Enzyme-induced carbonate precipitation (EICP) is a biogeotechnical soil improvement method that involves the precipitation of calcium carbonate via hydrolysis of urea (ureolysis) catalyzed by free urease enzyme in a calcium chloride solution. When this reaction takes place in the pore space of a sand, the precipitated calcium carbonate may bind soil grains together, thereby improving strength. Three studies on EICP are presented in this dissertation. In the first study, chemical equilibrium modeling via PHREEQC is used to develop a method for evaluating urease activity from electrical conductivity (EC) measurements in a closed reactor containing urea and urease. It is shown that a commonly used correlation to estimate urease activity from EC measurements overestimates the initial urea hydrolysis rate (thereby overpredicting the urease activity as well). In the second study, the crystal structure and mechanical properties of calcium carbonate minerals formed by EICP are studied. It is shown that a “modified” precipitate synthesized by the inclusion of nonfat dry milk in the EICP solution is more ductile than a “baseline” precipitate synthesized from an EICP solution without nonfat milk. Additionally, in sands biocemented using the modified EICP solution, precipitation occurs preferentially at the grain contacts. This may contribute to relatively high unconfined compressive strengths at low carbonate contents in some EICP-treated sands. The third study discusses the role of some sand characteristics on the strength following modified EICP treatment. Three batches of Ottawa 20-30 sand from different sources were treated identically using the modified EICP solution. Subsequent testing showed large differences in their unconfined compressive strengths. It is shown that this variation in unconfined compressive strength is due to differences in the surface microtexture and surface mineralogy of the sands.The fundamental studies presented in this dissertation provide a deeper understanding of some aspects of the EICP process.

Enzyme-induced carbonate precipitation (EICP) is an emerging technology for ground improvement that cements soil with calcium carbonate to increase strength and stiffness. EICP-improved soil can be used to support new facilities or it can be injected under existing facilities to prevent excessive deformation. The limitations for commercial adoption of EICP are the cost and the lack of implementation at field-scale. This research demonstrated two ways to reduce the cost of EICP treatment at field-scale. The first was a modification to the EICP solution such that lower amounts of chemicals are needed to achieve target strengths. The second was to use a simple and inexpensive enzyme extraction method to produce the enzyme at a large-scale. This research also involved a two-stage scale-up process to create EICP biocemented soil columns using a permeation grouting technique. The first stage was at mid-scale where 0.6 m x 0.3 m-diameter EICP biocemented soil columns were created in boxes. This work confirmed that conventional permeation grouting equipment and methods are feasible for EICP soil treatment because the columns were found to have a uniform shape, the injection method was able to deliver the EICP solution to the edges of the treatment zone, and downhole geophysics was effectively used to measure the shear wave velocity of the biocemented soil mass. The field-scale stage was performed in the Test Pit facility at the Center for Bio-mediated and Bio-inspired Geotechnics' Soils Field Laboratory. Seven biocemented soil columns were created with diameters ranging from 0.3-1 m and heights ranging from 1-2.4 m. Effective implementation at this scale was confirmed through monitoring the injection process with embedded moisture sensors, evaluating the in situ strength improvement with downhole geophysics and load testing, and testing of the excavated columns to measure shear wave velocity, dimensions, carbonate content, and strength. Lastly, a hotspot life cycle assessment was performed which identified ways to reduce the environmental impacts of EICP by using alternative sourcing of inputs and extraction of byproducts. Overall, this research project demonstrates that EICP is a viable ground improvement technique by way of successfully producing field-scale biocemented soil columns.

The focus of this study is statistical characterization of the significant duration of strong ground motion time histories. The significant duration is defined as the time needed to build up between five and seventy five (SD575) and ninety five percent (SD595) of the energy of a strong motion record. Energy is measured as the integral of the square of the acceleration time history and can be used to capture the potential destructiveness of an earthquake. Correlations of the geometric means of the two significant duration measures (SD575 and SD595) with source, path, and near surface site parameters have been investigated using the geometric mean of 2,690 pairs of recorded horizontal strong ground motion data from 129 earthquakes in active plate margins. These time histories correspond to moment magnitudes between 4.8 and 7.9, site to source distances up to 200 km, and near surface shear wave velocity ranging from 120 to 2250 m/s. Empirical relationships have been developed based upon the simple functional forms, and observed correlations. The coefficients of the independent variables in these empirical relationships have been determined through nonlinear regression analysis using a random effects model. It is found that significant duration measures correlate well with magnitude, site to source distance, and near surface shear wave velocity. The influence of the depth to top of rupture, depth to the shear wave velocity of 1000 m/s and the style of faulting were not found to be statistically significant. Comparison of the empirical relationship developed in this study with existing empirical relationships for the significant duration shows good agreement at intermediate magnitudes (M 6.5). However, at larger and smaller magnitude, the differences between the correlations developed in this study and those from previous studies are significant.