The effects of air trapped in soils at zero or small negative values of matric potential were studied in relation to saturated and unsaturated hydraulic conductivity, the water release characteristic, and root growth. A reliable method was developed for measuring the trapped air porosity of 'saturated' soils. Using this method, the surface layer of three soils of contrasting texture, in a relatively undisturbed state, was found to have similar amounts of trapped air (5 to 7% of total soil volulme). After digging, the amount of air trapped by ponding water on the surface increased to a value of about 10%. Values of trapped air porosity below a stationary water-table were very low (1%) and this can be attributed to opportunity which the trapped air has to go into solution and diffuse to the water-table. The effects of trapped air on the water release characteristic were investigated in both field and laboratory studies using the neutron-probe and both the neutron-probe and the gamma-probe to measure the water content in the field soil and in a tank packed with sand in the laboratory, respectively. The presence of trapped air had an effect on the field water release characteristic. This effect was more pronounced in dug soil than in undisturbed soil. In the laboratory, the amount of trapped air differed according to the method of wetting, less trapped air occurred when wetting was from the bottom upwards compared to wetting by ponding water from the top. Amounts of trapped air decreased with increasing depth of sand. The water release characteristic was found to depend not only on the method of wetting but also on the previous history of wetting. In a comparison between a tension-table water release and the water release characteristic measured in a sand tank, they were found to be closely similar except at zero and small negative values of matric potential, where effects due to varying amounts of trapped air with depth and wetting history caused differences. Unsaturated hydraulic conductivity measured in the field was affected by the presence of trapped air but only at potentials close to zero. In the laboratory, the values of saturated hydraulic conductivity measured in the sand tank and the values calculated from the water release characteristic using Marshall's theory agreed to within the limits of experimental accuracy. Unsaturated hydraulic conductivity values were found to be not only dependent on the method of wetting but also on the previous history of wetting. The results suggested that once dry sand has been wetted and allowed to drain, that rewetting leads to trapping of air in large pores which reduces the flow during the next drainage period. There was an agreement between unsaturated hydraulic conductivity variation with matric potential obtained from the instantaneous profile method in the sand tank and that using Marshall's theory, however, it is not to be expected that such an agreement will be found for most soils which are not comparable to the relatively homogenous sand used here. In a laboratory experiment with winter barley, the relationship between the presence of trapped air, soil aeration and root growth was studied at 9 and 15°C. The techniques of measuring redox potential with bare platinum electrodes, measuring exygen flux with the same platinum electrodes, and measuring the concentrations of O₂, CO₂ and N₂O in samples extracted through a hypodermic needle gave results which were consistent with one another and with observed root growth rates. Root extension rate was much slower in the saturated soil than in the freely-drained soil. At both temperatures, root growth during 'daytime' (the time of illumination) was about 3 times greater than at night. At 15°C, there was a greater rate of root growth in soil cores which had been flooded rather than vacuum saturated which was related to a slightly greater measured rate of oxygen flux from air trapped by the flooding procedure.

An understanding of groundwater flow is essential in many aspects of mining. This is especially true for the sandstones of the Manitou Falls Formation, which overlie uranium deposits in the Athabasca Basin of northern Saskatchewan. Experience has shown that the hydraulic conductivities of these sandstones can be relatively high, especially in zones containing natural fractures, thus leading to potentially problematic groundwater inflow rates. This thesis presents the results of a study of hydraulic conductivity of the Manitou Falls Formation, in which detailed core logging and laboratory testing were undertaken for samples from two boreholes at the McArthur River mine site. Results from the logging and laboratory testing were interpreted in context provided by multiple packer tests conducted in these boreholes. Through core logging, indicators of conductive zones were identified. These indicators include fracture orientation (sub-vertical fractures were found to have more of an impact on conductivity than horizontal fractures), infilling, and staining. The laboratory testing program involved the measurement of hydraulic conductivities of fractured core samples across a span of effective confining pressures representative of in-situ conditions. Changes in fracture aperture were simultaneously recorded at each confining pressure level. It was found that theoretical relationships between aperture change and fracture conductivity represent the observed behavior of the samples reasonably well when fracture roughness is accounted for. The laboratory testing also confirmed the effects of fracture staining and infilling on hydraulic conductivity inferred from core logging and packer testing results. The results provide insights into the mechanisms underlying flow in fractured intervals of the Manitou Falls Formation, and provide guidance for selecting intervals to investigate during future packer testing in this formation.

The hydraulic conductivity of sand-bentonite mixtures (SBMs) was measured to investigate the effects of mixing method, uniformity, and hydration of the mixtures. Triaxial tests were completed to determine the hydraulic conductivity of each specimen. Specimens using Ottawa sand and Wyoming bentonite, prepared with dry and suspension mixing conditions that altered the degree of hydration and swelling of bentonite, had varying bentonite content by percentage dry weight of sand. The conclusions of this experiment can be applied to the construction of cut off walls used in levees to mitigate groundwater seepage through underlying pervious layers. Eleven sand-bentonite specimens were tested in this study: nine were prepared using dry mixing and two were prepared using suspension mixing. The results do not show strong correlations between hydraulic conductivity and bentonite content, mixing method, clay void ratio, or time. Therefore, further investigation of the results was necessary. The bentonite void ratio (clay void ratio) assumes that bentonite is fully swelled for both blocked and partially blocked flow. Blocked flow occurs when the swelled bentonite blocks all the sand voids, forcing the water to flow within the bentonite voids. However, the results in this study shows that the concept of clay void ratio doesn’t capture the performance of SBMs when the bentonite is partially swelled; therefore, a new concept of effective clay void ratio was introduced to account for bentonite partial swelling. The effective clay void ratio determines the volume of swelled clay as a function of the volume of fully swelled bentonite. This is useful when comparing results with literature or predicting hydraulic conductivity in cases where only partial swelling of bentonite is expected. / text

The objective of this project was to design a prototype field air permeameter that can be used to track changes in the hydraulic conductivity within soil covers with time. The evolution of soil structure in reclamation soil covers at the Syncrude Canada Ltd. oilsands mine is currently being studied. The Guelph permeameter is currently used to measure hydraulic conductivity, but gathering the data is a very time consuming task due to the relatively low hydraulic conductivity of the cover materials. The use of a faster, more efficient method would increase the capabilities for tracking changes in hydraulic conductivity of reclamation soil covers with time. <p>Three air permeameter design options were evaluated. One design was chosen and a prototype was built. Preliminary field trials were conducted at the Syncrude Canada Ltd. oilsands mine in August 2005. Air permeability measurements were taken on various soil cover treatments and slope positions. Improvements to the air permeameter were implemented in 2006, and additional data gathered. Guelph permeameter testing was carried out alongside the air permeameter in both field seasons. The air permeameter and Guelph permeameter were also tested under controlled laboratory conditions and compared to standard constant head column tests. <p>Results include correlations of air and water permeability for various materials and soil structures. Using dry uniform sand in a laboratory setting, the full scale air permeameter provided permeability values within 21% of a standard constant head column test. Testing of the air and Guelph permeameters on a cover constructed of peat-mineral mix over tailings sand revealed a difference of approximately one order of magnitude in permeability values. A difference of approximately two orders of magnitude existed between permeability values measured with the air and Guelph permeameters on till/secondary soil covers. <p>Further investigation into the difference between values of permeability measured with both methods is necessary. If successful, the air permeameter could prove to be a viable alternative to the Guelph permeameter for use in long-term monitoring of soil covers used in mine reclamation or waste containment. A more efficient air permeability method would allow a greater number of measurements to be made in a shorter time and could be used to track temporal as well as spatial variability in hydraulic conductivity.

The objective of this project was to design a prototype field air permeameter that can be used to track changes in the hydraulic conductivity within soil covers with time. The evolution of soil structure in reclamation soil covers at the Syncrude Canada Ltd. oilsands mine is currently being studied. The Guelph permeameter is currently used to measure hydraulic conductivity, but gathering the data is a very time consuming task due to the relatively low hydraulic conductivity of the cover materials. The use of a faster, more efficient method would increase the capabilities for tracking changes in hydraulic conductivity of reclamation soil covers with time. <p>Three air permeameter design options were evaluated. One design was chosen and a prototype was built. Preliminary field trials were conducted at the Syncrude Canada Ltd. oilsands mine in August 2005. Air permeability measurements were taken on various soil cover treatments and slope positions. Improvements to the air permeameter were implemented in 2006, and additional data gathered. Guelph permeameter testing was carried out alongside the air permeameter in both field seasons. The air permeameter and Guelph permeameter were also tested under controlled laboratory conditions and compared to standard constant head column tests. <p>Results include correlations of air and water permeability for various materials and soil structures. Using dry uniform sand in a laboratory setting, the full scale air permeameter provided permeability values within 21% of a standard constant head column test. Testing of the air and Guelph permeameters on a cover constructed of peat-mineral mix over tailings sand revealed a difference of approximately one order of magnitude in permeability values. A difference of approximately two orders of magnitude existed between permeability values measured with the air and Guelph permeameters on till/secondary soil covers. <p>Further investigation into the difference between values of permeability measured with both methods is necessary. If successful, the air permeameter could prove to be a viable alternative to the Guelph permeameter for use in long-term monitoring of soil covers used in mine reclamation or waste containment. A more efficient air permeability method would allow a greater number of measurements to be made in a shorter time and could be used to track temporal as well as spatial variability in hydraulic conductivity.

Orientador: Chang Hung Kiang / Banca: Everton de Oliveira / Banca: Gerson Cardoso da Silva Junior / Resumo: A Região Metropolitana de São Paulo apresenta áreas de embasamento cristalino alterado, densamente ocupadas, que sofreram os mais diversos impactos ambientais, comprometendo os aqüíferos presentes. Este trabalho teve por objetivo a caracterização da condutividade hidráulica da porção saturada de dois domínios hidrogeológicos do embasamento cristalino alterado, um relacionado às rochas metassedimentares e outro às rochas gnáissicas. A condutividade hidráulica de ambos os domínios foi determinada através da realização de testes de slug em 63 poços de monitoramento. Os testes foram realizados utilizando-se transdutor de pressão de alta precisão. Os dados obtidos foram armazenados e analisados, utilizando-se os métodos de Hvorslev (1951) e Bower & Rice (1976). Os valores de condutividade hidráulica de cada domínio hidrogeológico, obtidos por ambos métodos, foram comparados através de análises estatísticas. Procurou-se estabelecer a relação entre os valores de condutividade hidráulica e a profundidade do meio saturado, bem como a influência das heterogeneidades presentes nos dois domínios hidrogeológicos. Os resultados dos testes revelaram que a condutividade hidráulica média das rochas gnáissicas alteradas é de 7,51x10-4 cm/s, segundo o método de Hvorslev (1951), e 2,34 x10-3 cm/s para o método de Bouwer & Rice (1976). Para as rochas metassedimentares alteradas foram obtidos valores médios de 5,01x10-5 cm/s e 7,99x10-5 cm/s, respectivamente. / Abstract: The São Paulo Metropolitan Region (RMSP) is located on crystalline rock areas. The region is highly populated and has suffered different environmental impacts, affecting the aquifers. The objective of this work is to characterize the of the satured portion of two different hydrogeological domains, consisting of weathered basement, one related to the metassedimentary rocks and another to gneissic rocks. The hydraulic conductivities of both domains were determined by a series of slug tests in 63 monitoring wells. The tests were executed using a high precision pressure transducer. The data from the tests were collected, stored and analyzed using new analytical tools based on Hvorslev (1951) and Bower and Rice (1976) methods. The conductivity values obtained from both methods were evaluated using statistical analysis, looking for relationships among hydraulic conductivity, depth of satured zone, as well as heterogeneity present on both hydrogeologic domains. Hydraulic conductivity values for weathered gneiss were 7,51x10-4 cm/s and 2,34 x10-3 cm/s obtained using Hvorslev (1951) and Bower and Rice (1976), respectively. For metassedimentary rocks hydraulic conductivity values were 5,01x10-5 cm/s and 7,99x10-5 cm/s, respectively. / Mestre

[pt] presente dissertação descreve o desenvolvimento de um equipamento destinado a determinar a condutividade hidráulica de meios porosos saturados in situ. O permeâmetro consiste em uma sonda que emprega o método da vazão constante. Após sua inserção pelo modo de cravação. Uma bomba de seringa instalada na superfície do terreno é utilizada para aplicar uma vazão constante enquanto que a carga hidráulica induzida no meio é medida através de um transdutor de pressão piezoresistivo instalado no corpo da sonda. O equipamento permite o escoamento das linhas de drenagem e de medição de carga hidráulica a partir da superfície possibilitando a saturação do meio poroso após a cravação da sonda bem como minimiza as incertezas associadas à medição de pressão. Esta última é alcançada através de um transdutor diferencial de pressão com uma faixa de trabalho de 10kPa que possibilita medições de poropressões bem próximas a zona de injeção. Esta característica permite a realização de ensaios num tempo curto e minimiza o problema de compatibilidade de fluidos decorrente do processo de injeção. / [en] This thesis describes a piece of equipment developed to determine the hydraulic conductivity of saturated porous media. The permeameter consists of a pushed in probe and employs the constant flow rate method. A syringe pump installed on the surface is used to develop a constant rate of flow whereas a piezoelectric transducer installed in the probes body measures the induced change in hydraulic head. The great innovation in this device consists on its ability of saturating all of its drainage lines allowing the media to be saturated and minimizing the errors of pressure measurements. Pressure measurement is carried out using a 10kPa differential pressure transducer that enables porepressure to be measured close to the injection zone. This characteristic enables shorter tests to be carried out and minimize problems associated to fluid compability

Thesis advisor: Alfredo Urzua / Thesis advisor: John Ebel / Nine empirical equations that estimate saturated hydraulic conductivity as a func- tion of grain size in well-graded sands with gravels having large uniformity coecients (U > 50) are evaluated by comparing their accuracy when predicting observed conduc- tivities in constant head permeability tests. According to the ndings of this thesis, in decreasing order of accuracy these equations are: USBR (Vukovic and Soro, 1992; USBR, 1978), Hazen (Hazen, 1892), Slichter (Slichter, 1898), Kozeny-Carman (Carrier, 2003), Fair and Hatch (Fair and Hatch, 1933), Terzaghi (Vukovic and Soro, 1992), Beyer (Beyer, 1966), Kruger (Vukovic and Soro, 1992), and Zunker (Zunker, 1932). These re- sults are based on multiple constant head permeability tests on two samples of granular material corresponding to well-graded sands with gravels. Using the USBR equation sat- urated hydraulic conductivities for a statistical population of 874 samples of well-graded sands with gravels forming 29 loads from a heap leaching mine in northern Chile are calculated. Results indicate that, using the USBR equation, on average the hydraulic conductivity of the leaching heaps has a two standard deviation range between 0.18 and 0.15 cm/s. Permeability tests on the actual material used in the heaps provided by the mine shows that the results presented in this thesis are consistent with actual observa- tions and represent saturated conductivities in heaps up to 3 m high under a pressures of up to 62 Kpa. In future work hydraulic conductivities can be combined with water retention curves, discharge rates, irrigation rates, porosities, and consolidation so as to evaluate the relationship between copper yields and the hydraulic conductivities of the heap. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Soil-bentonite (SB) slurry walls are one of the most popular techniques for minimizing the horizontal migration of contaminants. Backfill arching, or “hang-up” of the backfilled slurry, on the wall trench has the potential to significantly reduce the effectiveness of these barriers. This research was conducted to supplement the design and installation of an 11,000 m long slurry wall at PotashCorp’s mine in Rocanville, Saskatchewan. The slurry wall is being installed through low permeability glacial till containing permeable granular zones. This study was undertaken to improve the understanding of vertical stress distribution in these deep barriers. In particular, the objective of this study was to develop an understanding of the factors controlling arching and hydraulic conductivity (k) of SB walls. Slurry wall “hang-up” or arching is dependent on shear along the wall of the trench and on a coefficient of lateral earth pressure (K). Consolidated drained (CD) shear box tests were conducted to study the shear strength parameters of the backfill mixes. Six inch proctor mold was modified with load cells on the side walls to measure horizontal stresses along with consolidation. This was used to calculate coefficient of lateral earth pressure, K (which is the ratio of horizontal to vertical effective stress). The results of the laboratory testing program found that K was relatively independent of the percentage of fines present in the SB mix. It also showed that backfill angle of internal friction and k of the backfill decreased with increased fines content. The results of the laboratory testing program were used to model the vertical stress distribution in deep walls. An analytical model (discrete model) and a coupled seepage stress-strain finite element model (FEM) were used to predict vertical stress changes with time and depth for the different backfill materials. The primary conclusion of this research is that slurry wall backfill arching or “hang-up” significantly delays the magnitude and timing of vertical stress build-up in backfill. This loss of vertical stress results in backfill with lower density and higher hydraulic conductivity. The situation was found to be most critical for deep narrow slurry walls. Any advantage in using a coarser graded backfill was offset by higher backfill hydraulic conductivity. The net result is that the upper portions of slurry walls may not be able to achieve their hydraulic conductivity objectives as soon as expected, if at all. In addition, the backfill in the upper portion of the trench may be susceptible to chemical attack and osmotic consolidation. Construction of a 2 m high surcharge berm over the slurry wall was found to increase vertical effective stress and result in significantly lower (2 to 8 times) hydraulic conductivity values in the top 5 metres of the trench. The final hydraulic conductivity (k) at a depth of 5 m was approximately 75 % lower with a surcharge berm. Thus, construction of a surcharge berm over the slurry wall helps to satisfy the k requirement for SB walls and lowers the risk of osmotic consolidation.

Artificial drainage networks established throughout peatlands during the peat extraction process often remain active following abandonment, maintaining a water table relatively far from the surface of the peat and hindering the survival and reestablishment of Sphagnum mosses. Since cutover peatlands are characterized by low (negative) soil water pressures, sufficient internal water storage and balanced water fluxes are critical for the physiological function of spontaneously regenerated Sphagnum mosses. The relative importance of water exchanges between spontaneously regenerated Sphagnum moss cushions and their surroundings are addressed through investigation of the sensitivity of moss moisture dynamics to a range of environmental variables. Precipitation waters are poorly retained within the cushions, which indicated that rain event water can only be relied upon by the mosses for a short period of time. An imbalance between water inputs and losses from moss cushions identified that additional (small) sources of water, such as dewfall and distillation, are potentially important for physiological processes under dry conditions, common in disturbed peatland ecosystems. As an initial restoration effort, rewetting of the peatland by blocking drainage ditches consequently reduced the runoff efficiency and caused the site-average water table to rise by 32 cm. Higher water tables and a blocked drainage network created conditions more favourable for Sphagnum survival through increasing the moisture content and soil-water pressures within the remnant peat deposit. The hydrologic connectivity between moss cushions and the remnant peat was strong when conditions were wet and the water table was within 30 cm of the surface of the cutover peat but weakened as conditions became drier, as reflected by weakened upward hydraulic gradients in the unsaturated zone below the moss cushions. Runoff variability increased following rewetting, and displayed a greater dependence upon antecedent conditions (capacity to retain additional water on-site) and event-based precipitation dynamics. Evapotranspiration rates were 25% higher following rewetting (3.6 mm day-1) compared to pre-restoration ET rates of 2.7 mm day-1. Total storage changes were restricted following rewetting, as a factor of the reduced runoff losses limiting water table drawdown, thereby constraining peat compression and preventing undue drying of the unsaturated zone. Changes to the system hydrology following rewetting of the peatland by blocking drainage ditches created conditions more favourable for Sphagnum survival through increasing the moisture content and soil-water pressures within the remnant peat deposit; although restoration efforts should aim to constrain water table fluctuations to within the upper 30 cm.