바이오그라우팅공법의 주입재 배합비에 따른 적용성

Abstract

Recently, soft grounds and coastal areas have been steadily reclamated for more efficient use of lands and for increase of construction spaces. For the purpose, significant effort has been put to develop efficient ground improvement methods on soft grounds consisting of loose sandy or silty soils. The grouting method has had some issues caused by grout materials, and researchers have studied how to address the limitation of the material. The method generally employed in grouting with chemical liquid is the LW (Labile Waterglass) method which is effective for grouting into the gravel and sandy layers, but not effective for grouting into fine sand layers. It is grouted into soft clay soil and silt layers as a vein type effective for preventing sinking and reinforcing grounds. The advantages of the LW method is durability (waterproofing) and improved viscosity of the earth and waterglass-based grouts. The faster speed of current contributes to diluting and losing more chemical liquid to reduce viscosity, and removing more chemical liquid to result in lower durability. Therefore, for the LW method, it is reported that its efficiency is enhanced by raising the chemical liquid concentration, the injection rate and speed with shorter gel time if it is applied to running water ground. Some Korean and overseas researchers have endeavored to study how to replace soft clay ground and loose sandy ground by injecting the cement {biogrouting material (calcium carbonate)} created through bio/chemical reaction of new environment-friendly material microorganisms thereinto to achieve earth cementation, evaluate applicability of the grouting method, and develop environment-friendly materials. This study aims to develop a bio-grouting material in a powder form like cement. Sand gel samples were produced with the ratio of sodium silicate No.3 to water (50 : 50, 35 : 65, 20 : 80), and the ratio of cement to bio-grouting material (100 : 0, 90 : 10, 70 : 30) to select a mixing ratio of bio-grouting, respectively, and then analyzed the Geltime over time. The uniaxial compressive strength was evaluated to select and suggest a mixing ratio optimized for construction conditions. Moreover, on-site test was carried in two locations and an analysis of the result was made to compare applicability and permeability between the conventional LW method, the patented EGMC (Expansibility Grout Admixture Method of Construction) method and the bio-grouting method. The laboratory test reveals that preferred Geltime and uniaxial compressive strength is obtained in 35 : 65 with respect to the ratio of sodium silicate No.3 to water, and 90 : 10 with respect to the ratio of cement to bio-grouting material to demonstrate best standard mixing ratios. The ground improvement effect including permeability and infiltration by the bio-grouting technique was similar to the patented technique in the on-site test construction. However, because of fine particles and a high injection ratio, a significant amount of injection material is required in application to a location with considerable leak and cracks. Therefore, because of fine particles and high mobility of the bio-grouting material, a great effect can be achieved if used as a grouting material applied to rocks. It is thus necessary to develop an application method because more time and efforts are required to procure the bio-grouting material. Furthermore, it is necessary to develop a method for controlling the Geltime by using an additional material (additive) to have more effects.