고밀도 급속 팽창재를 이용한 얕은기초 연약지반의 지지력 증대효과에 관한 연구

Abstract

The soft ground improvement method is one that, using cementation, replacement, and, ramming, seeks safety of ground by increasing bearing capacity of soil, preventing settlement, restraining lateral soil movement, and decreasing soil porosity. Being related this, the soft ground has been explored extensively in the field of geotechnical engineering, and among them, those on grouting addressed various methods and new materials. In the high density polyurethane method, a chemical grouting, the insertion of material causes blowing reaction through chemical reaction, resulting in expansive pressure filling pore in the ground. These filling develop a consolidation that has effect of increases instantaneously increasing shear strength against vertical loads acting on the ground. This suppresses the subsidence and lateral behavior of the ground and generates the waterproofing effect and, as for the structure, is and effective method for increasing the bearing capacity and reducing the amount of settlement of the shallow foundation in constructing middle and low rise structures. The purpose of this study was, accordingly, to reveal the engineering mechanism of the injection material through the laboratory experiment and, based on the field application, to examine the bearing capacity and the stability of the settlement in the shallow foundation. The laboratory experiments performed included the uniaxial compressive strength test, direct shear test, and permeability test, and the field experiment included the plate loading test, earth pressure test, and GPR exploration test. The laboratory experiment results showed that the average internal friction angle was 57°, which was about two times higher than that of the dense sandy soil and the hard clay soil, and that the average adhesive strength was 120 kN/m2, which was 2.5-3.5 times higher than that of the conventional sand and clay samples, which is supposed to be the result of increasing the solid volume of the injected material due to the instantaneous foaming reaction of the expanding material and thus increasing the strength. The field experiments were performed based on the results of laboratory experiments. The results of the plate loading test showed that the allowable bearing capacity for each of the base sections of 3.6×3.6, 4.4×4.4, and 6.0×3.8m increased 1.6-2.6 times after injection of the expansion material. The measured settlements of each base section were 23.1, 22.4, and 19.0 mm, respectively, which were within 50 mm, an allowable settlement, which maybe the result of rising of shallow foundation on soft ground in the process of increasing the volume of the expanding material by nearly 20 times. For the measurement of the displacement of the structure built on the site after ground reinforcement, the inclinometer was attached to the wall on the top of the structure. The measurements were performed three times a year in the first year and twice a year in the second year, for 509 days after completion, showing maximum horizontal displacement of 0.71 mm and the maximum vertical displacement of 0.047 mm, which were very minor ones. Terzaghi and Meyerhof's ultimate bearing capacity theory equations were applied to test the stability. The results showed that, after reinforcement using the expansion material, the bearing capacity was within the allowable bearing capacity and that all the settlements were also within the allowable settlement.