Microbial induced calcite precipitation treatment on tropical residual soil

Biomediated soil improvement, also known as Microbial Induced Calcite Precipitation (MICP), is a promising new branch of microbial geotechnology. Earlier MICP studies only focused on sandy soils, but more recent studies have also investigated the potential and feasibility of MICP on tropical residual soil. The main objective of this study is to examine the feasibility of MICP and the mechanisms involved between two types of bacteria and chemical reagents in improving the strength of tropical residual soil. Essentially, this was about identifying the optimized treatment conditions as well as the effects of some specific MICP parameters and curing on unconfined compressive strength (UCS) development and calcite distribution. Two bacteria from the Bacillus family, namely, Bacillus subtilis and Sporosarcina pasteurii, were used as urease producing bacteria. The tropical residual silt soil with 80% fine soil was compressed to a cylindrical sample measuring 100 mm in height and 50 mm in diameter as well as having a dry density of 1.31 Mg/m3. Continuous injection method was employed. Series of tests were carried out, with each having different chemical reagents concentrations (0.15, 0.25, 0.35 or 0.45 M), reagent flow pressures (0.1, 0.2, 0.3 or 0.4 bars), and treatment durations (24, 48, 72 or 96 hours). Strength improvement of about 56.70% and 38.14% was immediately discovered after MICP treatment using Sporosarcina pasteurii and Bacillus subtilis, respectively. Additionally, strength improvement of about 30 to 104.12% were recorded after curing the samples for 3, 7, 14, 20, and 28 days. The optimum curing period was 14 days. The optimum treatment condition of MICP treatment for both bacteria consisted of 0.25 M of reagent concentration, 0.2 bars of reagent flow pressure, and 48 hours of treatment duration. The reagent flow pressure was the only MICP parameter that affected calcite distribution. No clear correlation was observed between calcite precipitation and strength. The two bacteria had distinctive responses to the designated treatment conditions as the behaviour of living microorganisms could differ although they are from the same family. This information were analysed to establish design charts for MICP practitioner in selecting optimal MICP parameters under different circumstances

Static response on lime column and geotextile encapsulated lime column (GELC) stabilised marine clay under vertical load

Marine clay, which is widely encountered in coastal area in Malaysia, is a problematic base material. Previous researchers reported that deep lime stabilisation can significantly improve clay. However, insufficient confining pressure from surrounding soil normally lead to the inferior performance on the upper part of column such as column head crushing and larger deformation on the surrounding soil at top part of column. Therefore, geotextile encapsulation was proposed for lime column in this study. Static response and stress distribution are essential in the understanding on behaviour of columnar stabilised soil under vertical load. Multi stages loading tests were conducted on Pontian marine clay, with and without geotextile encapsulation. Stress concentration ratio (smid/ ssoil) was examined in each loading stage, where it is defined as stress on column (smid) divided by stress on surrounding soil (ssoil). The samples were cured for 14, 28 and 56 days before tested. It was found that stress concentration ratio was dependent on column materials strength properties and applied loading. Geotextile encapsulation increased the stress concentration ratio on lime column. Stress concentration increment effect by geotextile encapsulation was further enhanced by the confining pressure of surrounding soil; however, the effect reduced with increase of applied loading. Higher stress concentration ratio indicated lesser load on surrounding soil and therefore the soil settlement could be reduced

Geochemistry characterization of organic soil

The behaviour of organic soil was found to be governed by its chemical properties rather than its physical properties. Hence, it is important to determine the geochemistry properties of organic soils besides its physical properties. The main objective of this study was to characterize the geochemistry properties of organic soils for civil engineering applications. The organic soil specimens were retrieved from three different locations at Batu Pahat, Johor, namely Parit Nipah, Parit Sidek and Batu Puteh using peat auger and undisturbed sampler. The top layer of the peat soil which is rich in non-humified matters was excluded from this study. The geochemistry properties of the organic soils underneath the peat soil were determined through laboratory tests; Total Organic Carbon (TOC), Loss of Ignition (LOI) and etc. Besides it, this study also highlighted the correlation of geochemistry properties of organic soils with its physical behaviors namely strength, moisture content, specific gravity, and Atterberg limits. This study provided a good understanding of organic soils which enable the designer to identify and investigate the effect of geochemical properties towards the soil behaviour

Biological process of soil improvement in civil engineering: A review

The concept of using biological process in soil improvement which is known as bio-mediated soil improvement technique has shown greater potential in geotechnical engineering applications in terms of performance and environmental sustainability. This paper presents a review on the soil microorganisms responsible for this process, and factors that affect their metabolic activities and geometric compatibility with the soil particle sizes. Two mechanisms of biomineralization, i.e. biologically controlled and biologically induced mineralization, were also discussed. Environmental and other factors that may be encountered in situ during microbially induced calcite precipitation (MICP) and their influences on the process were identified and presented. Improvements in the engineering properties of soil such as strength/stiffness and permeability as evaluated in some studies were explored. Potential applications of the process in geotechnical engineering and the challenges of field application of the process were identified

Effect of Geotextile Encapsulation on Lime Column Axial Stress in Pontain Marine Clay

Abstract. Previous researchers reported that problematic soft clay can be improved by deep lime stabilization. However, due to low confining pressure of surrounding soil, problems often occurred at top part of column which reduced the performance of lime column, such as: crushing at column head and higher settlement for surrounding soil at the upper part of column. Geotextile encapsulated lime column (GELC) was proposed in this study. The stresses on column are essential in the analysis on columnar improved soil. Multi-stage loading test was conducted on lime column and GELC stabilized Pontian marine clay aged 14 days, 28 days and 56 days in order to investigate axial stress on lime column and GELC stabilized Pontian marine clay. Geotextile encapsulation increased the compressive strength of lime column about 70 percent at axial strain of 8 percent

Effect of Geotextile Encapsulation on Lime Column Axial Stress in Pontain Marine Clay

Abstract. Previous researchers reported that problematic soft clay can be improved by deep lime stabilization. However, due to low confining pressure of surrounding soil, problems often occurred at top part of column which reduced the performance of lime column, such as: crushing at column head and higher settlement for surrounding soil at the upper part of column. Geotextile encapsulated lime column (GELC) was proposed in this study. The stresses on column are essential in the analysis on columnar improved soil. Multi-stage loading test was conducted on lime column and GELC stabilized Pontian marine clay aged 14 days, 28 days and 56 days in order to investigate axial stress on lime column and GELC stabilized Pontian marine clay. Geotextile encapsulation increased the compressive strength of lime column about 70 percent at axial strain of 8 percent