Over fifty small sinkholes (~1 meter in depth and width) were found in conjunction with structural damage to homes in an area south of Cleveland, TX. The local geology lacks carbonate and evaporite deposits associated with normal sinkhole development through dissolution. The morphology and distribution of sinkholes, and the geologic setting of the site are consistent with piping erosion. However, the site lacked the significant hydraulic gradient or exit points for sediment associated with traditional piping erosion. In areas of sinkholes, geophysical measurements of apparent electrical conductivity delineated anomalously high conductivity levels that are interpreted as a brine release from a nearby oil-field waste injection well. The contaminated areas have sodium adsorption ratios (SAR) as high as 19, compared to background levels of 3. Sodium has been shown to cause dispersion of soil colloids, allowing for sediment transport at very low velocities. Thus, subsurface erosion of dispersed sediment could be possible without significant hydraulic gradients. This hypothesis is backed by the observation of the depletion of colloidal particles within the E-horizon of sinkholes. However, there is a lack of precedence of waste brines initiating colloid dispersion. Also, sodium dispersion is not thought to be an important process in piping erosion in humid settings such as this one. Therefore, laboratory experiments on samples from the site area, designed to simulate field conditions, were conducted to measure dispersion verses pH, SAR and electrical conductivity (EC). Analysis of the experimental data with neural networks showed that an increase in SAR did increase dispersion. A dispersion prediction map, constructed with the trained neural network and calibrated geophysical data, showed correlation between sinkhole locations and increased predicted dispersion. This research indicates that a contaminant high in sodium content has caused colloidal dispersion, which may have allowed nontraditional subsurface erosion to occur in an area lacking a significant hydraulic gradient.

Over fifty small sinkholes (~1 meter in depth and width) were found in conjunction with structural damage to homes in an area south of Cleveland, TX. The local geology lacks carbonate and evaporite deposits associated with normal sinkhole development through dissolution. The morphology and distribution of sinkholes, and the geologic setting of the site are consistent with piping erosion. However, the site lacked the significant hydraulic gradient or exit points for sediment associated with traditional piping erosion. In areas of sinkholes, geophysical measurements of apparent electrical conductivity delineated anomalously high conductivity levels that are interpreted as a brine release from a nearby oil-field waste injection well. The contaminated areas have sodium adsorption ratios (SAR) as high as 19, compared to background levels of 3. Sodium has been shown to cause dispersion of soil colloids, allowing for sediment transport at very low velocities. Thus, subsurface erosion of dispersed sediment could be possible without significant hydraulic gradients. This hypothesis is backed by the observation of the depletion of colloidal particles within the E-horizon of sinkholes. However, there is a lack of precedence of waste brines initiating colloid dispersion. Also, sodium dispersion is not thought to be an important process in piping erosion in humid settings such as this one. Therefore, laboratory experiments on samples from the site area, designed to simulate field conditions, were conducted to measure dispersion verses pH, SAR and electrical conductivity (EC). Analysis of the experimental data with neural networks showed that an increase in SAR did increase dispersion. A dispersion prediction map, constructed with the trained neural network and calibrated geophysical data, showed correlation between sinkhole locations and increased predicted dispersion. This research indicates that a contaminant high in sodium content has caused colloidal dispersion, which may have allowed nontraditional subsurface erosion to occur in an area lacking a significant hydraulic gradient.

In September 2008 Hurricane Ike hit the Texas Gulf Coast with a force stronger than the category 2 storm at which it was rated. With a 3.8 m (12.5 ft) storm surge, the agricultural industry in the area was devastated. The goal of this research was to determine the length of time required to reduce the salt levels brought by the storm surge to near pre-hurricane levels. To do this, four sets of samples were taken across two years and analyzed for salinity using the saturated paste extract method. The initial salt levels in November 2008 had an electrical conductivity (ECe) of the inundated soils as high as 26.7 dS/m. Fifty-four percent of the soils sampled in the 0-15 cm horizons and 9% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 79% of the soils sampled in the 0-15 cm horizons and 30% in the 15-30 cm horizons had an ECe >= 4 dS/m. In April 2009, 38% of the soils sampled in the 0-15 cm horizons and 13% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 71% of the soils sampled in the 0-15 cm horizons and 39% in the 15-30 cm horizons had an ECe >= 4 dS/m. By December 2009, none of the soils sampled in the edge area had an ECe >= 4 dS/m. In the surge area 21% of the soils sampled in the 0-15 cm horizons and 33% in the 15-30 cm horizons had an ECe >= 4 dS/m. By October 2010, all soils sampled had leached sufficient salts to be classified as non-saline to very slightly saline soils. Utilizing the November 2008 data set, 28 random samples were selected for exchangeable Na percent (ESP) in order to develop the ESP-SAR (Na adsorption ratio) predictive equation, ESP= 1.19(SAR)^0.82. The SAR-ESP relationship is statistically significant (95% confidence level), with a correlation coefficient of 0.964 (df=26).

[Truncated abstract] Self-filtration is here defined as particle detachment and re-deposition causing re-arrangement of the particles and therefore pore space which affects water flow in soil by decreasing hydraulic conductivity. This is of particular important in soils which are susceptible to structural breakdown. The objective of this thesis was to examine the dynamics of the self-filtration process in sodic sandy soils as affected by ionic strength and soil solution composition. The temporal changes of hydraulic conductivity and the elution of fine particles from soil columns were used as the main criteria to assess selffiltration. Two porous media exhibiting significantly different structural cohesion were examined, one a loamy sand (Balkuling soil) from agricultural land use and the second a mining residue from mineral sands operations . . . The effects of the composition of mixed calcium (Ca) and sodium (Na) ions in solution (sodium adsorption ratio (SAR)) on the exchange behaviour and saturated hydraulic conductivity were examined by carrying out batch binary exchange and saturated column transport experiments. A strong preference for Ca2+ ions in the exchange complex was observed for both soils. Generally K/Ko was found to decrease with increasing sodium adsorption ratio with the more structured Balkuling soil maintaining K/Ko for SARs 3 and 5 at an electrolyte concentration of 100 mmol/L. However measurements at the critical threshold and turbidity concentrations at a SAR of 15 revealed structural breakdown of the pore matrix system attributed to various extents of slaking, swelling, dispersion and decreases of pore radii as a result of selffiltration during leaching. These experiments illustrate the wide range of complex interactions involving clay mineralogy, solution composition and structural factors which can influence the extent of mobilization, transport and re-deposition of colloidal particles during the leaching process in soil profiles.

A study was conducted to evaluate the properties and processes influencing the rate and magnitude of volume decrease and strength gain for oil sand fine tailings resulting from a change in bitumen extraction process (caustic versus non-caustic) and the effect of adding a coagulant to caustic fine tailings. Laboratory flume deposition tests were carried out with the objective to hydraulically deposit oil sand tailings and compare the effects of extraction processes on the nature of beach deposits in terms of geometry, particle size distribution, and density. A good correlation exists between flume deposition tests results using oil sand tailings and the various other tailings materials. These comparisons show the reliability and effectiveness of flume deposition tests in terms of establishing general relationships and can serve as a guide to predict beach slopes. Fine tailings were collected from the various flume tests and a comprehensive description of physical and chemical characteristics of the different fine tailings was carried out. The characteristics of the fine tailings is presented in terms of index properties, mineralogy, specific surface area, water chemistry, liquid limits, particle size distribution and structure. The influence of these fundamental properties on the compressibility, hydraulic conductivity and shear strength properties of the fine tailings was assessed. Fourteen two meter and one meter high standpipe tests were instrumented to monitor the rate and magnitude of self-weight consolidation of the different fine tailings materials. Consolidation tests using slurry consolidometers were carried out to determine consolidation properties, namely compressibility and hydraulic conductivity, as well as the effect of adding a coagulant (calcium sulphate [CaSO4]) to caustic fine tailings. The thixotropic strength of the fine tailings was examined by measuring shear strength over time using a vane shear apparatus. A difference in water chemistry during bitumen extraction was concluded to be the cause of substantial differences in particle size distributions and degree of dispersion of the comparable caustic and non-caustic fine tailings. The degree of dispersion was consistent with predictions for dispersed clays established by the sodium adsorption ratio (SAR) values for these materials. The biggest advantage of non-caustic fine tailings and treating caustic fine tailings with coagulant is an increased initial settlement rate and slightly increased hydraulic conductivity at higher void ratios. Thereafter, compressibility and hydraulic conductivity are governed by effective stress. The chemical characteristics of fine tailings (water chemistry, degree of dispersion) do not have a significant impact on their compressibility behaviour and have only a small influence at high void ratio (low effective stress). Fine tailings from a caustic based extraction process had relatively higher shear strengths than comparable non-caustic fine tailings at equivalent void ratios. However, shear strength differences were small and the overall impact on consolidation behaviour, which also depends on compressibility and hydraulic conductivity, is not expected to be significant.

No description available.