Microbial Geotechnology is a new branch of geotechnical engineering that deals with the applications of microbiological methods to geological materials used in engineering. The aim of these applications is to improve the mechanical properties of soil so that it will be more suitable for construction or environmental purposes. Two notable applications, bioclogging and biocementation, have been explored. Bioclogging is the production of pore-filling materials through microbial means so that the porosity and hydraulic conductivity of soil can be reduced. Biocementation is the generation of particle-binding materials through microbial processes in situ so that the shear strength of soil can be increased. The most suitable microorganisms for soil bioclogging or biocementation are facultative anaerobic and microaerophilic bacteria, although anaerobic fermenting bacteria, anaerobic respiring bacteria, and obligate aerobic bacteria may also be suitable to be used in geotechnical engineering. The majority of the studies on Microbial Geotechnology at present are at the laboratory stage. Due to the complexity, the applications of Microbial Geotechnology would require an integration of microbiology, ecology, geochemistry, and geotechnical engineering knowledge.

Applications of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ

This paper presents a comprehensive review of published literature on soil piping phenomena. The first tools to design earth dams to resist piping were developed during 1910–1935. Filter criteria for dispersive soils was refined in the 1970’s. Piping phenomena are generally defined as: (1) heave, (2) internal erosion, (3) backwards erosion, although other modes are possible. Recent work on piping highlights the limitations of the occurrence of piping and the role that design and construction may play in a large percentage of piping failures. Standardized laboratory procedures are available to assess piping potential in cohesive materials, but no such methods exist for non-cohesive soils. However, methods are available for evaluation of self-filtration potential. Recent advances in computer technology have facilitated the evaluation of seepage and deformation in embankments but computational methods for evaluation of piping potential are currently limited.

Critical appraisal of piping phenomena in earth dams

Clogging of stormwater gravel infiltration systems and filters: insights from a laboratory study.

Predicting the impact of biochar additions on soil hydraulic properties

The ability of in-place pervious concretes to effectively drain storm water runoff gradually reduces as it becomes clogged due to the ingress of fine particles into its pore structure. This study systematically investigates several pervious concrete mixtures propor- tioned using different size aggregates and their blends on their propensity to clogging so as to bring out the influence of pore structure features on particle retention and the consequent permeability reduction. A finer and a coarser sand are used as clogging materials and the experimental study on permeability reduction as a result of particle retention is carried out using a falling head permeability cell. Significant permeability reductions are observed when finer sand is used as the clogging material. A certain effective pore size to clogging particle size ratio is found in this study, that is most conducive to particle retention. Thus pervious concrete specimens of similar porosity, having very large 5-6 mm or very small 1-2 mm pore sizes are found to be less susceptible to clogging under the conditions of this study. An idealized three-dimensional geometry obtained from two-dimensional planar images of pervious concrete sections is used, along with a probablistic particle capture model to predict particle retention associated with clogging material addition and simulated runoff. The trends in the predicted particle retention and the experimentally determined permeability reduction agree well. A "clogging potential" is defined in this paper, either as a ratio of the porosity reduction because of clogging to the initial porosity, or as a ratio of the permeability reduction to the permability in the unclogged state. DOI: 10.1061/ASCEMT.1943-5533.0000079 CE Database subject headings: Concrete; Clogging; Porosity; Permeability; Experimentation. Author keywords: Pervious concrete; Pore structure; Clogging; Porosity; Permeability; Clogging potential; Particle capture model.

Permeability Reduction in Pervious Concretes due to Clogging: Experiments and Modeling

Soil filters, which are commonly used to provide stability to the base soils in subsurface infrastructure, are prone to long-term accumulation of fine micron-sized particles. This causes reduction in the permeability, which in turn may lead to intolerable decreases in their drainage capacity. In this paper, the extent of this reduction is addressed using results from both experimental and theoretical investigations. In the experimental phase, a sandy soil commonly used as a filter or drainage layer was subjected to pore fluids containing polystyrene or kaolinite particles, and their permeability reductions were determined in terms of the pore fluid suspension parameters. In the theoretical phase of the investigation, a representative elemental volume of the soil filter was modeled as an ensemble of capillary tubes and the permeability reduction due to physical clogging was simulated using basic principles of flow in cylindrical tubes. The results from the experimental and theoretical investigations were in good agreement. In general, the permeability reduced by more than one order of magnitude, even when the migrating particles were smaller than the majority of the soil filter pores. The concentration of particles in the pore stream affected the rate at which the permeability reduced. Self-filtration of particles, which is prominent at higher flow rates, may itself lead to a 20% reduction in the permeability for these sands.

Permeability Reduction of Soil Filters due to Physical Clogging

In this study, the differences in soil filter clogging are evaluated under two operating conditions: constant head and constant flow rate. Whereas filters placed around well screens and leachate collection systems are subjected to a constant flow rate, filters in earth dams and pavement drainage systems operate under constant or slightly varying heads. In this study, the experiments revealed similar permeability reductions with respect to time in both cases; however, the permeability reduction under the condition of constant head occurred in much fewer pore volumes than under the condition of constant flow rate. Self-filtration appeared to be greater under the condition of constant head. The physical clogging model developed for the conditions of constant flow rate and constant head showed good qualitative agreement with experimental observations.Key words: particle, clogging, filter, constant, head, flow.

/pdf/physical-clogging-of-soil-filters-under-constant-flow-rate-2jo0cj0c2s.pdf

Physical clogging of soil filters under constant flow rate versus constant head

The effects of ionic strength of the permeating fluid on the clogging of soil filters and drainage layers are addressed using both experimental and modeling investigations. In the experimental phas...

Malay G. Hajra

Papers

Permeability Reduction of Soil Filters due to Physical Clogging

Physical clogging of soil filters under constant flow rate versus constant head

Effects of Ionic Strength on Fine Particle Clogging of Soil Filters

Biological Clogging in Porous Media