Jason T. DeJong

Effects of environmental factors on microbial induced calcium carbonate precipitation.

Aims:  To gain an understanding of the environmental factors that affect the growth of the bacterium Sporosarcina pasteurii, the metabolism of the bacterium and the calcium carbonate precipitation induced by this bacterium to optimally implement the biological treatment process, microbial induced calcium carbonate precipitation (MICP), in situ.

Experimental Optimization of Microbial-Induced Carbonate Precipitation for Soil Improvement

AbstractImplementation of laboratory-tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates. Microbial-induced carbonate precipitation (MICP) holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate. The study presented herein focuses on controlling MICP treatment of one-dimensional flow, half-meter-scale column experiments. Treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates, flow direction, and formulations of biological and chemical amendments. Monitoring of column experiments included spatial and temporal measurements of the physical, chemical, and biological properties essential to the performance of MICP, including shear wave velocity, permeability, calcium carbonate content, aqueous calcium, aqueous ammonium, aqueous urea, and bacterial density. Rela...

Soil engineering in vivo: harnessing natural biogeochemical systems for sustainable, multi-functional engineering solutions

Carbon sequestration, infrastructure rehabilitation, brownfields clean-up, hazardous waste disposal, water resources protection and global warming—these twenty-first century challenges can neither be solved by the high-energy consumptive practices that hallmark industry today, nor by minor tweaking or optimization of these processes. A more radical, holistic approach is required to develop the sustainable solutions society needs. Most of the above challenges occur within, are supported on, are enabled by or grown from soil. Soil, contrary to conventional civil engineering thought, is a living system host to multiple simultaneous processes. It is proposed herein that ‘soil engineering in vivo’, wherein the natural capacity of soil as a living ecosystem is used to provide multiple solutions simultaneously, may provide new, innovative, sustainable solutions to some of these great challenges of the twenty-first century. This requires a multi-disciplinary perspective that embraces the science of biology, chemistry and physics and applies this knowledge to provide multi-functional civil and environmental engineering designs for the soil environment. For example, can native soil bacterial species moderate the carbonate cycle in soils to simultaneously solidify liquefiable soil, immobilize reactive heavy metals and sequester carbon—effectively providing civil engineering functionality while clarifying the ground water and removing carbon from the atmosphere? Exploration of these ideas has begun in earnest in recent years. This paper explores the potential, challenges and opportunities of this new field, and highlights one biogeochemical function of soil that has shown promise and is developing rapidly as a new technology. The example is used to propose a generalized approach in which the potential of this new field can be fully realized.

Shear failure behavior of granular–continuum interfaces

Abstract Particulate–continuum interfaces (e.g. soil–concrete, soil–steel, soil–geomembranes) determine the behavior of many geotechnical structures including deep foundations, synthetic impervious liners, trenchless technologies, and an assortment of earth retaining structures. Therefore, proper understanding of the localized shearing mechanisms that govern their behavior is essential if geotechnical design is to improve. This paper presents a summary of recent research on the coupled effect of surface roughness and hardness on interface shear behavior and strength. This was accomplished through performing a series of laboratory tests on a selection of sand–continuum material interfaces and through discrete element modeling of particulate–continuum interfaces.

Stress-Strain Behavior of Sands Cemented by Microbially Induced Calcite Precipitation

AbstractMicrobial induced calcite precipitation (MICP) is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil. The evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests. MICP treated sands with cementation levels ranging from young, uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear. A transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed. Moderately cemented specimens are subjected to various stress paths, which result in a change to the shear strength and volumetric behavior. Shear wave velocity is used to nondestructively monitor the change in small-strain stiffness during shearing, which provides an indication of cementation degradation as a function of strain level. Because shear wave velocity is influenced by ...

Evaluation of Undrained Shear Strength Using Full-Flow Penetrometers

Full-flow penetrometers (the T-bar and ball) are increasingly used on sites with thick deposits of soft clays, particularly prevalent offshore. Full-flow penetration tests were performed at five international well-characterized soft clay test sites to assess the use of full-flow penetrometers to estimate undrained shear strength. Field vane shear data were used as the reference undrained strength. Statistical analyses of strength factors indicates that full-flow penetrometers provide an estimate of undrained shear strength at a similar level of reliability compared to the piezocone. Relationships for estimating the strength factor and soil sensitivity using only full-flow penetrometer data obtained during initial penetration and extraction are developed. A strong dependence of the strength factor on sensitivity was identified and can be used for the estimation of undrained strength. The effectiveness and use of the developed correlations are demonstrated through their application at an additional test site.

Fabrication, Operation, and Health Monitoring of Bender Elements for Aggressive Environments

Bender elements are commonly used to monitor the shear wave velocity of soils in various tests, including triaxial, consolidation, and centrifuge tests. When used in aggressive soil environments, electromagnetic crosstalk can distort the received bender element signal, preventing accurate shear wave velocity measurements. Aggressive soil environments are defined herein as conductive soils with high relative permittivity. Under these conditions, the electrical source is transmitted from source to receiver bender, dominating any received shear wave signal propagating through the soil. Careful attention must be paid to reducing the transmission of the electromagnetic signal, particularly in aggressive soil environments. When the waterproof coating of a bender element degrades and the inner and outer electrodes become electrically connected in a saturated environment, the bender element will no longer operate. However, when the waterproofing material is degraded so that only a single electrode on the source element is exposed, electric current can enter the pore fluid and affect the received signal. Further, even if the waterproofing coating is intact, electromagnetic crosstalk from the induced electrical field generated by the transmitting bender element can still affect the received signal when the conductivity of the pore fluid is high. Bender elements can be constructed so as to greatly reduce the electromagnetic crosstalk, and simple tests can be performed to help ensure that the bender element system is not susceptible to crosstalk. The objective here is to present details and practical guidelines regarding the fabrication, operation, and health monitoring of bender elements that will help ensure clear shear wave velocity measurements in aggressive soil environments. The fabrication steps presented improve on previous recommendations. Bender element operation (including signal form, frequency, and amplitude) also affects signal quality and the accuracy of the measured travel time. Finally, recommendations for monitoring the health of the bender elements throughout the transducer life are outlined.

Evaluation of Remolded Shear Strength and Sensitivity of Soft Clay Using Full-Flow Penetrometers

The undrained remolded shear strength of soft clays is of importance in geosystem design, particularly for offshore structures. Common methods to estimate remolded shear strength, such as correlations with cone penetration data, direct measurement with an in situ field vane shear device, and laboratory measurements, produce varied results and can be particularly costly and time consuming. Full-flow penetrometers (T-bar and Ball) provide an alternative rapid method to estimate remolded shear strength and soil sensitivity through remolding soil by repeated cycling of the penetrometer up and down over a given depth interval. The cyclic penetration resistance degradation curve inherently contains information regarding remolded strength and sensitivity. The objective of this paper is to assess the ability of full-flow penetrometers to predict remolded strength and soil sensitivity, and to develop a suite of predictive correlations in which these properties can be estimated in the absence of complementary laboratory or in situ test data. To accomplish this, full-flow penetration profiles and cyclic tests were performed at five well characterized soft clay sites, which together represent the broad range of soils in which the penetrometers will be often used. A previously developed model for the reduction in penetration resistance with cycling is modified to predict the entire degradation curve, including the remolded penetration resistance using only measurements obtained during initial penetrometer penetration and extraction. Using field vane shear strength as the reference measurement, correlations are developed to predict soil sensitivity and remolded shear strength based solely on full-flow penetrometer data, which is particularly useful in site investigation programs where site specific data are not yet available or are sparse. Finally, the usefulness of these relationships is demonstrated by implementing them for two additional soft clay sites.

Seismic and Resistivity Measurements for Real-Time Monitoring of Microbially Induced Calcite Precipitation in Sand

A variety of biogeochemical processes, from inorganic mineral precipitation to bio-film formation to bio-gas generation, are being investigated as alternative methods to improve soil properties. Every process applied in a geotechnical application requires the ability to monitor the progression of treatment, preferably in real time. While monitoring of the biogeochemical processes is necessary to properly apply and manage the treatment process, ultimately verification that the treatment is improving the engineering soil properties as desired is necessary. Because direct measurements of soil properties (e.g., strength tests) during treatment are infeasible, the use of indirect non-destructive measurements during treatment is desirable. Development of these real-time, non-destructive measurements would increase the “certainty of execution” of bio-treatment methods. To this end, seismic velocity, and resistivity measurements are examined herein to assess their ability to monitor the extent and spatial distribution of microbially induced calcite precipitation (MICP) in sands. Shear wave velocity (S-wave) test results are used to develop a generalized correlation to the precipitated calcite mass; this in turn enables prediction of changes in void ratio (porosity), density, and shear modulus during treatment. Compression wave velocity (P-wave) measurements are determined under different saturation conditions and used in combination with S-wave measurements to observe how the Poisson’s ratio evolved during treatment. The applicability of resistivity measurements for monitoring the MICP treatment process is also examined. Finally, the seismic properties of MICP treated sand are compared with other conventional materials and the implications of these results for real-time monitoring during future field-scale applications discussed.

Influence of Partial Consolidation during Cone Penetration on Estimated Soil Behavior Type and Pore Pressure Dissipation Measurements

Estimation of soil behavior type from cone penetration testing, and the interpretation of dissipation tests, is complicated in in- termediate soil types, such as silty sands, sandy silts, etc., where partial consolidation occurs during penetration. This issue is investigated in this paper using results from cavity expansion and finite element analyses as well as field and centrifuge piezocone data. The implications for soil classification are examined using analytical expressions to explore the effect of normalized shear strength, rigidity index, and over- consolidation ratio relative to the influence of partial consolidation and viscous effects under fully undrained conditions. It is shown that partial drainage conditions can affect where data plots on soil behavior charts, thus complicating soil classification. The effect on dissipation tests following partial consolidation during cone penetration is shown to create errors in interpretation using experimental and numerical data. A new approach is developed based in part on manipulation of solutions for pore pressure dissipation (following undrained penetration) to account for these errors when interpreting dissipation tests. Errors can become significant during standard cone penetration testing when the t50 dissipation time is less than about 50 s. Guidelines, including equations and a chart, are presented for practical use. Finally, imple- mentation of this approach is demonstrated in a brief case study. DOI: 10.1061/(ASCE)GT.1943-5606.0000646.