A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Evaluating Performance of Conical Filter Systems Using Numerical and Laboratory Methods(2022) Ryoo, Sung Chun; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A significant contributor to retaining wall failure occurs due to inadequate drainage in the backfill. Studies showed 33% of retaining wall failures around the world occurred due to missing or inadequate drainage systems. Even though failure caused by drainage is high, very few United States Departments of Transportation are specific about the backfill material allowed. Traditional weep hole design makes use of pipes perpendicular or parallel to the wall to promote filtration; often covered with a geosynthetic for soil retaining purposes. This study seeks to determine the performance of a recent pore pressure mitigation system through the usage of conical geotextile filters and to investigate an alternative numerical method to effectively determine the type of geotextile in these filters.A numerical model based on a computational fluid dynamics and discrete element method (CFD-DEM) coupled approach was developed to simulate particle movement in the graded filter zone and piping through the geotextiles located in retaining wall backfills. The model was used for conventional as well as conical geotextile filter systems that use a series of woven and nonwoven geotextiles filtering backfill soils with varying fines contents. Poisson line processes and image processing techniques were used to study the pore structure of the nonwoven geotextiles. The results indicated that conical filter systems contribute to higher soil piping rates but provided higher permeability than conventional geotextile filtration system counterparts. The model predictions compared with the laboratory measurements indicated that the movement of particles (i.e., suffusion) influenced the soil-geotextile contact zone permeabilities and caused a decrease in system permeabilities. A retention ratio, αsl, successfully predicted piping rates for different types of woven and nonwoven geotextiles with a percent error range of 13-30%, and was converted into a performance chart. A machine learning algorithm was implemented to create woven and nonwoven zones within the performance curves. Overall, the model predictions were comparable to the laboratory results, suggesting the applicability of the model. Once validation was complete, a conversion retention ratio, αc, was developed for practical usage of the performance charts.Item HYDRAULIC COMPATIBILITY OF GEOTEXTILE-COMPOST SYSTEMS IN LANDFILL COVERS(2019) Ryoo, Sung Chun; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As annual generation of municipal solid waste increases every year, sustainable practices must be promoted in landfill construction. Landfill covers are required by federal regulation to cap the municipal solid waste and to prevent leachate formation. The use of compost as the vegetative layer in landfill final covers is one way to improve the sustainability of landfills. Current literature on compost shows it to be a superior vegetative facilitation material compared to the traditional topsoil material. In order to successfully use compost in landfill cover applications, hydraulic compatibility of the compost and underlying geotextile filters must be adequate. The hydraulic compatibility of various compost, topsoil, and geotextiles have been explored by performing long-term filtration (LTF) tests. Upon completion of the LTF tests, particle size analysis, permittivity tests, piping measurements, and image analysis were conducted to determine clogging and retention performances. When the clogging ratios and piping measurements were considered, every compost-geotextile and topsoil-geotextile combinations yielded acceptable clogging and retention performance. A parametric study was conducted to determine if different characteristic pore size and grain sizes influenced the laboratory observed clogging ratios; currently, no relationships exist. Existing filter selection criteria successfully predicted retention behavior and failed to predict clogging behavior. Conducting more soil-geotextile compatibility tests will be needed to propose a new filter criterion for clogging. Based on limited LTF data, compost is not likely to promote clogging in geotextiles; however, additional leaching and geotechnical tests are required to assess the nutrient leaching and shear behavior of compost layers on landfill cover slopes.