{"683038":{"#nid":"683038","#data":{"type":"event","title":"PhD Defense by Shaivan Shivaprakash","body":[{"value":"\u003Cp\u003ESchool of Civil and Environmental Engineering\u003Cbr\u003E\u003Cbr\u003EPh.D. Thesis Defense Announcement\u003Cbr\u003E\u003Cbr\u003E\u003Cbr\u003EInfluence of Micro-scale Mechanisms on Macro-scale Properties of Bio-cemented Soils\u003Cbr\u003E\u003Cbr\u003EBy Shaivan Shivaprakash\u003Cbr\u003E\u003Cbr\u003EAdvisor:\u003Cbr\u003E\u003Cbr\u003EDr. Susan E. Burns\u003Cbr\u003E\u003Cbr\u003ECommittee Members: Dr. Sheng Dai (CEE), Dr. Xing Xie (CEE),\u003Cbr\u003EDr. David Frost (CEE), Dr. Yuanzhi Tang (EAS)\u003Cbr\u003E\u003Cbr\u003EDate and Time: July, 21, 2025. 11:00 \u2013 2:00 PM EST\u003Cbr\u003E\u003Cbr\u003ELocation: SEB 122\u003Cbr\u003E\u003Cbr\u003EDue to its versatile applications, microbially induced carbonate precipitation (MICP) via\u003Cbr\u003Eurea hydrolysis has gained considerable interest in diverse fields, ranging from soil sciences to\u003Cbr\u003Eapplied microbiology, to geomicrobiology to civil and environmental engineering. The objective\u003Cbr\u003Eof this thesis is to elucidate the role of micro-scale mechanisms on the macro-scale behavior of\u003Cbr\u003Ebio-cemented soils, and the overarching goal of this research is to address the growing need for\u003Cbr\u003Esustainable ground improvement techniques in geotechnical engineering.\u003Cbr\u003EA series of bench scale column experiments were performed to investigate the impacts of micro-scale factors on the implementation of MICP under a range of experimental conditions. The\u003Cbr\u003Escope of the MICP technique was expanded beyond traditionally tested silica sands to include the\u003Cbr\u003Ecarbonate-rich soils to improve the versatility and robustness of the technique, which showed that\u003Cbr\u003Ethe pre-existing carbonate soil particles served as preferential sites for calcite crystal growth due\u003Cbr\u003Eto their lower energy barrier compared to nucleation on silica particles. These findings were further\u003Cbr\u003Evalidated through MICP experiments on artificially graded carbonate-sand mixtures, where similar\u003Cbr\u003Ecalcite morphologies were observed on Iceland Spar (pure calcium carbonate) particles. A novel\u003Cbr\u003Eexperimental setup was introduced in this research to capture the effect of non-uniform\u003Cbr\u003Ecementation on the evolution of shear-wave velocity of the bio-cemented column. The testing\u003Cbr\u003Esetup successfully captured the spatial variation in Vs with treatment depth, as well as the average\u003Cbr\u003Estiffness of the entire bio-cemented column, overcoming the limitations of previous studies and\u003Cbr\u003Eprovided quantifiable improvements in geotechnical engineering properties with treatment depth\u003Cbr\u003Eas a result of bio-cementation.\u003Cbr\u003EAdditionally, micro-scale visualization performed on biologically preserved bio-cemented\u003Cbr\u003Especimens showed bacterial cells entombed within calcite crystals and serving as nucleation sites,\u003Cbr\u003Egrowth of individual bacterial cells and colonies predominantly near the precipitated calcite, and\u003Cbr\u003Eformation of bacterial chains connecting different calcite crystals together resulting in the\u003Cbr\u003Eformation of cementation bonds between soil particles. These findings provided direct evidence\u003Cbr\u003Efor key hypothesized mechanisms in the MICP process and offer a more comprehensive, holistic\u003Cbr\u003Eunderstanding of the physicochemical and biological interactions that drive soil bio-cementation. Micro-scale observations of precipitated calcite morphologies and cementation bonds\u003Cbr\u003Eacross all tested soils revealed three primary mechanisms responsible for increase in shear-wave\u003Cbr\u003Evelocity: contact cementation, particle-coating, and pore filling and matrix cementation. These\u003Cbr\u003Emechanisms were shown to be influenced by the physical properties of the soil, including particle\u003Cbr\u003Esize, shape, mineralogy, and specific surface area (SSA). Importantly, the traditional linear\u003Cbr\u003Erelationship between Vs and calcite content, widely used in the literature, failed to account for the\u003Cbr\u003Eobserved variability across these different soil types and morphology. To address this limitation,\u003Cbr\u003EVs was related to normalized calcite content, defined as calcite content divided by the specific\u003Cbr\u003Esurface area of the soil. The model demonstrated improved performance in capturing the variation\u003Cbr\u003Ein Vs across both the experimental dataset of this study and a broader literature dataset. This model\u003Cbr\u003Ewas found to be generalizable across a wide range of soils, including those with varying particle\u003Cbr\u003Esizes, mineralogy, and morphological characteristics, thereby providing a more robust framework\u003Cbr\u003Efor predicting the stiffness of bio-cemented soils during the MICP process.\u003C\/p\u003E","summary":"","format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003E\u003Cstrong\u003EInfluence of Micro-scale Mechanisms on Macro-scale Properties of Bio-cemented Soils\u003C\/strong\u003E\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Influence of Micro-scale Mechanisms on Macro-scale Properties of Bio-cemented Soils"}],"uid":"27707","created_gmt":"2025-07-08 15:19:12","changed_gmt":"2025-07-08 15:19:42","author":"Tatianna Richardson","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2025-07-21T11:00:00-04:00","event_time_end":"2025-07-21T14:00:00-04:00","event_time_end_last":"2025-07-21T14:00:00-04:00","gmt_time_start":"2025-07-21 15:00:00","gmt_time_end":"2025-07-21 18:00:00","gmt_time_end_last":"2025-07-21 18:00:00","rrule":null,"timezone":"America\/New_York"},"location":"SEB 122","extras":[],"groups":[{"id":"221981","name":"Graduate Studies"}],"categories":[],"keywords":[{"id":"100811","name":"Phd Defense"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[{"id":"1788","name":"Other\/Miscellaneous"}],"invited_audience":[{"id":"78771","name":"Public"}],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[],"email":[],"slides":[],"orientation":[],"userdata":""}}}