| Popis: |
ABSTRACT: Microbially induced calcite precipitation (MICP) is a ground improvement technique where the metabolic activities of bacteria are utilized to produce calcium carbonate precipitants at the grain contacts or within the pore spaces, enhancing bonding between the soil particles thus generating artificially cemented rocks with improved stiffness/strength properties. A key challenge in practical implementation of this technology is determining the percentage of the produced bio-cement and characterization of the resulting weakly consolidated rocks. Non-destructive techniques (NDT) are ideal for monitoring the percentage of the produced bio-cement, which is of a non-uniform and heterogenic nature, as well as the characteristics of the bio-induced cemented rock. In this study, we have conducted a series of controlled laboratory column tests where various bio-cemented samples were produced. NDT experiments including S-wave velocity measurements were taken along samples to determine bio-cementation and characterize the enhanced strength properties. Advanced signal processing techniques were conducted to interpret the findings. Results were compared against unconfined compressive tests (UCS). Findings provide a novel insight into utilization of NDT and interpretation of the results for charactering weakly consolidated rocks. 1. INTRODUCTION Microbiological-induced calcite precipitation (MICP) is a ground improvement technique that utilizes ureolytic microorganisms capable of hydrolyzing urea to generate calcium carbonate minerals, referred to as bio-cement (Stocks-Fisher et al. 1999). The resulting enhanced engineering properties in soils treated through MICP are governed by the distribution of bio-cement at the pore-scale, which is heterogeneous and complex in nature. When the produced bio-cement is precipitated at the soil particle contacts, it can enhance bonding between soil particles thus improve shear stiffness and shear strength, compressibility and dilatancy tendencies, and liquefaction resistance (e.g., DeJong et al., 2006; Martinez and DeJong, 2009; Montoya and DeJong 2015). The hydraulic characteristics of bio-treated soils however are found to be mainly impacted by the percentage of the bio-cement produced in the pores (pore filling). |
