next to Sandy Creek, a macro-tidal estuary incised in the alluvial aquifer of the Pioneer Valley, North-eastern Australia (Longitude 49.11°, Latitude -21.27°). The following observations were made from the field investigation: Sandy Creek estuary experiences a variable salinity regime in its mid reaches that consists of periods of 1) freshwater flushing due to up catchment-derived flooding, 2) persistent freshwater conditions for at least 2 months following the flooding, 3) tidal salinity fluctuations and 4) constant near-seawater salinity; laterally extensive and disconnected aquitards were found to occur at the field site; Sandy Creek had an essentially ‘vertical’ bank slope. Numerical simulations were conducted using the finite element modeling code FEFLOW for saturated unsaturated, variable-density groundwater flow and solute transport, to examine the influence of the following factors on aquifer-estuary exchange: a tidally varying estuarine salinity and hydraulic head, a seasonal freshwater flush (i.e., estuary with freshwater and an elevated stage due to an up catchment sourced flood), near estuary aquitard layers, lateral asymmetry (about the estuary centerline) in hydraulic conductivity and regional hydraulic gradients. The simulations neglected seepage face development after numerical experiments showed that for a vertical bank estuary interacting with a sandy loam aquifer, seepage face effects on groundwater flow and associated salinity distribution were minimal. The following observations were drawn from the range of numerical experiments considered. Tidal salinity fluctuations in the estuary (varying between 0 and 1 - i.e., using a relative salinity scale where a salinity of 1 is seawater) produced flow paths and residence times that were distinctly different to the constant seawater salinity case. While the constant average 0.5 salinity case and the corresponding tidally-varying salinity case (i.e., salinity varying between 0 and 1) produced somewhat comparable results in terms of RUC and RLC (RUC represents groundwater discharge to the estuary that originated from recharge to the estuary bank and RLC groundwater discharge to the estuary that originated from recharge through the estuary bed), whereas flow paths and the total salt mass in the aquifer differed. Freshwater flushing simulations indicated that the near-estuary aquifer responds rapidly to a 2-day ‘wet season’ flushing event with a short-lived freshwater lens created through freshening of the hyporheic zone. Annual cycling of the seasonal flushing led to significant disruption of the estuary water circulation in the aquifer thereby impacting on residence times, transport pathways, and RUC and RLC, and acting to potentially remobilize groundwater and contaminants previously trapped in continuous and semi-continuous re-circulation cells. Although groundwater flow paths determined using tide-averaged velocity vectors were representative of flow paths from transient tidally driven flow vector field, residence times calculated from the two flow fields were markedly different. The influence of riparian scale aquitards and lateral asymmetry (about the estuary centreline) in hydraulic gradients and hydraulic conductivity on groundwater flow and associated salinity distribution was also found to be sensitive to estuarine salinity conditions. The results indicate that observations made about aquifer-estuary interaction in the lower estuary may not be directly applicable to the middle estuary. According to the simulations, tidal salinity variations in the estuary are important factors that affect hyporheic-riparian salt transport processes and that the use of a time averaged estuarine salinity as an approximation to variable salinity conditions is unsuitable for the accurate prediction of the near-estuary dynamics in middle estuaries. This study was based on a two dimensional representation of the riparian scale interaction and it is clear that future research needs to focus on the three-dimensionality of the aquifer-estuary system, incorporating spatially and temporally varying flow and transport characteristics. That is, many estuaries are tortuous and the aquifer geology spatially complex such that assumptions required for the two-dimensional section will most likely restrict application to the field. The tidal dynamics in the middle estuary is also expected to generate three dimensional aspects to the aquifer-estuary interaction. Thus further investigation that explicitly models the hydrodynamics and salt transport in the estuary and estuarine morphology is required to refine the insight provided by the simple conceptual model adopted in this study.