실트질 사질토에서 지진 시 배수조건에 따른 지반거동 분석

Abstract

In this study, laboratory tests were conducted to analyze the physical and mechanical properties of silt, silty sand and sand soils in Saemangeum and Incheon areas, where are expected to build large-scale facilities by dredging and reclamation in Korea. The soil physical properties of Saemangeum area were analyzed as water content 25.8~30.8%, specific gravity 2.60~2.68, initial void ratio 0.682~0.825, uniformity coefficient 6.6~22.3, coefficient of curvature 1.4~4.5, and 12~72% of fine contents ratio. Physical properties of Incheon soil show water content 8.0~10.6%, specific gravity 2.62, initial void ratio 0.209~0.278, uniformity coefficient 7.3~12.2, coefficient of curvature 0.7~0.9, and 7.6~8.1% of fine contents ratio. In order to determine the liquefaction cyclic resistance ratio of soils sampled from Saemangeum and Incheon areas, cyclic triaxial tests were conducted. In the case of silt, the cyclic resistance ratio(CRR) was 0.176~0.205, CRR=0.179~0.225 for silt sand, and 0.203~0.216 for sand. According to test results, in the case of silt samples with a large amount of fines including clay, it was found that the number of loading cycles required to reach liquefaction at the same relative density was less than the sample that did not. In other words, in the case of a sample with a large content of fines, it reaches the liquefied state in a short time. However, the silty sand samples with a some amount of fines including small amount clay delayed the time to reach the liquefied state. The reason for the increase in the liquefaction Cyclic Resistance Ratio(CRR) is that the amount of clay particles is small, which results less effect the decrease of permeability and frictional resistance between particle. A similar trend was also observed for sand, which does not contain clay. In the case of Saemangeum area composed of silt and silt sand with a large content of fines, it was analyzed as undrained drainage condition during earthquake. In the case of Incheon area composed of large amount of sand was analyzed by FEM as a drained drainage condition to figure out the behavior after the earthquake. For Saemangeum area, the excess pore water pressure ratio(EPWPR) during earthquake was 0.7. For Incheon are, the excess pore water pressure ratio was found to be 0.3. It was confirmed that both areas were not reached liquefaction state, but only partial liquefaction were reached. In Saemangeum area, the drainage condition of the ground was analyzed as undrained. In this case, the horizontal displacement occurred largely at the point where the surcharges load was small, and in the order of the front part of the structure, the structure, and the landfill site. The maximum displacement was observed in the short-period earthquake and the smallest displacement in the domestic earthquakes. It was found that the front of the structure was swelled due to the settlement of the substructure under the structure. It was interpreted that the maximum settlement occurs in the short-period earthquake and the minimum it in the domestic seismic. In the Incheon area analyzed by drainage conditions, it was found that the excess pore water pressure generated during the earthquake gradually dissipated after the earthquake, resulting in additional horizontal and vertical (settlement) displacements. In the normal and reverse fault earthquake, short-period and artificial seismic, the maximum settlement occurred during an earthquake, and the domestic seismic earthquake showed that the minimum settlement occurred during an earthquake. After the earthquake, it was found that additional displacement due to the dissipation of excess pore water pressure occurred in all seismic waves. At all points, long-period seismic dissipate late in the excess pore water pressure after the earthquake. It was found that about 50% of the total settlement at some points of the long-period earthquake occurred as a result of the dissipation of excess pore water pressure after the earthquake. Therefore, it is necessary to continuously study the ground behavior that occurs as the excess pore water pressure is dissipated after the earthquake.