Chiloro Fund Research Summary Submitted: November 21,2005

Meghan Lithgow Chiloro Fund Research Summary Submitted: November 21,2005

Subsurface vertical barriers (slurry walls) are used in a variety of both environmental and structural applications in civil engineering. In environmental remediation projects, barriers can be used to impede the migration of contaminants. When the barrier is in place, contaminated water is diverted from further permeating the soil layers through rock fractures or underneath dams and levees. Barriers also impede clean water from entering any additional remediation systems intended only for the contaminated water, such as a pump and treat system. A new method, the Trench Cutting Remixing (TRD) Deep Wall construction method, is a method pioneered by the Japanese that cuts and mixes existing soil with injected solidifying agents using large, chainsaw-like equipment. This technology can be used to construct both vertical and inclined barrier walls in a variety of applications such as riverbed stabilization, saltwater intrusion, and environmental remediation projects. In this paper, slurry walls will be discussed and evaluated with emphasis on their use in environmental remediation projects; that is, their materials will be have high compressive strength and low permeability. Specifically, the goals of this study were to examine: (1) The hydraulic conductivity and unconfined compressive strength of soil-slag-CB mixtures typical of those formulated in the Trench Cutting Remixing Deep (TRD) Wall construction method, (2) the influence of various mix proportions on the strength and hydraulic conductivity of the resulting mixtures, (3) the effect of a sandy soil in the slag-CB mixture, and (4) the change in material properties over time.

For this study, the cementitious material to bentonite-water slurry ratio of the mixture was held constant at 15%. The amount of slag used to replace the Portland cement in this 15% cementitious portion, however, varied in amounts of 0, 50, and 85%. Soil was added to the slurry and cementitious blend in a ratio of2.0 parts soil to 1.0 part blend, by volume. All samples were cured initially for a period of 14 days at 100% humidity. After curing, samples underwent permeability tests and after 28 days, unconfined compression tests. Additional permeability tests were performed at two months arid three months to examine the impact of curing time on the hydraulic conductivity. As labeled in two paragraphs previous to this one, the results for each objective are as follows:

(1) By the end of the summer, hydraulic conductivity had been performed on all bentonite- slurry samples at 14 days, 28 days, and three months. The samples are currently curing in buckets are the six month permeability tests will be completed in January to be included in m_ thesis. Testing showed that samples containing 85% slag-replacement had the highest unconfined compressive strength and the lowest permeability at 28 days. Twenty-eight day unconfined compressive strengths for the zero, 50, and 85 percent replacement samples were approximately 170, 230, and 920 kPa, respectively. Samples containing no slag replacement and 50 percent slag- replacement were more permeable than samples containing 85 percent slag replacement. Long-term permeability testing at two months and three months showed that the hydraulic conductivity continued to decrease through three months and the samples with 85 percent slag-replacement remained the least permeable samples through out all tests.

(2) For the initial study, slag was to replace the total amount of cementitious material (Portland cement) in percentages of 0, 50 and 85. The selection of these percentages were similar to those selected in a previous study (Opdyke, 2001) and served as a proper base to expand upon in future testing. After an extensive literature search and review, mix proportions were determined to be two parts sand to one part blend. This ratio is in accordance with mixtures commonly used in grouts where no additives are needed to ensure flowability in the field. The values of slag replacement were varied enough to find an overall trend and were comparable to previous results found for slag-replacement permeabilities and unconfined compressive strengths (Trietley, 1999, Opdyke, 2001). (3) The effect of a sandy soil in the mixture is part of the results shown, and current testing is further investigating this effect. In comparison published results, samples containing a sandy soil tend to be more dense, though "trade off' in slightly higher permeabilities than other soils such as clay or other fine-grained materials.

(4) As discussed in part (1), long-term testing has showed that permeability continues to decrease over time and six-month testing will provide further insight to this phenomenon.

(5) Additional proposed testing included X-Ray Diffraction testing and analysis within the Geology Department under the guidance of Brad Jordan. However, a fellow student (Lance Finnefrock) experienced many delays and inconclusive results with a variety of testing procedures and multiple samples were run before a workable procedure was determined. Because this date was at the end of the summer, the XRD testing was rescheduled to be completed at a later time during the next phase of the research in the fall. The XRD testing will be used to qualitatively determine the rate at which the clay constituents react with other materials in blend such as Portland cement and slag. The samples examined in the XRD testin_ will not be selected until permeability and unconfined compressive strength testing is complete so that optimum samples can be tested. (These "optimum" samples will have a lower permeability and higher compressive strength than the others.) The research this summer provided a base upon which to attempt to replicate the results obtained using attapulgite and sepiolite (two similar swelling clays) in the clay slurry. Additionally, compatibility tests will be performed in three months on all new samples of these two clays using aniline and magnesium sulfate to determine their resistance to aggressive permeants such as those found in landfills or in contaminated groundwater.