Biogeochemical Changes During Bio-cementation Mediated by Stimulated and Augmented Ureolytic Microorganisms.

Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that can improve the engineering properties of granular soils through the precipitation of calcite. The process is made possible by soil microorganisms containing urease enzymes, which hydrolyze urea and enable carbonate ions to become available for precipitation. While most researchers have injected non-native ureolytic bacteria to complete bio-cementation, enrichment of native ureolytic microorganisms may enable reductions in process treatment costs and environmental impacts. In this study, a large-scale bio-cementation experiment involving two 1.7-meter diameter tanks and a complementary soil column experiment were performed to investigate biogeochemical differences between bio-cementation mediated by either native or augmented (Sporosarcina pasteurii) ureolytic microorganisms. Although post-treatment distributions of calcite and engineering properties were similar between approaches, the results of this study suggest that significant differences in ureolysis rates and related precipitation rates between native and augmented microbial communities may influence the temporal progression and spatial distribution of bio-cementation, solution biogeochemical changes, and precipitate microstructure. The role of urea hydrolysis in enabling calcite precipitation through sustained super-saturation following treatment injections is explored

Investigation of Piezocone Dissipation Test Interpretation in Clay Accounting for Vertical and Horizontal Porewater Pressure Dissipation with a Large Deformation Axisymmetric Penetration Model

The piezocone (CPTu) dissipation test is used to characterize how the applied load from the penetrating cone is distributed between the soil and pore fluid during both penetrometer advancement and when penetration is paused. The coefficient of consolidation is often estimated from CPTu dissipation tests by interpreting the rate of excess porewater pressure (∆u) decay to static conditions during a pause in cone penetration. Most CPTu dissipation test interpretation methods are based on Terzaghi consolidation theory for ∆u dissipation at the cone shoulder (u2 position) or cone face (u1 position) and assume that radial ∆u dissipation dominates the response. However, several recent studies show that vertical ∆u migration does contribute to the response. This study uses a large deformation direct axisymmetric cone penetration model to characterize the soil-water mechanical response during CPTu dissipation tests, and in particular, the role of vertical ∆u dissipation on the response at the u1 and u2 positions. Large deformations around the penetrating cone are accommodated with an Arbitrary Lagrangian Eulerian approach. Soil behavior is modeled with the MIT-S1 constitutive model calibrated for Boston blue clay (BBC) soil behavior. ∆u dissipation following undrained cone penetration is simulated with coupled consolidation for BBC with over-consolidation ratios (OCR) of 1, 2, and 4 and a range of hydraulic conductivity anisotropy. The simulated u1 and u2 dissipation responses are presented to study how they are affected by OCR and hydraulic conductivity anisotropy. A correction factor is recommended to account for hydraulic conductivity anisotropy when interpreting the horizontal coefficient of consolidation from CPTu dissipation tests

Effects of Sample Disturbance and Consolidation Procedures on Cyclic Strengths of Intermediate Soils

Sampling and testing of soils to measure engineering properties, such as monotonic and cyclic undrained shear strengths, requires an understanding of the potential effects of sampling disturbance and the selection of appropriate laboratory testing procedures. For clays, past research has provided insights on how sampling methods and laboratory testing procedures can be used in practice to assess and minimize sample disturbance effects. For sands, past research has shown that conventional tube sampling techniques cause excessive disturbance to the soil fabric, such that subsequent measurement of monotonic or cyclic strengths can be greatly in error and misleading. For intermediate soils, the effects of disturbance and consolidation procedures on monotonic and cyclic strengths are not well understood. In the present study, a test protocol was developed to assess the effects that disturbance during sample extrusion, trimming, and mounting have on subsequent measurements of compressibility, monotonic undrained strength, and cyclic undrained strength. Detailed laboratory tests were performed on tube samples from deposits of low-plasticity silty clay, for which conventional sampling and testing were expected to work reasonably well, and low-plasticity clayey sand, for which the effects of sample disturbance were of primary concern. Test results using this protocol for these two soils are presented and discussed

Reusable Instrumented Test Pile Phase 2

65A0481The performance and constructability of pile foundations in coarse granular soils contains significant uncertainty due to challenges in site characterization and uncertainty in pile prediction methods. The Reusable Test Pile idea was conceived as a large diameter instrumented test pile that could be deployed during the site investigation phase of a project where a deep foundation design and or coarse grained soils were expected. Static and dynamic data obtained by the RTP during this phase was envisioned to be useful to designers and contractors for assessing soil properties, pile drivability, and pile performance (capacity, displacement). This report contains four journal papers and a M.S.C.E. thesis that describe the equipment design, data collected, and data processing and interpretation as it applies to evaluating penetration resistance, soil properties, pile driving dynamics, and static pile loading behavior. This includes an initial formulation for static pile capacity estimation based on RTP data and considerations for dynamic pile modeling

Microscale observation and modeling of soil-structure interface behavior using particle image velocimetry

The shearing behavior of a soil-structure interface governs the response of many geotechnical systems, in particular piled foundations. The shaft resistance of piled foundations is known to degrade with cyclic loading, although the governing mechanism is not well understood. This paper presents the results of a laboratory soil-structure investigation in which internal specimen deformations were obtained using particle image velocimetry (PIV) and the normal confining stress was permitted to vary according to a constant normal stiffness (CNS) condition. The PIV measurements showed the shear deformation and volume change to be concentrated within a shear band with a thickness of 5-7 particle diameters adjacent to the interface. During a single cycle the volume change within the shear band began with an initial contraction, followed by dilation to the failure envelop. For the cycling amplitude investigated this response led to a net specimen contraction. The benefit of quantifying the thickness and contraction of the shear band using PIV is that the progressive decrease in void ratio of the shear band can be linked to the limiting value imposed by the minimum void ratio. This provides a framework in which the contraction of the specimen depends on the potential contraction expressed as the difference between the current and minimum void ratio. A model for this contraction is presented, and linked to the decay in normal stress and the limiting loss of interface friction. This framework clarifies the mechanism of friction fatigue during installation and loading of displacement piles in sand.</p

Interface load transfer degradation during cyclic loading: a microscale investigation

The shaft capacity of piles in sand subjected to cyclic (wave) loading has been observed to decrease significantly with loading cycles (Poulos, 1989). A number of researchers (Boulon and Foray, 1986; Tabucanon et al., 1995; Shahrour et al., 1999) have replicated the characteristics of the load transfer degradation behavior in the laboratory through cyclic interface shear testing with a constant normal stiffness confinement condition (Vesic, 1972). However, no consensus currently exists as to the primary microscale mechanisms that govern cyclic interface shear behavior and load transfer degradation. A research program was undertaken to quantify the contribution of soil properties, cementation, confinement condition, and displacement mode, in load transfer degradation. Monotonie and cyclic interface shear tests were performed using a modified interface direct shear device with a Perspex side window. The specimen particle displacement fields were quantified during selected cycles by capturing high resolution digital images (1600 × 1200 pixels) and using Particle Image Velocimetry (White et al., 2001a). Results indicate that the confinement condition, which is intended to replicate the elastic response of the far-field soil, is of primary importance as it allows for normal stress relaxation with soil contraction adjacent to the interface. The displacement magnitude, particle characteristics, and particle-particle cementation were also observed to affect the magnitude and rate of degradation. It is anticipated that these findings will provide a fundamental rationale to identify field conditions where shear stress degradation is likely to occur and a basis from which more rigorous models may be developed.</p

Evaluation of self-penetration potential of a bio-inspired site characterization probe by cavity expansion analysis

Site investigations at limited-access project sites often require mobilization of smaller rigs that may not have the reaction mass required to perform soundings to the desired depth. This study explores the feasibility of a new conceptual bio-inspired solution by adapting functional principles from organisms whose primary mode of locomotion is soil burrowing, including razor clams, caecilians, and earthworms. These organisms radially expand a segment of their body to increase the normal radial pressure acting on it to temporarily form an anchor. This study evaluates the dimensions required for self-penetration of an idealized bio-inspired probe consisting of a radially expanding shaft and a penetrating tip. Cavity expansion analyses, field test data, and theoretical relationships from the literature are used to evaluate the self-penetration potential in different soil types. The results indicate that the resistance to self-penetration is higher in dense sands than in silts and clays. In sands, the resistance to self-penetration is greater for sands that exhibit a more dilative behavior at a given overburden pressure. On the contrary, the resistance to self-penetration in clays decreases slightly as the overconsolidation ratio is increased. The relative dimensions required to initiate self-penetration predicted by cavity expansion analysis are compared with the dimensions of various burrowing organisms.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Axisymmetric Simulations of Cone Penetration in Saturated Clay

A direct axisymmetric cone-penetration model developed for use with a user-written implementation of the MIT-S1 constitutive model is presented. The penetration model uses a finite-difference program with an Arbitrary Lagrangian Eulerian algorithm that couples the program’s large-deformation Lagrangian formulation with user-written algorithms for rezoning and second-order Eulerian advection remapping. Numerical examples illustrate the performance of the remapping and advection algorithms and cone-penetration simulations. Cone penetration at a Boston blue clay site is simulated with the Mohr-Coulomb, modified Cam clay, and MIT-S1 constitutive models and compared with measured cone-penetration test profiles. Single-element simulations illustrate that the MIT-S1 constitutive model captures the significant undrained shear-strength anisotropy exhibited by Boston blue clay, whereas the modified Cam clay and Mohr-Coulomb models do not. Penetration simulations demonstrate the important effect of undrained shear-strength anisotropy on the cone tip resistance, as well as on stress and pore pressure fields around the cone tip and rod

Biogeochemical Changes During Bio-cementation Mediated by Stimulated and Augmented Ureolytic Microorganisms.

Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that can improve the engineering properties of granular soils through the precipitation of calcite. The process is made possible by soil microorganisms containing urease enzymes, which hydrolyze urea and enable carbonate ions to become available for precipitation. While most researchers have injected non-native ureolytic bacteria to complete bio-cementation, enrichment of native ureolytic microorganisms may enable reductions in process treatment costs and environmental impacts. In this study, a large-scale bio-cementation experiment involving two 1.7-meter diameter tanks and a complementary soil column experiment were performed to investigate biogeochemical differences between bio-cementation mediated by either native or augmented (Sporosarcina pasteurii) ureolytic microorganisms. Although post-treatment distributions of calcite and engineering properties were similar between approaches, the results of this study suggest that significant differences in ureolysis rates and related precipitation rates between native and augmented microbial communities may influence the temporal progression and spatial distribution of bio-cementation, solution biogeochemical changes, and precipitate microstructure. The role of urea hydrolysis in enabling calcite precipitation through sustained super-saturation following treatment injections is explored