@article{faeli_montoya_gabr_2024, title={Development of a reactive transport model for microbial induced calcium carbonate precipitation in unsaturated conditions}, volume={3}, ISSN={["1208-6010"]}, DOI={10.1139/cgj-2022-06771}, journal={CANADIAN GEOTECHNICAL JOURNAL}, author={Faeli, Zahra and Montoya, Brina M. and Gabr, Mohammed A.}, year={2024}, month={Mar} }
 @article{faeli_montoya_gabr_2023, title={Development of a Reactive Transport Model for Microbial Induced Calcium Carbonate Precipitation in Unsaturated Conditions}, volume={61}, ISSN={0008-3674 1208-6010}, url={http://dx.doi.org/10.1139/cgj-2022-0677}, DOI={10.1139/cgj-2022-0677}, abstractNote={ Microbial induced calcium carbonate precipitation (MICP) offers a sustainable technique to improve geologic properties of soils in engineering structures. The applications encompass improved soil strength, scour mitigation, fracture sealing, and in situ contaminant immobilization. Previous studies have presented fundamental processes and implementation in lab- and field-scale. Most of these studies were examined in saturated conditions despite many MICP applications including those in coastal and riverside areas which will likely take place under unsaturated conditions. The study herein investigated the effect of soil water retention curve (SWRC) parameters and attachment coefficient ( Kat ) on CaCO3 precipitation in sand. Using numerical analyses, a continuum model was developed in which unsaturated flow and transport were coupled with biological and chemical reactions in variably saturated conditions. Predictive modeling results compare mass percentage of calcium carbonate resulting from MICP at degrees of soil water saturations of 20%, 40%, 80%, and 100% in sandy soil media. The results indicate the bacteria attachment coefficient increases by a factor of 3 as the degree of saturation is decreased from 100% to 20%, as the higher suctions at lower saturation levels improve bacteria fixation. The drying branch of SWRC versus wetting front yields higher CaCO3 for identical MICP treatment. Numerical results show the trend in hydraulic conductivity with increasing cementation level. }, number={4}, journal={Canadian Geotechnical Journal}, publisher={Canadian Science Publishing}, author={Faeli, Zahra and Montoya, Brina M. and Gabr, Mohammed}, year={2023}, month={Aug}, pages={827–835} }
 @article{faeli_montoya_gabr_2023, title={Elucidating factors governing MICP biogeochemical processes at macro-scale: A reactive transport model development}, volume={160}, ISSN={0266-352X}, url={http://dx.doi.org/10.1016/j.compgeo.2023.105514}, DOI={10.1016/j.compgeo.2023.105514}, abstractNote={Microbial Induced Calcium Carbonate Precipitation (MICP) influenced by biofilm metabolism in the subsurface can be exploited for a variety of engineered applications encompassing geotechnical ground improvement, environmental bioremediation, and hydraulic barriers. A reactive transport model was developed to determine the effects of controlling factors in terms of treatment protocols and experimental methods. Six column tests were calibrated and a range for the key parameters was determined. Fifteen key parameters of MICP reactive transport model were assessed in four categories (microbial activity and attachment, sample preparation, treatment protocol, and experiment dimensions). The results emphasized the effects of three main factors of microbial activity, microbial attachment process, and number of treatment (among all 15 assessed parameters) on the calcium carbonate (CaCO3) precipitation content and distribution. An increase in specific ureolysis rate (Ku) and attachment rate coefficient (Kat) by two orders of magnitude improves average CaCO3 by up to 13% and 6%, respectively with non-uniformity (COV) increase of 16%. Higher flow rates and solution concentrations contribute to more uniform CaCO3 distribution. The constant attachment rate model is useful to yield the CaCO3 precipitation profiles but more accurate models are needed to capture exact distribution. Post-treatment hydraulic conductivity, porosity and attached biomass were assessed.}, journal={Computers and Geotechnics}, publisher={Elsevier BV}, author={Faeli, Zahra and Montoya, Brina M. and Gabr, Mohammed A.}, year={2023}, month={Aug}, pages={105514} }
 @article{shahriar_gabr_montoya_ortiz_2023, title={Estimating live-bed local scour around bridge piers in cohesionless sediments: applicability and bias of selected models}, volume={60}, ISSN={["1208-6010"]}, url={http://dx.doi.org/10.1139/cgj-2022-0122}, DOI={10.1139/cgj-2022-0122}, abstractNote={ To design the foundation system of waterway bridges, Load and Resistance Factor Design guidelines suggest use of deterministic scour depth prediction models. Understanding the inherent bias of deterministic scour depth prediction models will advance the development of reliability index-based foundation design regime. Four bridge scour depth prediction models were assessed in terms of two statistical parameters, termed herein mean absolute percentage error (MAPE), and conservatism, percentage of cases the predicted scour depth exceeded the measured scour depth. Live-bed laboratory and field scour depth databases were used in analyses to quantify model scatter by comparatively assessing the computed scour depth versus measured data. For live-bed laboratory data, values of MAPE ranged from 23.5% to 59.8%, whereas conservatism ranged from 28.4% to 97.8%. For live-bed field data, conservatism varied from 93.3% to 95.1%, while MAPE ranged from 205.6% to 319%. Statistical models were applied to ascertain the biasness of the four deterministic models. Accuracy and conservatism of a given model were consequently adjusted through proposed modification factors. The proposed approach allows for the selection of a suitable modification factor to satisfy a target probability of deceedance or a target conservatism. }, number={4}, journal={CANADIAN GEOTECHNICAL JOURNAL}, publisher={Canadian Science Publishing}, author={Shahriar, Azmayeen R. and Gabr, Mohammed A. and Montoya, Brina M. and Ortiz, Alejandra C.}, year={2023}, month={Apr}, pages={471–487} }
 @article{abayo_cabas_chamberlin_montoya_2023, title={Fluvial geomorphic factors affecting liquefaction-induced lateral spreading}, volume={39}, ISSN={["1944-8201"]}, DOI={10.1177/87552930231190655}, abstractNote={ Liquefaction-induced lateral displacements represent a major geohazard in earthquake-prone regions, yet the uncertainty associated with their prediction remains notoriously high. Documented observations after recent earthquakes provide evidence that depositional environment-specific geologic conditions play a crucial role in liquefaction susceptibility, and in the severity and spatial extent of liquefaction-induced ground deformations. However, this evidence is largely qualitative in nature, which limits the potential to incorporate the effects of depositional processes and environments in the next generation of lateral spreading predictive models. This study provides a framework to quantitatively assess the relationship between depositional environment-specific geologic factors and lateral spreading by means of simple fluvial geomorphic facies models, geotechnical engineering data (e.g. Cone Penetration Test data), and geospatial analytics. Three hypotheses are introduced and tested using lateral spreading ground deformations observed following the 2011 Christchurch earthquake along the Avon and Heathcote rivers in New Zealand. The results from this study indicate that the presence of an active (i.e. with active sediment deposition) compared to inactive (e.g. abandoned) channels is the most important fluvial geomorphologic variable out of the three tested. The other two are associated with the location relative to the meander bend position, including location within the point bar (inside) or the cut bank (outside), and upstream versus downstream within a given point bar. Findings from this study show that more lateral spreading occurs within point bars, and upstream (within a given point bar) in simple meander bends. However, the presence of geomorphic complexities (e.g. cut banks connected to an incised channel or tributary and/or channel confinement) can challenge the unbiased quantification of the contribution of a single geomorphic variable to the observed lateral displacements. These findings can be applied to other fluvial environments outside of New Zealand, and the proposed framework can be implemented for other non-fluvial depositional settings. }, number={4}, journal={EARTHQUAKE SPECTRA}, author={Abayo, Nancy Ingabire and Cabas, Ashly and Chamberlin, Ellen and Montoya, Brina}, year={2023}, month={Nov}, pages={2518–2547} }
 @article{shahriar_gabr_montoya_ortiz_2023, title={Framework for a reliability-based analysis of local scour and its effect on pile response in clay}, volume={153}, ISSN={0266-352X}, url={http://dx.doi.org/10.1016/j.compgeo.2022.105093}, DOI={10.1016/j.compgeo.2022.105093}, abstractNote={The analyses of axial and lateral capacity of a pile are significantly dependent on the appropriate estimation of scour depth, while the scour depth estimation procedure is uncertain due to the hydraulic, hydrologic, and geotechnical parameters uncertainty. Work herein is focused on developing a framework for reliability-based pier scour assessment methodology and demonstrate its integration with the concept of Load and Resistance Factor Design (LRFD) approach. Scour factors are proposed based on reliability level ( β ) and the associated probability of deceedance (POD). Three example applications of axially and laterally loaded pile design approach while including scour factor in the LRFD framework are demonstrated. Based on axial pile capacity analysis, the increase of pile length when the β -based scour assessment is used with the soil resistance factors, was estimated to be 26.5–29.6 % higher compared to using the deterministic scour with soil resistance factor. In the case of lateral pile response analysis, as β is increased from 2.0 to 3.0, the lateral pile head deflection increased by 46–132 % compared to the deterministically-estimated scour depth case. To obtain β = 3.0 for the considered example while maintaining the pile length unchanged, the pile diameter needed to be increased by 35.7 % compared to the base case pile’s diameter.}, journal={Computers and Geotechnics}, publisher={Elsevier BV}, author={Shahriar, Azmayeen R. and Gabr, Mohammed A. and Montoya, Brina M. and Ortiz, Alejandra C.}, year={2023}, month={Jan}, pages={105093} }
 @book{rathje_montoya_wayne_2023, place={Reston, VA}, title={Geo-Congress 2023: Geotechnical Characterization}, ISBN={9780784484678}, DOI={10.1061/9780784484678}, abstractNote={Selected papers from sessions of Geo-Congress 2023, held in Los Angeles, California, March 26–29, 2023. Sponsored by the Geo-Institute of ASCE.}, publisher={American Society of Civil Engineers}, year={2023} }
 @book{rathje_montoya_wayne_2023, place={Reston, VA}, title={Geo-Congress 2023: Geotechnics of Natural Hazards}, ISBN={9780784484654}, DOI={10.1061/9780784484654}, publisher={American Society of Civil Engineers}, year={2023}, month={Mar} }
 @article{shahriar_gabr_montoya_ortiz_2023, title={Local scour around bridge abutments: Assessment of accuracy and conservatism}, volume={619}, ISSN={["1879-2707"]}, url={https://doi.org/10.1016/j.jhydrol.2023.129280}, DOI={10.1016/j.jhydrol.2023.129280}, abstractNote={More than 80 percent of the bridges in the United States are built over waterways. The support systems of the structures crossing waterways are subjected to scour during their service life owing to the flowing water-induced bed shear stresses, resulting in scour. Work herein is focused on characterizing the error associated with three abutment scour prediction models included in the Hydraulic Engineering Circular No. 18. An abutment scour database is utilized to quantify the predicted versus the measured scour depth relationship. Abutment scour prediction models are assessed in terms of two statistical parameters, termed herein Mean Absolute Percentage Error (MAPE, as a measure of accuracy of the prediction), and Level of conservatism, (defined as percentage of cases for which the predicted scour exceeded the measured scour.) For scour associated with vertical wall and spill through abutments, responses to long abutment, and intermediate abutment are examined separately. For vertical wall abutments, conservatism ranged from 4.76% to 100%, and MAPE ranged from 44% to 201%. For spill through abutments, conservatism ranged from 0% to 100%, and MAPE ranged from 10.3% to 347%. Comprehension of the accuracy and conservatism of the deterministic models considered herein contributes to understanding the limitation of the scour depth prediction models.}, journal={JOURNAL OF HYDROLOGY}, author={Shahriar, Azmayeen R. and Gabr, Mohammed A. and Montoya, Brina M. and Ortiz, Alejandra C.}, year={2023}, month={Apr} }
 @article{na_cabas_montoya_2023, title={Resonant Column Testing Procedure for Microbial-Induced Carbonate- Precipitated Sands}, volume={1}, ISSN={["1945-7545"]}, DOI={10.1520/GTJ20220056}, abstractNote={Abstract}, journal={GEOTECHNICAL TESTING JOURNAL}, author={Na, Kyunguk and Cabas, Ashly and Montoya, Brina M.}, year={2023}, month={Jan} }
 @article{faeli_montoya_gabr_2023, title={Various Bacterial Attachment Functions and Modeling of Biomass Distribution in MICP Implementations}, volume={149}, ISSN={["1943-5606"]}, url={https://doi.org/10.1061/JGGEFK.GTENG-10812}, DOI={10.1061/JGGEFK.GTENG-10812}, abstractNote={Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (CaCO3) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and “cstr based on colloid attachment theory”) were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted CaCO3 distribution compared with the experimental data. A new parameter, cstr, was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a 0.14×sample size. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of “the cstr based on colloid attachment theory” (hereafter “colloid attachment cstr”) as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume.}, number={9}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Faeli, Zahra and Montoya, Brina M. and Gabr, Mohammed A.}, year={2023}, month={Sep} }
 @article{ghasemi_montoya_2022, title={Effect of Treatment Solution Chemistry and Soil Engineering Properties due to Microbially Induced Carbonate Precipitation Treatments on Vegetation Health and Growth}, ISSN={["2690-0645"]}, DOI={10.1021/acsestengg.2c00196}, abstractNote={Microbially induced carbonate precipitation (MICP) is a soil stabilization technique that relies on natural biological processes to improve engineering properties of soil. This biological soil improvement method has gained popularity over the last decade. However, the unanticipated consequences of this method on vegetation and the environment are still unclear. This study presents the first attempt to strategically investigate the interaction between the MICP-treatment technique and vegetation health and growth. Bermuda grass was treated with different concentrations of MICP solution constituents and byproducts to identify the chemical(s) responsible for changes in plant health (e.g., dry blades) and to establish an appropriate concentration range. In addition, phosphorus was added to the treatment solution to mitigate the dryness of MICP-treated plants. Visual MINTEQ analyses were used to determine the optimum phosphorus concentration to still encourage sufficient calcite precipitation. Elemental analyses were used to confirm the compatibility of the added phosphorus concentrations with MICP. Post-treatment effect of MICP on seed growth was investigated by planting seeds in soils treated to varying cementation levels. Up to a certain improvement level, cementation formation did not affect seed germination and growth. However, higher levels of cementation hindered root growth and vegetation coverage. The findings of this study provide implications and directions regarding vegetation growth and establishment for future field implementation of MICP.}, journal={ACS ES&T ENGINEERING}, author={Ghasemi, Pegah and Montoya, Brina M.}, year={2022}, month={Oct} }
 @article{liu_montoya_2022, title={Effects of microbially induced carbonate precipitation on diffuse double layer and particle fabric of oil sands fine tailings}, ISSN={["1208-6029"]}, DOI={10.1139/cjce-2021-0240}, abstractNote={ Microbially induced carbonate precipitation (MICP) is a sustainable biological process that catalyzes carbonate mineral precipitation within geomaterials. This study evaluates the performance and mechanisms of the MICP treatment for flocculating the oil sands fine tailings (FT). Column tests showed that the untreated FT did not decant during the 31 days. However, the MICP technique shortened the dewatering process. To elucidate the mechanisms of the MICP-induced flocculation of the FT, the diffuse double layer (DDL) thickness and microstructure of the specimens were evaluated. Three chemical equilibrium scenarios that gradually considered the MICP-biochemical reactions were explored to analyze the change of the DDL thickness. The results showed that increasing of ionic strength by urea hydrolysis decreased the DDL thickness. The fabric observation indicated that the specimens with the most calcium carbonate precipitation had the densest fabric. In summary, the MICP technique densified the fabric of FT via the ureolysis process and precipitating minerals. }, journal={CANADIAN JOURNAL OF CIVIL ENGINEERING}, author={Liu, Qianwen and Montoya, Brina M.}, year={2022}, month={Jan} }
 @article{ghasemi_montoya_2022, title={Field Implementation of Microbially Induced Calcium Carbonate Precipitation for Surface Erosion Reduction of a Coastal Plain Sandy Slope}, volume={148}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002836}, abstractNote={Over the past decade, several researchers have demonstrated that microbially induced carbonate precipitation (MICP) has the potential to improve soil behavior in the laboratory setting. In this study, MICP was implemented at a sandy slope field site to enhance erosion resistance and surficial soil strength. Three application systems—surface spraying, prefabricated vertical drains (PVDs), and shallow trenches—were compared. Improvement of the treated soil was assessed using dynamic cone penetration, impinging jet, and pocket penetrometer tests and was monitored for 331 days. Results indicated that MICP is an effective soil improvement method for surficial and deeper applications. Penetration index values improved up to 73% and 55% at the surface and a depth of 30 cm, respectively. Critical shear stress and coefficient of erodibility values exhibited significant improvements. The surface spraying method is preferred for the treatment of large surficial areas, whereas the PVD method demonstrated deep soil improvement potential. The shallow trenches resulted in significant surficial improvements, however, in a highly localized manner. Post-treatment monitoring indicated no significant degradation of the treated areas with time and after major storm events (e.g., Hurricane Dorian). Based on the field results, a sensitivity analysis was performed to address the applicability of future MICP-field implementations in various soil types.}, number={9}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Ghasemi, Pegah and Montoya, Brina M.}, year={2022}, month={Sep} }
 @article{jadid_montoya_gabr_2022, title={Framework for the Development of Strain-Based Ultimate Performance Limit State Criterion for the Stability of Earthen Embankments}, volume={148}, ISSN={["1943-5606"]}, url={https://doi.org/10.1061/(ASCE)GT.1943-5606.0002754}, DOI={10.1061/(ASCE)GT.1943-5606.0002754}, abstractNote={Repeated rapid drawdown (RDD) and rapid rise in water level during extreme events lead to the progressive development of plastic strain zones within the earth embankments with subtle, rather than obvious, visible signs of distress. The traditional approach within the framework of limit equilibrium does not account for accumulated permanent deformation with repeated hydraulic loading. Work presented herein is focused on quantifying the level of deviatoric strain, in terms of key surface deformation and distress level of earth embankment slopes, with repeated hydraulic loading. A simple linear relationship between the deviatoric strain and surface deformation at the toe of the slip surface is proposed as a function of the geometry of the slope for rotational sliding. This relationship is applied using the stress-strain data obtained from conventional triaxial testing and provides a simple means to estimate the ultimate performance limit state that corresponds to the onset of embankment slope instability. Results from a parametric study show good agreement between the numerical results and proposed analytical criterion. The proposed criterion is also compared with data from field cases reported in literature by others, and reasonably good agreement with onset of failure is obtained. Results from applying the proposed model to the case studies indicate the applicability of the proposed approach as a framework for various loading conditions, slope geometries, and material properties.}, number={4}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, publisher={American Society of Civil Engineers (ASCE)}, author={Jadid, Rowshon and Montoya, Brina M. and Gabr, Mohammed}, year={2022}, month={Apr} }
 @article{shahriar_ortiz_montoya_gabr_2021, title={Bridge Pier Scour: An overview of factors affecting the phenomenon and comparative evaluation of selected models}, volume={28}, ISSN={2214-3912}, url={http://dx.doi.org/10.1016/j.trgeo.2021.100549}, DOI={10.1016/j.trgeo.2021.100549}, abstractNote={Scour, defined by the loss of geomaterials surrounding a foundation support system, is a primary cause of bridge failure in the United States and worldwide. Work herein presents a comprehensive review of the current state of knowledge on geotechnical aspects of erodibility, factors influencing pier scour, factors complicating pier scour assessment, and databases available on erodibility and pier scour. A summary of deterministic pier scour models, developed since 1990, is presented in view of the factors affecting scour rate and equilibrium magnitude. The study discusses challenges in the predictive approaches reviewed in the paper. In addition, advancements in probabilistic pier scour models, and observation-based models are summarized. Four pier scour models, namely Wilson (1995) model, Melville (1997) model, Hydraulic Engineering Circular No. 18 (2012) model, and Briaud (2014) model are comparatively applied to data from laboratory pier scour database. Error statistics and accuracy, precision, and probabilistic distribution of predictions from these models are presented and discussed.}, journal={Transportation Geotechnics}, publisher={Elsevier BV}, author={Shahriar, Azmayeen R. and Ortiz, Alejandra C. and Montoya, Brina M. and Gabr, Mohammed A.}, year={2021}, month={May}, pages={100549} }
 @article{montoya_do_gabr_2021, title={Distribution and Properties of Microbially Induced Carbonate Precipitation in Underwater Sand Bed}, volume={147}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002607}, abstractNote={AbstractMicrobially induced carbonate precipitation (MICP) is an innovative approach to strengthening and improving loose porous media. To advance MICP implementation in various geotechnical applic...}, number={10}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Montoya, Brina M. and Do, Jinung and Gabr, Mohammed A.}, year={2021}, month={Oct} }
 @article{nafisi_liu_montoya_2021, title={Effect of stress path on the shear response of bio-cemented sands}, ISSN={["1861-1133"]}, DOI={10.1007/s11440-021-01286-7}, journal={ACTA GEOTECHNICA}, author={Nafisi, Ashkan and Liu, Qianwen and Montoya, Brina M.}, year={2021}, month={Jun} }
 @article{liu_montoya_2021, title={Microbial-Induced Calcium Carbonate Precipitation to Accelerate Sedimentation of Fine Tailings}, volume={147}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002651}, number={10}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Liu, Qianwen and Montoya, Brina M.}, year={2021}, month={Oct} }
 @article{shahriar_montoya_ortiz_gabr_2021, title={Quantifying probability of deceedance estimates of clear water local scour around bridge piers}, volume={597}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/j.jhydrol.2021.126177}, DOI={10.1016/j.jhydrol.2021.126177}, abstractNote={Local bridge scour, which is defined as the loss of soil particles/mass surrounding a pier foundation due to the flowing water-induced shear stresses, is a primary cause of bridge failure in the United States and worldwide. Current practice of bridge scour prediction is mostly based on the use of deterministic models. Work herein presents statistical models that extend five deterministic approaches reported in literature to predict the expected scour depth while quantifying inherent model bias and uncertainty in view of data scatter. Clear water scour database is used herein and the analyses quantify model scatter by comparatively assessing the computed scour depth versus measured data reported in the database. A relationship between probability of deceedance associated with the predicted scour depth and a modification factor (that is applied into the deterministic prediction) is devised. The modification factor allows for the use of the scour magnitude computed from the deterministic models while quantifying the probability of a computed scour depth being less than or more than a most likely value (per measurements reported in the database). The application of the proposed model is demonstrated with an example and the results are discussed.}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Shahriar, Azmayeen R. and Montoya, Brina M. and Ortiz, Alejandra C. and Gabr, Mohammed A.}, year={2021}, month={Jun}, pages={126177} }
 @article{do_montoya_gabr_2021, title={Scour Mitigation and Erodibility Improvement Using Microbially Induced Carbonate Precipitation}, volume={44}, ISSN={["1945-7545"]}, DOI={10.1520/GTJ20190478}, abstractNote={Enhancing the scour resistance of foundation systems supporting superstructures over waterways is required for the sustainable functionality of the structure. In this article, the use of microbially induced carbonate precipitation (MICP) was investigated for the potential of its use in scour mitigation and erodibility improvement of sand. Testing was performed in a 0.91 by 1.22 by 1.22-m model box, and a double wall delivery system was developed and used to target cementation near the surface. A comparative study was performed on the scour behavior of untreated and treated samples using data from a series of flow tests. Impinging jet testing was used to evaluate the erodibility parameters of treated sand. The results from flow testing indicated that untreated and lightly cemented zones showed similar scour depth, whereas indiscernible scour was observed for the heavily cemented zone. The improvement distribution pattern throughout the media showed an ellipsoidal shape with respect to the injection source. The scour behavior and the cementation pattern indicated less cementation was achieved at the zone near the injection source because of high induced seepage velocity. Based on the impinging jet testing results, an empirical erosion model for MICP-treated sand is proposed as a function of the level of cementation.}, number={5}, journal={GEOTECHNICAL TESTING JOURNAL}, author={Do, Jinung and Montoya, Brina M. and Gabr, Mohammed A.}, year={2021}, month={Sep}, pages={1467–1483} }
 @article{jadid_montoya_bennett_gabr_2020, title={Effect of repeated rise and fall of water level on seepage-induced deformation and related stability analysis of Princeville levee}, volume={266}, ISSN={["1872-6917"]}, DOI={10.1016/j.enggeo.2019.105458}, abstractNote={The Princeville levee, and flooding associated with Hurricanes Floyd and Matthew, is used as a case study in which the analyses are focused on the effect of repeated rise and fall of water levels (representing severe storm cycles) on the stability of the levee and the risk of failure. The analyses included strain-based and strength reduction approaches and are conducted using the finite element program Plaxis 2D. The limit equilibrium stability software “Slope/W” was also used for comparative study. The strain-based limit state approach considers the uncertainty of soil properties and is used to characterize the levee performance under repeated storm loading in terms of damage levels (or limit states). The strain-based analyses results show a progressive development of plastic shear strain zone within the levee as the number of storm cycles is increased. The accumulation of such shear strain leads to increasing the probability of exceeding a given performance limit state. As more flooding cycles are introduced, the shear strain values increase by a factor of 3.5 from cycle 1 to 6, and therefore reflect the increasing level of failure risk. In parallel, the deterministic stability factor of safety obtained from limit equilibrium method remains unchanged and slightly changes for strength reduction method with an increased number of rises and falls of the water level. The consideration of “rapid” drawdown conventionally used in limit equilibrium stability analyses (where no consideration for time is included), instead of more realistic rate based on drawdown hydrograph leads to conservative estimate of factor of safety. The analyses results demonstrate the increase in risk with repeated hydraulic loading.}, journal={ENGINEERING GEOLOGY}, author={Jadid, Rowshon and Montoya, Brina M. and Bennett, Victoria and Gabr, Mohammed A.}, year={2020}, month={Mar} }
 @article{nafisi_montoya_evans_2020, title={Shear Strength Envelopes of Biocemented Sands with Varying Particle Size and Cementation Level}, volume={146}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002201}, abstractNote={AbstractMicrobial-induced calcium carbonate precipitation (MICP) is a bio-mediated technique that may be used to improve the strength and stiffness of soils. Various parameters affect the behavior ...}, number={3}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Nafisi, Ashkan and Montoya, Brina M. and Evans, T. Matthew}, year={2020}, month={Mar} }
 @article{nafisi_mocelin_montoya_underwood_2020, title={Tensile strength of sands treated with microbially induced carbonate precipitation}, volume={57}, ISSN={["1208-6010"]}, DOI={10.1139/cgj-2019-0230}, abstractNote={ During large earthquake events where bending moments within soil cements are induced, the tensile strength of cemented soil may govern the deformational behavior of improved ground. Several studies have been conducted to assess the tensile strength of artificially cemented sands that use Portland cement or gypsum; however, the tensile strength of microbially induced carbonate precipitation (MICP)-treated sands with various particle sizes measured through direct tension tests has not been evaluated. MICP is a biomediated improvement technique that binds soil particles through carbonate precipitation. In this study, the tensile strength of nine specimens were measured by conducting direct tension tests. Three types of sand (coarse, medium, and fine) were cemented to reach a heavy level of cementation (e.g., shear wave velocity of ∼900 m/s or higher). The results show that the tensile strength varies between 210 and 710 kPa depending on sand type and mass of carbonate. Unconfined compressive strength (UCS) tests were performed for each sand type to assess the ratio between tensile strength and UCS in MICP-treated sands. Scanning electron microscopy (SEM) images and surface energy measurements were used to determine the predominant failure mode at particle contacts under tensile loading condition. }, number={10}, journal={CANADIAN GEOTECHNICAL JOURNAL}, author={Nafisi, Ashkan and Mocelin, Douglas and Montoya, Brina M. and Underwood, Shane}, year={2020}, month={Oct}, pages={1611–1616} }
 @article{bozorgi_fried_montoya_castorena_2020, title={The effect of laboratory compaction method on the resilient behaviour and fabric of aggregate base course materials}, volume={21}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2019.1580606}, DOI={10.1080/14680629.2019.1580606}, abstractNote={Aggregate base course (ABC) layer is a key structural component of most pavements. The compaction of ABC is a crucial procedure affecting its mechanical performance. There are two different methods commonly used in the lab to compact ABC specimens: impact and vibratory. Past studies have demonstrated that the compaction method can affect the resilient deformation behaviour of ABC. However, the reasons for these differences in terms of the constituent ABC particle properties and the resultant compacted aggregate fabric remains unclear. This study evaluates the influence of the laboratory compaction method on the resilient behaviour and fabric of two ABC materials with differing mineralogies. Resilient modulus tests performed on the specimens compacted with the two methods result in different behaviours. A series of subsequent laboratory tests were performed to explain the observed resilient behaviour by assessing changes in aggregate morphology and fabric. The study presented herein incorporates digital imaging analyses using a novel specimen preparation technique. The results demonstrate that impact compaction can degrade ABC materials that are susceptible to crushing. This, in turn, increases the resilient modulus of the ABC by increasing the number of contact points between particles. It is recommended that the compaction method used in the laboratory match the compaction processes in the field as best as possible to obtain the most representative resilient modulus test results.}, number={7}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Bozorgi, A. and Fried, A. and Montoya, B.M. and Castorena, C.}, year={2020}, pages={1955–1967} }
 @article{do_montoya_gabr_2019, title={Debonding of microbially induced carbonate precipitation-stabilized sand by shearing and erosion}, volume={17}, ISSN={["2005-307X"]}, DOI={10.12989/gae.2019.17.5.429}, abstractNote={Microbially induced carbonate precipitation (MICP) is an innovative soil improvement approach utilizing metabolic activity of microbes to hydrolyze urea. In this paper, the shear response and the erodibility of MICP-treated sand under axial compression and submerged impinging jet were evaluated at a low confining stress range. Loose, poorly graded silica sand was used in testing. Specimens were cemented at low confining stresses until target shear wave velocities were achieved. Results indicated that the erodibility parameters of cemented specimens showed an increase in the critical shear stress by up to three orders of magnitude, while the erodibility coefficient decreased by up to four orders of magnitude. Such a trend was observed to be dependent on the level of cementation. The treated sand showed dilative behavior while the untreated sands showed contractive behavior. The shear modulus as a function of strain level, based on monitored shear wave velocity, indicated mineral debonding may commence at 0.05% axial strain. The peak strength was enhanced in terms of emerging cohesion parameter based on utilizing the Mohr-Coulomb failure criteria.}, number={5}, journal={GEOMECHANICS AND ENGINEERING}, author={Do, Jinung and Montoya, Brina M. and Gabr, Mohammed A.}, year={2019}, month={Apr}, pages={429–438} }
 @article{montoya_safavizadeh_gabr_2019, title={Enhancement of Coal Ash Compressibility Parameters Using Microbial-Induced Carbonate Precipitation}, volume={145}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.19435606.0002036}, number={5}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Montoya, Brina M. and Safavizadeh, Shahin and Gabr, Mohammed A.}, year={2019}, month={May} }
 @article{montoya_safavizadeh_gabr_2019, title={Enhancement of Coal Ash Compressibility Parameters Using Microbial-Induced Carbonate Precipitation}, volume={145}, ISSN={1090-0241 1943-5606}, url={http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0002036}, DOI={10.1061/(ASCE)GT.1943-5606.0002036}, abstractNote={AbstractMicrobial-induced calcium carbonate precipitation (MICP) was experimentally implemented on two coal ash materials (i.e., CA1 and CA3) to investigate the efficacy of the treatment on the hyd...}, number={5}, journal={Journal of Geotechnical and Geoenvironmental Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Montoya, Brina M. and Safavizadeh, Shahin and Gabr, Mohammed A.}, year={2019}, month={May}, pages={04019018} }
 @article{nafisi_safavizadeh_montoya_2019, title={Influence of Microbe and Enzyme-Induced Treatments on Cemented Sand Shear Response}, volume={145}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002111}, abstractNote={AbstractMicrobial-induced calcium carbonate precipitation (MICP) and enzyme-induced calcium carbonate precipitation (EICP) are both soil improvement techniques that improve the shear response of sa...}, number={9}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Nafisi, Ashkan and Safavizadeh, Shahin and Montoya, Brina M.}, year={2019}, month={Sep} }
 @article{zamani_montoya_gabr_2019, title={Investigating challenges of in situ delivery of microbial-induced calcium carbonate precipitation (MICP) in fine-grain sands and silty sand}, volume={56}, ISSN={0008-3674 1208-6010}, url={http://dx.doi.org/10.1139/cgj-2018-0551}, DOI={10.1139/cgj-2018-0551}, abstractNote={ Microbial-induced calcium carbonate precipitation (MICP) is a sustainable soil improvement method with the potential for improving the engineering properties of sand and silty soils and therefore their resistance to liquefaction-inducing events. Work presented herein experimentally investigates the changes in hydraulic conductivity of fine sands and silty sands as a result of MICP treatment. In addition, numerical modeling is conducted to assess the changes in allowable injection rate and radius of influence for the delivery of the MICP process at the field scale. The hydraulic conductivity of Nevada sand and silty sand with 15% fines content decreased through MICP application with the trend of reduction being similar for both soils. Numerical modeling results show that with the progress of the MICP process, injection rates can be increased for Nevada sand, but remain unchanged for Nevada sand with 15% silt content (after MICP treatment up to a shear wave velocity about 400 m/s.) The presence of fines by itself leads to generation of higher levels of pore-water pressure during the injection process, which necessitates higher strength improvement to prevent development of excessive plastic strains. Therefore, improvement in shear strength and stiffness relative to the magnitude of the hydraulic conductivity level and its rate of change during the MICP process is a key parameter in determining the radius of treatment. }, number={12}, journal={Canadian Geotechnical Journal}, publisher={Canadian Science Publishing}, author={Zamani, A. and Montoya, B.M. and Gabr, M.A.}, year={2019}, month={Dec}, pages={1889–1900} }
 @inproceedings{nafisi_montoya_2019, title={MICP}, ISBN={9780784482117}, url={http://dx.doi.org/10.1061/9780784482117.020}, DOI={10.1061/9780784482117.020}, booktitle={Geo-Congress 2019}, publisher={American Society of Civil Engineers}, author={Nafisi, Ashkan and Montoya, Brina M.}, year={2019}, month={Mar} }
 @inproceedings{ghasemi_zamani_montoya_2019, title={MICP}, ISBN={9780784482117}, url={http://dx.doi.org/10.1061/9780784482117.024}, DOI={10.1061/9780784482117.024}, abstractNote={Sandy slopes supporting coastal roadways are susceptible to failure during large storm events due to erosion and slope stability. Investigating the application of a natural and sustainable soil improvement method is required to increase the shear strength and erosion resistance of sands while having less impact on the coastal ecology. Microbial induced calcium carbonate precipitation (MICP) is a novel and promising soil improvement technique that utilizes indigenous soil bacteria to hydrolyze urea and induce calcium carbonate precipitation, which improves the mechanical properties of the soil. The chemical concentrations and recipe ratios used for this process can affect the level of improvement. This study aims to draw a relationship between the chemical ratios, shear strength, and erodibility resistance of MICP treated sands. In an attempt to tailor the laboratory experiments closer to field requirements, industrial grade chemicals were used to treat the soil specimens. A submerged impinging jet system was used to evaluate the erodibility parameters of soil specimens treated with different ratios of urea to calcium chloride. Unconfined compression strength tests (UCS), an indication of shear strength, were performed on specimens with similar properties treated with different ratios of urea to calcium chloride. Shear wave velocity measurements were used to detect the level of improvement in all soil specimens during the treatment. The results indicate that the ratio of urea to calcium chloride can affect the number of treatments required to reach a target level of improvement. In addition, the ratio of chemical concentrations can change the erosion strength differently compared to the UCS. These results can also provide a basis for choosing an optimum treatment recipe for field application, by keeping a balance between the mechanical properties of MICP treated soils, mass of calcium carbonate, and cost of chemicals used for treatment.}, booktitle={Geo-Congress 2019}, publisher={American Society of Civil Engineers}, author={Ghasemi, Pegah and Zamani, Atefeh and Montoya, Brina}, year={2019}, month={Mar} }
 @inproceedings{do_montoya_gabr_2019, title={MICP}, ISBN={9780784482117}, url={http://dx.doi.org/10.1061/9780784482117.028}, DOI={10.1061/9780784482117.028}, abstractNote={In this study, injection configuration system to stabilize soil mass around a pile foundation with the microbially induced carbonate precipitation was developed and a simplified scheme for field implementation was proposed using seepage and chemical transport analysis. Experimental testing included a tracer experiment in a large-scale soil box with the results used to calibrate transport parameters for the numerical model. Results indicated that the use of a central injection through the pile lead to effective distribution of the tracer within the flow domain. The radius of the zone of influence was estimated as 8.5D based on the induced flow hydraulic gradient of 0.7. Target concentration was used as a design criterion to determine the injection duration. Analyses indicated 7.5 days of injection duration was needed to affect a zone having 4D extent with a tracer concentration of 100%. Recommendations are presented regarding volume treatment scenarios with the use of single point injections.}, booktitle={Geo-Congress 2019}, publisher={American Society of Civil Engineers}, author={Do, Jinung and Montoya, Brina M. and Gabr, Mohammed A.}, year={2019}, month={Mar} }
 @article{safavizadeh_montoya_gabr_2019, title={Microbial induced calcium carbonate precipitation in coal ash}, volume={69}, ISSN={0016-8505 1751-7656}, url={http://dx.doi.org/10.1680/jgeot.18.P.062}, DOI={10.1680/jgeot.18.P.062}, abstractNote={ The long-term storage of coal ash in impoundments can lead to concerns of structural stability as well as trace element migration to local surface water and groundwater sources. Microbial induced calcium carbonate precipitation (MICP) offers a potential approach for minimising leachability of heavy metal trace elements from coal ash by calcium carbonate cementation. In this study, a protocol for MICP treatment of coal ash has been experimentally developed. The MICP treatment is applied to three coal ashes from different power plants, and their response to the developed treatment protocol is assessed. Possible factors affecting the MICP treatment of coal ash are discussed in terms of efficacey and inhibition of the stabilisation process. For this purpose, several approaches such as shear wave velocity, electrical conductivity, pH measurement, acid washing, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were implemented. The results indicated that carbon/carbide content of the fly ash material has an important role in the efficacey of the MICP treatment process. The most likely explanation is carbon/carbide aids in the nucleation of calcium carbonate precipitation. }, number={8}, journal={Géotechnique}, publisher={Thomas Telford Ltd.}, author={Safavizadeh, Shahin and Montoya, Brina M. and Gabr, Mohammed A.}, year={2019}, month={Aug}, pages={727–740} }
 @article{zamani_montoya_2019, title={Undrained cyclic response of silty sands improved by microbial induced calcium carbonate precipitation}, volume={120}, ISSN={["1879-341X"]}, DOI={10.1016/j.soildyn.2019.01.010}, abstractNote={Loose saturated silty sand can be prone to liquefaction but improving their soil properties is challenging due to their lower permeability compared to clean sands. Microbial induced calcium carbonate precipitation (MICP) is a new, natural and sustainable soil improvement method, which can increase the shear strength and stiffness of soils. In this study, MICP treatment is applied to silty sands with fines content in the range of 0–35% and a constant preshear void ratio 0.7 ± 0.05 to observe improvement in their liquefaction resistance. The specimens are treated until reaching a shear wave velocity about 400 m/s. Cyclic direct simple shear testing is used to evaluate changes in the liquefaction resistance of untreated and MICP treated silty sands. The results show that by applying MICP the liquefaction resistance increases significantly for all fines contents tested, and the treatment efficiency depends on the level of fines content, which dictate the relative density, and the fabric governing the structure. As examples, the 35% fines content specimen has shown the highest improvement, which is related to a higher relative density at this fines content. The silty sand specimens with 5% fines content has a metastable structure which makes the soil more sensitive to cyclic loading. Although the cyclic resistance has increased by applying MICP at this level of fines content, its sensitivity to cyclic loading has remained unchanged. The results of this study demonstrate that MICP improves the cyclic strength of silty sand and can provide an alternative soil improvement method for silty sand.}, journal={SOIL DYNAMICS AND EARTHQUAKE ENGINEERING}, author={Zamani, Atefeh and Montoya, Brina M.}, year={2019}, month={May}, pages={436–448} }
 @inproceedings{nafisi_montoya_2018, title={A new framework for identifying cementation level of MICP-treated sands}, url={http://www.lib.ncsu.edu/resolver/1840.20/36315}, DOI={10.1061/9780784481592.005}, abstractNote={Microbial induced calcium carbonate precipitation (MICP) is a ground improvement technique that can be employed to increase soil stiffness and shear strength. Based on the treatment’s objectives, soil properties are improved to reach different levels of cementation. Shear wave velocity and mass of calcium carbonate can be used to categorize treated soils into various levels of cementation. However, the obtained results show that these two parameters are not sufficient in categorizing cementation and may be misleading. Therefore, a new framework which considers particle size, the dependency of shear modulus on confinement, shear wave velocity, and calcium carbonate content is proposed. In this paper, three types of poorly graded sands with different particle sizes were used. Shear modulus was measured at varying levels of cementation and confinement pressures to find out the amount of dependency of small strain shear modulus on confining pressure. According to the results, the finest soil needs more calcium carbonate to reach heavily cemented level, but the final shear wave velocity is lower compared to the coarser sands. Based on the obtained results, n (the slope of log Gmax against log of mean effective stress) values for lightly, moderately, and heavily MICP-sands are about 0.4, 0.3, and less than 0.1, respectively.}, note={annote: Nafisi, A., & Montoya, B. M. (2018). A new framework for identifying cementation level of MICP-treated sands. In Ifcee 2018: innovations in ground improvement for soils, pavements, and subgrades (pp. 37–47).}, number={296}, booktitle={Ifcee 2018: innovations in ground improvement for soils, pavements, and subgrades}, author={Nafisi, A. and Montoya, B.M.}, year={2018}, pages={37–47} }
 @article{montoya_2018, title={Editorial}, volume={5}, ISSN={["2051-803X"]}, DOI={10.1680/jenge.2018.5.2.67}, abstractNote={Biological processes, associated with microbes and root structures alike, are prevalent throughout the geoenvironment and have the potential to transform soil fabric and behavior.Harnessing these bio-geo processes in soil can lead to more sustainable approaches to meet societies ever-evolving needs.The papers presented within this themed issue, the bio-geo interface, aim at deepening our understanding of how biological processes effect the engineering properties of soil and the performance of geotechnical systems.}, number={2}, journal={ENVIRONMENTAL GEOTECHNICS}, author={Montoya, Brina M.}, year={2018}, month={Apr}, pages={67–68} }
 @inproceedings{safavizadeh_montoya_gabr_2018, title={Effect of Microbial Induced Calcium Carbonate Precipitation on Compressibility and Hydraulic Conductivity of Fly Ash}, url={http://dx.doi.org/10.1061/9780784481592.008}, DOI={10.1061/9780784481592.008}, abstractNote={The morphology and chemical composition of fly ash render the material unique in comparison to natural sediments. Fly ash deposited in ash ponds can possess a loose, saturated, and contractive structure with a tendency to collapse under induced shear stresses. Compressibility and hydraulic conductivity are the two main parameters affecting the stability of this material in ash ponds. Microbial induced calcium carbonate precipitation (MICP) is a novel approach, which has been widely studied to improve engineering properties of soils. In this study, the MICP treatment process is applied to a Class-F fly ash material to assess its effect on the two mentioned parameters. Modified odometer testing was developed with the ability to inject the treatment solution, measure the induced pressure during injection, and monitor the shear wave velocity of the test specimens. The specimens were successfully treated using MICP, reaching predetermined target shear wave velocities. The results of compressibility on treated and untreated specimens indicate that MICP decreases the compressibility of the studied material while the hydraulic conductivity decreased by only one order of magnitude or less. The shear wave velocity of the treated and untreated specimens converged to the same value while the vertical applied stress increased, indicating the calcium carbonate bond breakage between particles.}, number={296}, booktitle={IFCEE 2018}, publisher={American Society of Civil Engineers}, author={Safavizadeh, Shahin and Montoya, Brina M. and Gabr, Mohammed A.}, year={2018}, month={Jun}, pages={69–79} }
 @inproceedings{zamani_liu_montoya_2018, title={Effect of microbial induced carbonate precipitation on the stability of mine tailings}, DOI={10.1061/9780784481615.024}, abstractNote={Dams and impoundments are the most conventional method for depositing mine tailings material. Regular operation of the tailings dams often increase the height of the dams, which may make them susceptible to failure. Many existing mine tailings dams are prone to slope failure and require remediation. In this study, microbial induced calcium carbonate precipitation (MICP) is presented as a new method to improve the stability of mine tailings dams against slope failure. MICP also has the potential to improve other deficiencies of the mine tailings material such as surface erosion, static liquefaction, and dynamic liquefaction. In the present study, Slope/W program is used to perform slope stability analysis and observe the effect of MICP on the static slope stability of mine tailings material. The results show an increase in the slope stability after biocementation. The level of improvement in the factor of safety against slope failure depends on the level of treatment.}, number={298}, booktitle={Ifcee 2018: case histories and lessons learned}, author={Zamani, A. and Liu, Q. W. and Montoya, B. M.}, year={2018}, pages={291–300} }
 @misc{montoya_do_gabr_2018, title={Erodibility of Microbial Induced Carbonate Precipitation-Stabilized Sand under Submerged Impinging Jet}, url={http://dx.doi.org/10.1061/9780784481592.003}, DOI={10.1061/9780784481592.003}, abstractNote={Scour adjacent to foundation systems is a contributing factor to significant structural damage. Microbial induced carbonate precipitation (MICP) is investigated as an approach to improve the soil’s shear strength and stiffness and reduce the potential to scour. In this study, a submerged impinging jet system (mini JET apparatus) is used to assess the erodibility of MICP-treated sand with results presented in the context of data in literature. The results indicated that the critical shear stresses of the MICP-treated specimens increased one to three orders of magnitude, while the erodibility coefficients decreased by up to four orders of magnitude as the cementation level increases. The micro image analysis confirmed that cementation is achieved via precipitated calcium carbonate at the particle contacts. These results suggest that moderate to high levels of cementation using the MICP process is potentially an effective approach to reduce the sand’s erodibility.}, number={296}, journal={IFCEE 2018}, publisher={American Society of Civil Engineers}, author={Montoya, Brina M. and Do, Jinung and Gabr, Mohammed M.}, year={2018}, month={Jun}, pages={19–28} }
 @inproceedings{zamani_feng_montoya_2018, title={Liquefaction Triggering, Consequences, and Mitigation}, ISBN={9780784481455}, url={http://dx.doi.org/10.1061/9780784481455.029}, DOI={10.1061/9780784481455.029}, abstractNote={Microbial induced calcium carbonate precipitation (MICP) has been shown to be an effective method to improve soil strength and stiffness, and one of the most promising applications of MICP is for liquefaction mitigation. In this paper, three silica soils with varying grain sizes were treated by MICP to a moderate level of cementation and their resistance to liquefaction is improved significantly compared to uncemented loose soil. The degree of MICP improvement appears to be influenced by the grain size and shape of the loose untreated soil. The level of excess pore water and cyclic resistance of the untreated and MICP treated soils is presented. The different response to cyclic loading after MICP treatment is compared with respect to different grain size and shape. The results show that reduction in grain size and increase in angularity result in a higher resistance to liquefaction after MICP treatment.}, booktitle={Geotechnical Earthquake Engineering and Soil Dynamics V}, publisher={American Society of Civil Engineers}, author={Zamani, A. and Feng, K. and Montoya, B. M.}, year={2018}, month={Jun} }
 @article{safavizadeh_montoya_gabr_2018, title={Treating Coal Ash with Microbial-Induced Calcium Carbonate Precipitation}, volume={144}, ISSN={1090-0241 1943-5606}, url={http://dx.doi.org/10.1061/(asce)gt.1943-5606.0001956}, DOI={10.1061/(asce)gt.1943-5606.0001956}, number={11}, journal={Journal of Geotechnical and Geoenvironmental Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Safavizadeh, S. and Montoya, B. M. and Gabr, M. A.}, year={2018}, month={Nov}, pages={02818003} }
 @article{zamani_montoya_2018, title={Undrained Monotonic Shear Response of MICP-Treated Silty Sands}, volume={144}, ISSN={["1943-5606"]}, DOI={10.1061/(asce)gt.1943-5606.0001861}, abstractNote={AbstractThe effect of nonplastic fines on the undrained shear response of sand depends on many variables, including fines content, skeleton void ratio (es), interfine void ratio (ef), global void r...}, number={6}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Zamani, A. and Montoya, B. M.}, year={2018}, month={Jun} }
 @article{feng_montoya_evans_2017, title={Discrete element method simulations of bio-cemented sands}, volume={85}, ISSN={["1873-7633"]}, DOI={10.1016/j.compgeo.2016.12.028}, abstractNote={Microbially induced calcite precipitation (MICP) has emerged as a novel soil improvement method. In this paper, 3-D discrete element method (DEM) simulations are used to explore the behavior of MICP-cemented sands. Comparisons of the macro-scale response of numerical and physical specimens are made. Microstructure analyses indicate a shear band formed in the numerical specimens, consistent with physical experiments. The bond breakage pattern in numerical specimens is explored and compared to observed measurements from physical specimens. The relationship between dilatancy and stress-strain behavior is evaluated. The results indicate DEM is an effective technique to capture the mechanical behavior of MICP-cemented sand.}, journal={COMPUTERS AND GEOTECHNICS}, author={Feng, Kai and Montoya, B. M. and Evans, T. M.}, year={2017}, month={May}, pages={139–150} }
 @article{feng_montoya_2017, title={Quantifying Level of Microbial-Induced Cementation for Cyclically Loaded Sand}, volume={143}, ISSN={["1943-5606"]}, DOI={10.1061/(asce)gt.1943-5606.0001682}, abstractNote={AbstractMicrobial-induced calcite precipitation (MICP) is a novel soil-improvement technique that improves the behavior of sands subjected to dynamic loading. The level of cementation of MICP-treat...}, number={6}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Feng, Kai and Montoya, Brina M.}, year={2017}, month={Jun} }
 @inproceedings{zamani_montoya_2017, title={Shearing and Hydraulic Behavior of MICP Treated Silty Sand}, ISBN={9780784480489}, url={http://dx.doi.org/10.1061/9780784480489.029}, DOI={10.1061/9780784480489.029}, abstractNote={Microbial induced calcite precipitation (MICP) is a biochemical reaction that takes place within the soil producing calcite cementation bonding soil grains together. In this study, MICP method was applied to both Nevada sand and Nevada sand containing 15% silt to assess their improvement in monotonic shear strength, cyclic resistance and also changes in permeability. The change in shear strength properties are evaluated by performing undrained monotonic and cyclic direct simple shear tests on both treated and untreated samples. Reduction in permeability as a result of calcite precipitation is also another objective of this research which is investigated by performing constant head tests on untreated and MICP treated samples. The results show improvement in shear response and reduction in excess pore water pressure in both treated samples. The cyclic resistance also increases by applying MICP. The permeability of soil reduces by applying MICP but the amount of reduction is low in comparison to the change in permeability when fines are added to the Nevada sand.}, booktitle={Geotechnical Frontiers 2017}, publisher={American Society of Civil Engineers}, author={Zamani, Atefeh and Montoya, Brina M.}, year={2017}, month={Mar} }
 @inproceedings{shanahan_montoya_2016, title={Erosion Reduction of Coastal Sands Using Microbial Induced Calcite Precipitation}, ISBN={9780784480120}, url={http://dx.doi.org/10.1061/9780784480120.006}, DOI={10.1061/9780784480120.006}, abstractNote={Effects of sea level rising and increasing storm severity create a more damage prone environment for coastal regions. Large storm surges can be devastating to coastal infrastructure, damaging roads, utilities, structures, and endangering the lives of local residents. Coastal sand dunes act as a primary defense to wave action, making their resiliency of the utmost importance. Microbial induced calcite precipitation (MICP) offers a potentially sustainable alternative to seawall and revetment type solutions which destroy entire ecosystems in order to protect cities or other areas of interest. Bio-cementation has been shown to improve the strength and stiffness of unsaturated sand. The study presented herein displays the behavior of MICP treated coastal sand when subjected to wave action. Two wave tank tests were conducted to assess the change in measured erosion for untreated sand and moderately cemented sand. To quantitatively measure the reduction in erosion, 3-D morphology was observed using a laser scanner before and after subjecting the sand to wave action. Acoustic wave gauges were used to monitor the input wave functions and the breaking waves on the soil surface. Further understanding of the erosion reduction potential of MICP treated sand increases the feasibility of in-situ application to coastal sand dunes.}, booktitle={Geo-Chicago 2016}, publisher={American Society of Civil Engineers}, author={Shanahan, Casey and Montoya, Brina M.}, year={2016}, month={Aug} }
 @article{feng_montoya_2016, title={Influence of Confinement and Cementation Level on the Behavior of Microbial-Induced Calcite Precipitated Sands under Monotonic Drained Loading}, volume={142}, ISSN={["1943-5606"]}, DOI={10.1061/(asce)gt.1943-5606.0001379}, abstractNote={AbstractMicrobial-induced calcite precipitation (MICP) is a novel ground improvement method to increase strength and stiffness of sand using natural biogeochemical processes. Cementation level and confining pressure are two important factors that control the behavior of MICP sand. The monotonic mechanical response of MICP cemented sand is systematically investigated using four cementation levels (untreated, lightly treated, moderately treated, and heavily treated) and three levels of effective confining pressure (100, 200, and 400 kPa). The results indicate that the stiffness, peak shear strength, and dilation increases with an increase in calcite content at a given effective confining pressure and the dilation is suppressed with an increase in effective confining pressure. This behavior is consistent with soil-like behavior; therefore, all the MICP soils presented herein are evaluated using critical-state soil mechanics and not an analogous fracture-mechanics framework. The experimental results also indi...}, number={1}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Feng, K. and Montoya, B. M.}, year={2016}, month={Jan} }
 @inproceedings{khoubani_evans_montoya_2016, title={Particulate Simulations of Triaxial Tests on Bio-Cemented Sand Using a New Cementation Model}, ISBN={9780784480120}, url={http://dx.doi.org/10.1061/9780784480120.010}, DOI={10.1061/9780784480120.010}, abstractNote={Bio-cementation is a promising method for the natural improvement of potentially liquefiable soil deposits (e.g., loose saturated sands). In the improvement process a bacterium that can be found naturally in soil deposits is fed urea. The bacterium consumes and breaks down the urea to form ammonium and carbonate. In the presence of calcium, calcium carbonate will precipitate at particle contacts and act as a cementitious agent to solidify the deposit. Moreover, experimental tests show that bio-cemented sand exhibits more ductile behavior than chemically cemented sand. This is a desirable response from an engineering point of view, since brittle failure is often catastrophic and occurs without warning. The scope of this study is to investigate the response of bio-cemented sand using the discrete element method (DEM). This numerical method is capable of simulating behavior of granular materials based upon the basic particle-scale physics of the system of interest. A new cementation model is proposed that replicates the presence of cement between soil particles. This bond is able to capture the progressive contact dissolution between two soil particles and associated nonlinear response. Triaxial samples were built and the aforementioned bond was applied to the contact points within the assembly. Samples with and without cementation are sheared and their stress-strain responses compared in terms of soil strength and stiffness. The effects of several bonding parameters are investigated and the relative contributions of multiple physical mechanisms to system response are considered.}, booktitle={Geo-Chicago 2016}, publisher={American Society of Civil Engineers}, author={Khoubani, A. and Evans, T. M. and Montoya, B. M.}, year={2016}, month={Aug} }
 @inproceedings{zamani_montoya_2016, title={Permeability Reduction Due to Microbial Induced Calcite Precipitation in Sand}, ISBN={9780784480120}, url={http://dx.doi.org/10.1061/9780784480120.011}, DOI={10.1061/9780784480120.011}, abstractNote={Fine sands have shown that they are susceptible to liquefaction. There are many soil improvement methods that are effective in improving the shear strength and stiffness of fine sand but they often have limitations due to the soil characteristics, such as permeability. Microbial induced calcite precipitation (MICP) has been shown to be a natural and effective liquefaction mitigation method for clean fine sands. Although this method is effective, there may be limitations in implementing MICP in situ. In this study, the permeability reduction from MICP is investigated to understand its implications for field implementation of MICP treatments. Fine sand specimens have been treated to different cementation levels, estimated using nondestructive shear wave velocity measurements. Permeability of treated samples is measured using a constant head permeameter. Utilizing the permeability results of the treated specimens, numerical simulations of the MICP treatments are evaluated by creating a constant head difference between an injection and extraction well and observing the water velocity changes within the domain.}, booktitle={Geo-Chicago 2016}, publisher={American Society of Civil Engineers}, author={Zamani, Atefeh and Montoya, Brina M.}, year={2016}, month={Aug} }
 @inproceedings{montoya_safavizadeh_meredith_2016, title={The Use of Microbial Induced Calcite Precipitation to Reduce Trace Element Leaching from Fly Ash}, ISBN={9780784480144}, url={http://dx.doi.org/10.1061/9780784480144.098}, DOI={10.1061/9780784480144.098}, abstractNote={North Carolina has recently been facing issues associated with the storage of coal ash, specifically preventing trace elements found in coal ash from leaching into the local groundwater. The research program presented herein focuses on reducing the leachability of trace elements found in coal ash using bio-mediated methods. Microbial induced calcite precipitation (MICP) is used to immobilize trace elements within the fly ash. The MICP process is initiated within ponded fly ash material set up in soil columns, and effluent is collected from the treated fly ash material. The concentrations of the trace elements are measured using inductively coupled plasma mass spectrometry (ICP-MS). The concentrations within the MICP-treated fly ash effluent are compared to baseline fly ash effluent. The MICP treatment process is also applied to dry fly ash material that may be used within construction projects. The MICP treatment process was applied to fly ash material in a similar manner as moisture conditioning during compaction. The MICP treatment process was allowed to take place, then effluent samples were collected from percolating water. The MICP-treated leachate was compared to that of a baseline compacted fly ash sample and compared to the results from the ponded fly ash.}, number={271}, booktitle={Geo-Chicago 2016}, publisher={American Society of Civil Engineers}, author={Montoya, Brina M. and Safavizadeh, Shahin and Meredith, Ashley}, year={2016}, month={Aug}, pages={989–997} }
 @inproceedings{montoya_feng_2015, title={Deformation of microbial induced calcite bonded sands: A micro-scale investigation}, volume={6}, booktitle={Deformation characteristics of geomaterials}, author={Montoya, B. and Feng, K.}, year={2015}, pages={978–985} }
 @inproceedings{feng_montoya_2015, title={Drained Shear Strength of MICP Sand at Varying Cementation Levels}, ISBN={9780784479087}, url={http://dx.doi.org/10.1061/9780784479087.208}, DOI={10.1061/9780784479087.208}, abstractNote={Microbial induced calcite precipitation (MICP) is a novel ground improvement method to increase strength and stiffness of sand using natural biogeochemical processes. Cementation level and confining pressure are two important factors that control the behavior of MICP sand. The static mechanical responses of MICP Cemented Sand are systematically investigated using four cementation levels (untreated, lightly treated, moderately treated, and heavily treated) and three levels of confining pressure (100kPa, 200kPa, and 400kPa). The experimental results indicate that the improvement in shear strength parameters is dependent on the level of cementation under peak and residual states. Uniformity of MICP cementation in laboratory scale is also discussed. When comparing the response of MICP sand with naturally cemented sand and artificially treated sand with Portland cement, the MICP cemented sand is observed to better capture the small strain stiffness of the naturally cemented soil.}, booktitle={IFCEE 2015}, publisher={American Society of Civil Engineers}, author={Feng, K. and Montoya, B. M.}, year={2015}, month={Mar} }
 @inproceedings{evans_khoubani_montoya_2015, title={Simulating mechanical response in bio-cemented sands}, booktitle={Computer Methods and Recent Advances in Geomechanics}, author={Evans, T. M. and Khoubani, A. and Montoya, B. M.}, year={2015}, pages={1569–1574} }
 @article{montoya_dejong_2015, title={Stress-Strain Behavior of Sands Cemented by Microbially Induced Calcite Precipitation}, volume={141}, ISSN={["1943-5606"]}, DOI={10.1061/(asce)gt.1943-5606.0001302}, abstractNote={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 ...}, number={6}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Montoya, B. M. and DeJong, J. T.}, year={2015}, month={Jun} }
 @inproceedings{feng_montoya_2014, title={Behavior of Bio-Mediated Soil ink0Loading}, ISBN={9780784413456}, url={http://dx.doi.org/10.1061/9780784413456.001}, DOI={10.1061/9780784413456.001}, abstractNote={Microbial induced carbonate precipitation is a novel soil improvement method that has demonstrated potential to strengthen the ground in a sustainable and eco-friendly manner. Previous investigations have studied its mechanical behavior through conventional triaxial or soil column tests. However, there is limited information about the bio-cemented sand's properties under k0 loading, which more closely resembles some in situ stress conditions. Using a modified consolidation cell with shear wave velocity monitoring via bender elements, the authors investigate the behavior of bio-treated sand under loading and unloading. The effects of cementation degree(shear wave velocity 350 m/s and 700 m/s after cementation) and initial densities(loose and dense) are explored through careful preparation of samples. The results of the bio-cemented specimens under an incremental loading and unloading sequence are compared to that of uncemented sand at similar densities.}, booktitle={New Frontiers in Geotechnical Engineering}, publisher={American Society of Civil Engineers}, author={Feng, K. and Montoya, B. M.}, year={2014}, month={May} }
 @article{bernardi_dejong_montoya_martinez_2014, title={Bio-bricks: Biologically cemented sandstone bricks}, volume={55}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2014.01.019}, abstractNote={The cementation of sand into sandstone through microbial activity is a novel technology with a wide range of possible applications. The cementation process involves the introduction of bacteria and nutrients to sand, and through bacterial processes calcite precipitation binds particles together, ultimately creating a sandstone material. This technology could provide a new, more sustainable building material in the form of “bio-bricks”. This paper describes the treatment technique as well as results from testing after brick manufacturing. Bricks were tested to determine compression (p-wave) wave velocity, unconfined compression strength, and calcite concentration. P-wave velocity, stiffness, strength, and calcite content of bio-bricks all increase with further treatment of bacteria and cementation media. Results show that bio-bricks can have strengths ranging from 1 MPa to 2 MPa. Bio-bricks are comparable in terms of stress and stiffness to bricks prepared with the more conventional cement and hydraulic lime additives.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Bernardi, D. and DeJong, J. T. and Montoya, B. M. and Martinez, B. C.}, year={2014}, month={Mar}, pages={462–469} }
 @inproceedings{feng_montoya_evans_2014, title={Numerical Investigation of Microbial-Induced Cemented Sand Mechanical Behavior}, ISBN={9780784413272}, url={http://dx.doi.org/10.1061/9780784413272.161}, DOI={10.1061/9780784413272.161}, abstractNote={Microbial induced carbonate precipitation (MICP) has been proven to be an effective method to stabilize problem soils using natural biological processes. Previous triaxial tests show the stiffness and strength of loose sand can be increased significantly by bio-cementation under drained and undrained conditions. Modeling using the discrete element method (DEM) provides a means to evaluate the micromechanics of sands and bond structure degradation during shearing, which are not easily captured in physical experiments. After calibrating with stress-strain behavior observed from microbial induced cemented sands in physical tests, a numerical model is used to explore the mechanical response of microbial induced cemented sands under varying loading and unloading stress paths.}, booktitle={Geo-Congress 2014 Technical Papers}, publisher={American Society of Civil Engineers}, author={Feng, K. and Montoya, B. M. and Evans, T. M.}, year={2014}, month={Feb} }
 @inproceedings{shanahan_montoya_2014, title={Strengthening Coastal Sand Dunes Using Microbial-Induced Calcite Precipitation}, ISBN={9780784413272}, url={http://dx.doi.org/10.1061/9780784413272.165}, DOI={10.1061/9780784413272.165}, abstractNote={In the event of large storms, coastal regions are particularly vulnerable. The effect of erosion on coastal soils can be devastating, and may result in damage to structures, roadways, and utilities. This damage can be extremely costly and may result in serious harm. Previous work has shown that the strength and stiffness of loose, saturated sand increases by utilizing microbial induced carbonate precipitation (MICP). The work presented herein applies the MICP treatment process to sandy coastal soil in order to increase its resistance to erosion. Utilizing the MICP treatment technique in unsaturated soils, rigid-wall soil column tests were conducted. The soil tested was clean fine sand, typical of coastal dune deposits. The soil remained unsaturated by allowing free drainage during treatments. Shear strength was measured through unconfined compression testing. By upscaling the treatment process, a bench model simulating a costal sand dune was tested to determine the change in the angle of repose for the MICP treated soil and its increase in erosion resistance. Erosion due to wave action was assessed by comparing the behavior of an untreated model sand dune to a MICP treated model sand dune subjected to simulated waves.}, booktitle={Geo-Congress 2014 Technical Papers}, publisher={American Society of Civil Engineers}, author={Shanahan, C. and Montoya, B. M.}, year={2014}, month={Feb} }
 @article{dejong_soga_kavazanjian_burns_van paassen_al qabany_aydilek_bang_burbank_caslake_et al._2013, title={Biogeochemical processes and geotechnical applications: progress, opportunities and challenges}, volume={63}, ISSN={["1751-7656"]}, DOI={10.1680/geot.sip13.p.017}, abstractNote={ Consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers. }, number={4}, journal={GEOTECHNIQUE}, author={Dejong, J. T. and Soga, K. and Kavazanjian, E. and Burns, S. E. and Van Paassen, L. A. and Al Qabany, A. and Aydilek, A. and Bang, S. S. and Burbank, M. and Caslake, L. F. and et al.}, year={2013}, month={Mar}, pages={287–301} }
 @article{montoya_dejong_boulanger_2013, title={Dynamic response of liquefiable sand improved by microbial-induced calcite precipitation}, volume={63}, ISSN={["1751-7656"]}, DOI={10.1680/geot.sip13.p.019}, abstractNote={ Microbial-induced calcite precipitation (MICP), a novel bio-mediated ground improvement method, was explored to mitigate liquefaction-prone soils. Geotechnical centrifuge tests were used to evaluate cementation integrity and the response of MICP cemented sands to dynamic loading. The cementation integrity testing reveals a change in behaviour from ‘soil like' to ‘rock like', with an increase in treatment level. Results from dynamic testing demonstrate a clear increase in resistance to liquefaction of MICP-treated sands compared to untreated loose sand. The MICP sands were treated to varying levels of cementation (light, moderate and heavy cementation levels) and assessed using non-destructive shear wave velocity measurements. The centrifuge models were all subjected to ground motions consisting of sine waves with increasing amplitudes. Accelerations, pore pressures and settlements were measured in the soil during shaking, and the changes in soil behaviour and post-shaking shear wave velocity for soils prepared to different cementation levels are discussed. Increased resistance to liquefaction was demonstrated with a decrease in excess pore pressure ratios in the MICP-treated models, as well as in reduced post-shaking settlements; however, surface accelerations were amplified at heavy levels of cementation. A tradeoff between improving liquefaction resistance and minimising undesirable higher surface accelerations needs to be considered when designing the soil improvement level. }, number={4}, journal={GEOTECHNIQUE}, author={Montoya, B. M. and Dejong, J. T. and Boulanger, R. W.}, year={2013}, month={Mar}, pages={302–312} }
 @article{martinez_dejong_ginn_montoya_barkouki_hunt_tanyu_major_2013, title={Experimental Optimization of Microbial-Induced Carbonate Precipitation for Soil Improvement}, volume={139}, ISSN={["1943-5606"]}, DOI={10.1061/(asce)gt.1943-5606.0000787}, abstractNote={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...}, number={4}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Martinez, B. C. and DeJong, J. T. and Ginn, T. R. and Montoya, B. M. and Barkouki, T. H. and Hunt, C. and Tanyu, B. and Major, D.}, year={2013}, month={Apr}, pages={587–598} }
 @article{montoya_dejong_2013, title={Healing of biologically induced cemented sands}, volume={3}, ISSN={["2045-2543"]}, DOI={10.1680/geolett.13.00044}, abstractNote={ Microbial-induced calcite precipitation (MICP) is a novel bio-mediated ground improvement method that can be used to increase the shear strength and stiffness of sand. One of the benefits of the MICP treatment process is the ability to heal degraded calcite bonds post-shearing. The healed bonds can then improve the sand properties (small strain stiffness and peak strength) compared with those of the pre-shearing condition. The MICP healing process was evaluated using monotonic undrained shearing and dynamic centrifuge tests, and comparing the sand behaviour before and after the healing process. Similar or improved behaviour was observed after the healing process. This healing ability implies that degraded MICP-treated sands can be healed after loading (e.g. in an earthquake) to their original level of treatment to prevent additional settlements or damage from subsequent loading (e.g. aftershocks). }, journal={GEOTECHNIQUE LETTERS}, author={Montoya, B. M. and Dejong, J. T.}, year={2013}, pages={147–151} }
 @article{montoya_gerhard_dejong_wilson_weil_martinez_pederson_2012, title={Fabrication, operation, and health monitoring of bender elements for aggressive environments}, volume={35}, DOI={10.1520/gtj103300}, abstractNote={Abstract}, number={5}, journal={Geotechnical Testing Journal}, author={Montoya, B. M. and Gerhard, R. and DeJong, J. T. and Wilson, D. W. and Weil, M. H. and Martinez, B. C. and Pederson, L.}, year={2012}, pages={728–742} }
 @inproceedings{montoya_dejong_boulanger_wilson_gerhard_ganchenko_chou_2012, title={Liquefaction Mitigation Using Microbial Induced Calcite Precipitation}, ISBN={9780784412121}, url={http://dx.doi.org/10.1061/9780784412121.197}, DOI={10.1061/9780784412121.197}, abstractNote={The potential of a novel, bio-mediated soil improvement to increase resistance to liquefaction triggering and to reduce the consequences of liquefaction if it occurs was evaluated. Microbial induced calcite precipitation (MICP) binds sand particles together through calcite crystal formation at particle-particle contacts. This results in an increase in the small-strain stiffness and strength of treated loose sand. Geotechnical centrifuge tests were used to evaluate the increased resistance of MICP treated sand relative to untreated loose sand when subjected to seismic shaking. Results of one model with a structure founded on sand treated to a moderate level of cementation and another model with the structure founded on loose untreated sand are compared. The centrifuge models were subjected to ground motions consisting of sine waves with increasing amplitudes. The accelerations, pore pressures, and shear wave velocities measured in the soil during shaking are presented. The resistance to liquefaction and deformation in the MICP treated model showed significant increases, as evidenced by substantial decreases in excess pore pressure ratios and vertical strains beneath the structure.}, booktitle={GeoCongress 2012}, publisher={American Society of Civil Engineers}, author={Montoya, B.M. and DeJong, J.T. and Boulanger, Ross W. and Wilson, Dan W. and Gerhard, Ray and Ganchenko, Anatoliy and Chou, Jui-Ching}, year={2012}, month={Mar} }
 @article{weil_dejong_martinez_mortensen_2012, title={Seismic and Resistivity Measurements for Real-Time Monitoring of Microbially Induced Calcite Precipitation in Sand}, volume={35}, ISSN={0149-6115}, url={http://dx.doi.org/10.1520/gtj103365}, DOI={10.1520/gtj103365}, abstractNote={Abstract}, number={2}, journal={Geotechnical Testing Journal}, publisher={ASTM International}, author={Weil, Matthew H. and DeJong, Jason T. and Martinez, Brian C. and Mortensen, Brina M.}, year={2012}, pages={330–341} }
 @article{mortensen_haber_dejong_caslake_nelson_2011, title={Effects of environmental factors on microbial induced calcium carbonate precipitation}, volume={111}, ISSN={1364-5072}, url={http://dx.doi.org/10.1111/j.1365-2672.2011.05065.x}, DOI={10.1111/j.1365-2672.2011.05065.x}, abstractNote={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.}, number={2}, journal={Journal of Applied Microbiology}, publisher={Wiley}, author={Mortensen, B.M. and Haber, M.J. and DeJong, J.T. and Caslake, L.F. and Nelson, D.C.}, year={2011}, month={Jun}, pages={338–349} }
 @article{barkouki_martinez_mortensen_weathers_de jong_ginn_spycher_smith_fujita_2011, title={Forward and Inverse Bio-Geochemical Modeling of Microbially Induced Calcite Precipitation in Half-Meter Column Experiments}, volume={90}, ISSN={0169-3913 1573-1634}, url={http://dx.doi.org/10.1007/s11242-011-9804-z}, DOI={10.1007/s11242-011-9804-z}, number={1}, journal={Transport in Porous Media}, publisher={Springer Science and Business Media LLC}, author={Barkouki, T. H. and Martinez, B. C. and Mortensen, B. M. and Weathers, T. S. and De Jong, J. D. and Ginn, T. R. and Spycher, N. F. and Smith, R. W. and Fujita, Y.}, year={2011}, month={Aug}, pages={23–39} }
 @article{dejong_soga_banwart_whalley_ginn_nelson_mortensen_martinez_barkouki_2011, title={Soil engineering in vivo : harnessing natural biogeochemical systems for sustainable, multi-functional engineering solutions}, volume={8}, ISSN={1742-5689 1742-5662}, url={http://dx.doi.org/10.1098/rsif.2010.0270}, DOI={10.1098/rsif.2010.0270}, abstractNote={
            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.
          }, number={54}, journal={Journal of The Royal Society Interface}, publisher={The Royal Society}, author={DeJong, Jason T. and Soga, Kenichi and Banwart, Steven A. and Whalley, W. Richard and Ginn, Timothy R. and Nelson, Douglas C. and Mortensen, Brina M. and Martinez, Brian C. and Barkouki, Tammer}, year={2011}, month={Jan}, pages={1–15} }
 @article{dejong_mortensen_martinez_nelson_2010, title={Bio-mediated soil improvement}, volume={36}, ISSN={0925-8574}, url={http://dx.doi.org/10.1016/j.ecoleng.2008.12.029}, DOI={10.1016/j.ecoleng.2008.12.029}, abstractNote={New, exciting opportunities for utilizing biological processes to modify the engineering properties of the subsurface (e.g. strength, stiffness, permeability) have recently emerged. Enabled by interdisciplinary research at the confluence of microbiology, geochemistry, and civil engineering, this new field has the potential to meet society's ever-expanding needs for innovative treatment processes that improve soil supporting new and existing infrastructure. This paper first presents an overview of bio-mediated improvement systems, identifying the primary components and interplay between different disciplines. Geometric compatibility between soil and microbes that restricts the utility of different systems is identified. Focus is then narrowed to a specific system, namely bio-mediated calcite precipitation of sands. Following an overview of the process, alternative biological processes for inducing calcite precipitation are identified and various microscopy techniques are used to assess how the pore space volume is altered by calcite precipitation, the calcite precipitation is distributed spatially within the pore space, and the precipitated calcite degrades during loading. Non-destructive geophysical process monitoring techniques are described and their utility explored. Next, the extent to which various soil engineering properties is identified through experimental examples. Potential advantages and envisioned applications of bio-mediated soil improvement are identified. Finally, the primary challenges that lie ahead, namely optimization and upscaling of the processes and the education/training of researchers/practitioners are briefly discussed.}, number={2}, journal={Ecological Engineering}, publisher={Elsevier BV}, author={DeJong, Jason T. and Mortensen, Brina M. and Martinez, Brian C. and Nelson, Douglas C.}, year={2010}, month={Feb}, pages={197–210} }