Sandy Soil Stabilization by Microbial Induced Calcite Precipitation (MICP) using Bio-stimulation Method

dc.contributor.advisor Jiang, Ningjun NJ Wang, Yijie
dc.contributor.department Civil Engineering 2022-07-05T19:58:19Z 2022-07-05T19:58:19Z 2022 Ph.D.
dc.subject Civil engineering
dc.subject Geotechnology
dc.subject Biogeochemistry
dc.subject bio-stimulation
dc.subject biochemical response
dc.subject calcareous sand
dc.subject erosion
dc.subject microbially induced calcite precipitation
dc.subject shearing behaviors
dc.title Sandy Soil Stabilization by Microbial Induced Calcite Precipitation (MICP) using Bio-stimulation Method
dc.type Thesis
dcterms.abstract Calcareous sands are often considered as very unstable and evolving materials with large particles allowing an abundance of air space. Their physical properties are usually defined as weak or no structure, free draining with high permeability, poor water retention, and high sensitivity to compaction. In tropic areas, the physical properties of sandy soils are more complicated. A more frequent cycling of wetting and drying can affect the physical properties significantly. These adverse engineering properties make it difficult to manage in the construction field. Chemical stabilization has been applied in the field for years. Frequently used stabilizers include Portland cement, lime and industrial waste lime, asphalt, and others. However, the major problem of these tradition materials is highly dependent on mass industrial production which requires substantial energy. Some potential environmental issues can be induced due to the high alkaline level of many of these chemical stabilizers. Considering the abovementioned limitations of those traditional additives, alternative technique is required to make the sandy soil stabilization more economic and environmental-friendly. Microbiologically Induced Calcite Precipitation (MICP) as a new interdisciplinary method combines the microbiological, geochemical, and geotechnical research to fulfill the increasing demands for the sandy soil improvement. The stabilization process can be achieved by inducing calcite precipitation within the sand matrix via microbial ureolysis procedure by ureolytic bacteria. The produced calcite precipitation preferentially accumulates at particle-particle contacts, which can provide extra connection and gain more strength. Because of the widely distribution of ureolytic microbes in the natural soil, the in-situ bio-stimulation of indigenous ureolytic bacteria becomes feasible. The study in this thesis firstly investigated the effect of enrichment media on the stimulation of native ureolytic bacteria in calcareous sand under solution condition. A series of batch tests were conducted, and the generic and three different selective enrichment media were compared from the biochemical aspects. The results show that the selective enrichment media rich in urea could successfully stimulate and enrich the native ureolytic bacteria by monitoring the ureolytic activity, pH, and electric conductivity. The nutrients with higher nitrogen sources show better efficiency in improving ureolytic activity. Secondly, the biochemical and direct shear behaviors of bio-cemented sand treated by bio-stimulated MICP were investigated under sand column condition. It was found that during the enrichment phase, the indigenous ureolytic bacteria can be enriched significantly within 48 hours, though the ureolysis rate was varying with the initial urea concentration. The microbial community changed significantly after enrichment stage. The ureolytic species could be found in the sand. Furthermore, the cementation content increased with the flushing number of cementation solution. The shear strength of bio-cemented sand could be significantly enhanced after MICP treatment. The cohesion and peak friction angle increased with elevated cementation level while declined with the increasing normal stress. Then, the compressive characteristics of bio-cemented sand was studied under one-dimensional compression tests. It was found that the compressibility of bio-cemented reduced with the increasing cementation content. The samples prepared under higher initial relative density showed less compression. Based on microscopic observations, a conceptual framework based on the interparticle contact modes and their corresponding damage modes during the compression tests was proposed. After that, to find out a way to preserve the enriched urease within soils as much as possible, and further increase the bio-cementation content, the biochar-amendment was incorporated into MICP. The shear behavior of biochar-amended bio-cemented calcareous sand treated via bio-stimulation was investigated through a series of direct shear test. The results showed that the addition of biochar powders could effectively increase the cementation content as the extra nucleation sites for native ureolytic bacteria. However, too much biochar within bio-cementation may become weak points and thus diminish the contribution of interparticle bonding to the shear strength. Finally, a preliminary exploration of bio-stimulated MICP in rainfall-induced erosion prevention was conducted by a series of laboratory model tests. The artificial sandy slope was made and subjected to the rainfall. Meanwhile, the photography-based SfM (Structure from Motion) as the new technique was firstly applied to evaluate the slope deformation under rainfall-induced erosion. The results showed that bio-stimulated MICP could significantly reduce the erosion on a sandy slope, especially in case treated by YE-based enrichment medium with 170 initial urea concentration. It is a good trial to explore a feasible monitoring way for the future full-scale application in field.
dcterms.extent 203 pages
dcterms.language en
dcterms.publisher University of Hawai'i at Manoa
dcterms.rights All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
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