친환경 바이오그라우팅공법에 대한 모래지반에서의 적용성 평가

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. International and domestic research on implementation of biogrout using bio byproduct materials on soft clayey and loose sandy soils was performed. The common purposes of these past studies were (1) to achieve cementation of soft soils, (2) to evaluate field applicability of developed methods, and (3) to develop environment-friendly materials improving soil strength and reducing compressibility. Despite the past research results, more efficient biogrouting method is required; therefore, new biogrouting methods were developed in this study. The objectives of this study can be summarized as follows:

1) Production of optimal powdery biogrout material for the implementation of Microbial Calcite Precipitation (MCP) method: To achieve the goal, mixtures of different specimens were made varying mixture ratios of non-treated, biogrout-treated, cement-treated, biogrout and cement treated (biogrout to cement ratios of 1:9, 3:7, 5:5) soils and fines of 0%, 5% and 15%. From the comparison of uniaxial compression test results (uniaxial compression strengths at curing days of 7 and 28 days) of these non-treated and treated mixtures, mixtures’ strength improvement was quantitatively evaluated to analyze the effects of the soil treatment and to evaluate the treatments’ economic efficiency. 2) Development of biogrouting injection methods for different ground conditions [from well-graded sand, fine to coarse (SW) sands to poorly graded (SP) sand under different relative compactions (RC) of 70%, 80%, 85%, 90%, 95%]: The effects of injection rate on diffusion range of cementation and cementation strength were evaluated. In addition, practicality and applicability of biogrouting were assessed. 3) Evaluation of strengthening effects of the Labiles Waterglass (LW) grout and the biogrout by mixing different grouting materials [Ordinary Portland Cement (OPC), Micro cement, Biogrout and Sodium silicate No. 3]. 4) Deduction of an optimal biogrout method, by evaluating cementation created from the reaction of environment-friendly material microorganisms. Strength and waterproofing effects after the biogrout and in-situ applicability were estimated based on the Bender element test results. Chemicals and cements were not used in grouting. 5) Validation of environmental safety of the biogrout materials based on the results of the fish toxicity tests: The environment effects of the LW method and the biogrout method were compared. This aims to analyze the positive effect of biogrout on the environment from the examination of soil contamination.

Uniaxial compressive strengths of sand-gel (biogrout material to Cement mixing ratio of 3:7) specimens were as high as approximately 85% of the cement treated specimens’ strengths. From the strength comparison on the homo-gel specimens, the strengths of the injection materials OB-1 (OPC 100% + biogrout 30%) and MB-1 (micro 100% + biogrout 30%) were 15% higher than those of the OPC and micro injection materials.

It is the mixing ratio for reducing the amount of cement used. About the homo-gel specimens, comparison results of the strength of the injection materials OB-1 (OPC 100% + Biogrout 30%) and MB-1 (Micro 100% + Biogrout 30%) showed the strengths about 15% higher than those of the OPC and micro injection material. In the injection materials OS (OPC 100% + Sodium silicate 30%) and MS (Micro 100% + Sodium silicate 30%) containing sodium silicate No. 3, strength was reduced by 50%∼70%. This indicates that biogrout can be a good potential candidate as a supplementary cementation material replacing the LW injection materials. Results of the laboratory biogrouting test, 100% injection efficiency was achieved on the SP specimens under RC of 70% ~ 85%; however, reduction of injection efficiency was identified when RC exceeded 90%. For the SW specimens, the injection ratio was less than 10% when RC exceeded 85%. Therefore, it is concluded that the applicability of biogrout are highly dependent on ground conditions. The moduli of the materials increased with increasing curing time. Comparison results of the shear modulus for the LW injection materials and the biogrout injection materials revealed that the shear moduli of the OB-1 and MB-1 injection materials were approximately 15% higher than those of the OPC and Micro cement materials. The fish toxicity test results showed that the biogrout material is more environment-friendly material compared to the LW injection materials. In this study, an environment-friendly biogrout is newly developed and is compared with the existing LW method based on the results of injection experiments conducted under conditions similar to the actual sites. From the research, it is concluded that the developed biogrouting method can be an efficient method and has high potentials of field implementation.