Dept of Civil & Environmental Engineering, University of Maryland

Research Projects

Microbiologically Mediated Soil Improvement

Biological processes may provide great and previously unexplored opportunities for in situ, cost effective soil improvement. This research study evaluates previously untested naturally occurring microbiological sequences that may be manipulated to dramatically improve the strength and stiffness of soil. The process aimed to replicate is the natural process that occurs when calcium carbonate precipitates in granular soil, resulting in a strongly cemented soil.

SEM photomicrographs of samples subjected to Myxococcus xanthus-induced calcite precipitation. (a) Control (i.e., calcium-rich slab stone not submitted to biomineralization) showing spalling and fissuring of calcite crystals along planes (see zone A), (b) Calcified bacteria blanketing stone samples (see zone B). (After Rodriguez-Navarro et al. 2003).

Filtration and Dewatering Performance of Geotextile Containers

Filtration and dewatering behavior of geotextile containers with fly ash and dredged sediments is studied. The study involves long-term flow testing of single and two-layer geotextile systems with unusual geomaterials. Hydraulic compatibility of recycled materials with geotextiles is investigated.

Remediation of Petroleum Contaminated Soils

Effect of various innovative binders on the chemical fixation of organic contaminants in petroleum-contaminated soils is being studied through geotechnical and environmental tests. The project includes investigation of capacity of those binders to adsorb petroleum products. Soil stabilization and groundwater remediation (i.e. permeable reactive barrier) applications are studied.

Evaluation of Geosynthetic Strain Distribution Using Image Analysis

Current strain determination methods employed as part of tensile tests mostly assume that the strain is uniform throughout the specimen and, hence, are incapable of determining local strains. Geosynthetics have occasionally been instrumented with strain gages and extensometers; however, these direct contact methods have limitations in fully defining strain distributions in a test specimen. Optical flow techniques are being used in the study to define the strain distribution in various geosynthetics during wide-width tensile tests conducted using roller and hydraulic grips.

Modeling Pore-Scale Flow in Asphalt Concrete

The objective is to model the water flow through asphalt concrete using X-ray computerized tomography. Image processing algorithms are being used to process the three-dimensional images of asphalt concrete. Effect of different variables on the permeability has been studied. Three-dimensional flow through asphalt pavements has been modeled and directional permeabilities are determined using the lattice Boltzmann technique.

Use of Image Analysis for Geotextile Pore Structure Characterization

Filtration performance of geotextiles strongly depends on their pore structure parameters, i.e. percent open area (POA), pore opening size distribution (PSD) and constriction size distribution (CSD). Current methods of determination of pore structure parameters contain inherent disadvantages whereas image analysis can be used effectively for this purpose. Two new image-based PSD and CSD determination methods and a new image-based POA determination method are developed specifically for woven and nonwoven geotextiles. In this study, mathematical morphology based image operators are being used to define the pore structures. Markov chain models were developed to define the 3-dimensional pore structure of nonwovens. The predictions of the model are checked against laboratory bubble point test-based data independently produced by other researchers.

Remediation of Abandoned Mines Using CCBs

The objective is to evaluate the performance of various controlled low-strength mixes to control acidic mine drainage and support abandoned mine holes. The use of coal combustion by-products (CCBs), including the bottom ash and fluidized bed combustion ash, is promoted in this study. The long-term stewardship of the remediation activity provided important findings for future in-situ mine remediation activities.

Fly Ash Amended Highway Bases

Class F fly ash cannot be used alone in soil stabilization applications as it is not self-cementing. An activator such as Portland cement or lime must be added to produce cementitious products often called pozzolan stabilized mixtures. The main objective of this study is to investigate the beneficial reuse of Class F fly ash amended soil-cement or soil-lime as base layers in highways. A battery of tests is conducted on soil-fly ash mixtures prepared with cement and lime as activators. Results of the study show that the strength of a mixture is highly dependent on the curing period, the compactive energy, cement content, and water content at compaction. Lime treatment does not provide sufficient strength for designing the mixtures as highway bases. A power function in terms of bulk stress used for granular soils can accurately model the resilient moduli.

Remediation of PCB Contaminated Wastewater Treatment Sludges

Various alternatives to remedy the PCB contaminated sludges on one of the U.S. EPA Superfund sites have been investigated. Geosynthetic-supported capping and chemical stabilization is evaluated in this research program. The results of the study were used to develope geotextile filter selection criteria for high water content contaminated geomaterials.

		Research Projects Microbiologically Mediated Soil Improvement Biological processes may provide great and previously unexplored opportunities for in situ, cost effective soil improvement. This research study evaluates previously untested naturally occurring microbiological sequences that may be manipulated to dramatically improve the strength and stiffness of soil. The process aimed to replicate is the natural process that occurs when calcium carbonate precipitates in granular soil, resulting in a strongly cemented soil. SEM photomicrographs of samples subjected to Myxococcus xanthus-induced calcite precipitation. (a) Control (i.e., calcium-rich slab stone not submitted to biomineralization) showing spalling and fissuring of calcite crystals along planes (see zone A), (b) Calcified bacteria blanketing stone samples (see zone B). (After Rodriguez-Navarro et al. 2003). Filtration and Dewatering Performance of Geotextile Containers Filtration and dewatering behavior of geotextile containers with fly ash and dredged sediments is studied. The study involves long-term flow testing of single and two-layer geotextile systems with unusual geomaterials. Hydraulic compatibility of recycled materials with geotextiles is investigated. Remediation of Petroleum Contaminated Soils Effect of various innovative binders on the chemical fixation of organic contaminants in petroleum-contaminated soils is being studied through geotechnical and environmental tests. The project includes investigation of capacity of those binders to adsorb petroleum products. Soil stabilization and groundwater remediation (i.e. permeable reactive barrier) applications are studied. Evaluation of Geosynthetic Strain Distribution Using Image Analysis Current strain determination methods employed as part of tensile tests mostly assume that the strain is uniform throughout the specimen and, hence, are incapable of determining local strains. Geosynthetics have occasionally been instrumented with strain gages and extensometers; however, these direct contact methods have limitations in fully defining strain distributions in a test specimen. Optical flow techniques are being used in the study to define the strain distribution in various geosynthetics during wide-width tensile tests conducted using roller and hydraulic grips. Modeling Pore-Scale Flow in Asphalt Concrete The objective is to model the water flow through asphalt concrete using X-ray computerized tomography. Image processing algorithms are being used to process the three-dimensional images of asphalt concrete. Effect of different variables on the permeability has been studied. Three-dimensional flow through asphalt pavements has been modeled and directional permeabilities are determined using the lattice Boltzmann technique. Use of Image Analysis for Geotextile Pore Structure Characterization Filtration performance of geotextiles strongly depends on their pore structure parameters, i.e. percent open area (POA), pore opening size distribution (PSD) and constriction size distribution (CSD). Current methods of determination of pore structure parameters contain inherent disadvantages whereas image analysis can be used effectively for this purpose. Two new image-based PSD and CSD determination methods and a new image-based POA determination method are developed specifically for woven and nonwoven geotextiles. In this study, mathematical morphology based image operators are being used to define the pore structures. Markov chain models were developed to define the 3-dimensional pore structure of nonwovens. The predictions of the model are checked against laboratory bubble point test-based data independently produced by other researchers. Remediation of Abandoned Mines Using CCBs The objective is to evaluate the performance of various controlled low-strength mixes to control acidic mine drainage and support abandoned mine holes. The use of coal combustion by-products (CCBs), including the bottom ash and fluidized bed combustion ash, is promoted in this study. The long-term stewardship of the remediation activity provided important findings for future in-situ mine remediation activities. Fly Ash Amended Highway Bases Class F fly ash cannot be used alone in soil stabilization applications as it is not self-cementing. An activator such as Portland cement or lime must be added to produce cementitious products often called pozzolan stabilized mixtures. The main objective of this study is to investigate the beneficial reuse of Class F fly ash amended soil-cement or soil-lime as base layers in highways. A battery of tests is conducted on soil-fly ash mixtures prepared with cement and lime as activators. Results of the study show that the strength of a mixture is highly dependent on the curing period, the compactive energy, cement content, and water content at compaction. Lime treatment does not provide sufficient strength for designing the mixtures as highway bases. A power function in terms of bulk stress used for granular soils can accurately model the resilient moduli. Remediation of PCB Contaminated Wastewater Treatment Sludges Various alternatives to remedy the PCB contaminated sludges on one of the U.S. EPA Superfund sites have been investigated. Geosynthetic-supported capping and chemical stabilization is evaluated in this research program. The results of the study were used to develope geotextile filter selection criteria for high water content contaminated geomaterials.