Microstructural and geo-mechanical study on bio-cemented sand for optimization of MICP process

Limited research has been reported on strength improvement of biocemented soils in relation to crystal patterns of microbially induced calcite (CaCO3) precipitation (MICP). In this study, sand samples were treated under the coeffect of different bacterial culture (BC) and cementation solution (CS) concentrations to evaluate the optimum BC and CS combination that yields the highest soil strength. It was found that for lower CS conditions (0.25 M), higher BC produced stronger samples, whereas for higher CS conditions (0.5 M or 1 M), lower BC was more dominant in improving the soil strength. This can be attributed to the effectively precipitated CaCO3 crystals, which were in rhombohedral shape and large size and were concentrated at the soil pore throat rather than deposited on the individual sand grain surface. This finding was confirmed with the scanning electron microscopy (SEM) analysis. The strength and permeability of the optimized biocemented samples were also compared with sand samples treated with ordinary portland cement (OPC). The optimized biocemented sand provided higher strength and permeability than those obtained from the samples treated with similar content of OPC at a curing period of 28 days

Numerical Modelling of the Consolidation Behavior of Peat Soil Improved by Sand Columns

This paper presents a ground improvement method using sand as material in columnar inclusion. The main focus of the study is to model the consolidation behavior of peat soil reinforced by sand columns. The effects of sand column length and column diameter were determined using numerical analysis. It was revealed that the final settlement strongly depends on the area replacement ratio. The numerical results showed that the installation of larger-diameter, fully penetrated columns reduced soil settlement. The settlement reduction results of our numerical analysis are in good agreement with the experimental results. In order to improve the confining stresses of sand, an alternative approach utilizing geogrid encasement was examined numerically. The increasing stiffness of geogrid effectively increased the load carrying capacity of the sand column. Based on the results, geogrid performs better in smaller-diameter columns

Performance evaluation of the soft soil reinforced ground palm oil fuel ash layer composite

© 2015 Elsevier Ltd. All rights reserved. This study seeks to validate the possible reuse of the ground palm oil fuel ash (POFA) in soft soil improvement. POFA used in the present study was derived from the abundantly available palm oil waste residues from the nearby palm oil mill. Once the POFA is dried, it is further grounded to two different particle sizes i.e. 30 µm (large particle) and 12 µm sieve (small particle) in order to determine the effect of the POFA fineness in soft soil improvement. Furthermore, a one dimensional deformation analysis was carried out using the oedometer apparatus to investigate the effect of water saturation in soft soil samples incorporating both the original unground POFA. The result showed that the improvement factor portrayed by the smaller particle size of the ground POFA was much more pronounced as compared to the larger particle size. Similar trend was found in the consolidation results especially when the soft soil sample was fully saturated. Also, the shear strength parameters of the reinforced soft soil with ground POFA increased significantly at about 50%-60% for both the internal friction angle and the cohesion values

Evaluation of the mechanical properties of recycled glass fibers-derived three dimensional geomaterial for ground improvement

This research was aimed to study the potential use of recycled glass fibers-derived three dimensionalgeomaterial (8FG MAT) obtained from industrial glass fiber wastes to innovate a sustainable, costeffective geosynthetic for ground improvement in problematic soil applications. The ready availability, high tensile strength, lightweight and non-biodegradable characteristics of glass fibers further elevate their advantages as compared to the presently adopted geosynthetics in soft soil reinforcement condition. In this study, mechanical properties of recycled glass fibers and their ‘8’ shape form samples as well as the pullout resistance force of 8FG MAT were investigated by considering glass fibers’ layer thickness, shape formation and orientation in a laboratory scale model. It was observed that the tensile and yield strengths of overall geomaterial samples significantly increase as strip layers thickness increase. Results from both the tensile strength and pullout resistance force indicated similar trend of increasing in strength values with test conducted using other type of geosynthetics in various soil media to simulate the action of different soil conditions at real sites