• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.33 no.4
• /
• pp.168-178
• /
• 2021

Numerical simulations were implemented to look into the modified seabed topography due to the presence of breakwaters of varying reflection characteristics. The numerical model was composed of OlaFlow, an OpenFoam-based tool box, and a physics-based morphology model [Seoul Foam]. In doing so, the interaction between the seabed, which undergoes deformation due to siltation and scouring, and the incoming waves was described using Dynamic Mesh. The rubble-mound, vertical, and curved slit caisson breakwaters with varying reflection characteristics resulted in standing waves that differ from each other, shown to have a significant influence on the seabed topography. These results are in line with Nielsen's study (1993) that sands saltated under the surface nodes of standing waves, where the near-bed velocities are most substantial, convected toward the surface antinodes by boundary-layer drift. Moreover, the crest of sand waves was formed under the surface antinodes of standing waves, and the trough of sand waves was formed under the surface antinodes. In addition, sand wave amplitude reaches its peak in the curved slit caisson with a significant reflection coefficient, and the saltation of many grains of sand would cause this phenomenon due to the increased near-bed velocity under the nodes when the reflection coefficient is getting large.

• Clean Technology
• /
• v.15 no.1
• /
• pp.54-59
• /
• 2009

In this study, the separation of water/bitumen emulsion was investigated by chemical demulsification method. Motor oils (GS Caltex Deluxe Gold V 7.5W/30, Hyundai gear oil 85W/140) and asphalt (AP-5, KS M 2201, Dongnam Petrochemical MFG. Co.) were used as model oils in the preliminary experiments to effectively remove water from water/bitumen emulsion. The bitumen extracted from Canadian oilsands was used in this study. The water/oil emulsion was not separated without demulsifiers, and Hyundai motor oil showed higher efficiency of water separation at a low concentration of demulsifier compared with that for GS Caltex motor oil. However, as the concentration increased, the efficiency did not rapidly increase compared with that of GS Caltex motor oil. It was highly speculated that the water phase of Hyundai motor oil was not dispersed well compared with that of GS Caltex motor oil because the viscosity of Hyundai motor oil was much higher than that of GS Caltex motor oil. The demulsifier of higher HLB (hydrophilic - lipophilic balance) value had high separation efficiencies in water/oil emulsion. The TWEEN 20 (polyoxyethylene sorbitan monolaurate solution) showed better separation efficiency than other demulsifiers.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.4
• /
• pp.5-13
• /
• 2007

Many construction projects adopt grouting technology to prevent the leakage of groundwater or to improve the shear strength of the ground. Recognition as a feasible field procedure dates back to 1925. Since then, developments and field use have increased rapidly. According to improvement of grout materials, theoretical study on grout penetration characteristics is demanded. Fluid of grout always tends to flow from higher hydraulic potential to lower one and the motion of grout is also a function of formation permeability. Viscosity of pout is changed by chemical action while grout moves through pores. Due to the increment of viscosity, permeability is decreased. Permeability is also reduced by grout particle deposits to the soil aggregates. In this paper, characteristics of new cement grout material that has been developed recently are studied: injectable volume of new grout material is tested in two different grain sizes of sands; and the method to calculate injectable volume of grout Is suggested with consideration of change in viscosity and clogging phenomena. The calculated values are compared with injection test results. Viscosity of new grout material is found to increase as an exponential function of time. And lumped parameter $\delta$ of new grout material to be used for assessing deposition characteristics is estimated by comparing deposit theory with injection test results considering different soil types and different injection pressures. Injection test results show that grout penetration rate is decreased by the increase of grout viscosity and clogging phenomena.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.4
• /
• pp.161-167
• /
• 2007

In this study, ultimate lateral load capacity of piles is analyzed with consideration of lateral stress effect. Based on results obtained in this study, a method for the estimation of ultimate lateral load capacity is proposed. This makes it possible to more realistically estimate the ultimate lateral load capacity under various stress states caused by in-situ soil condition and pile installation process. Calibration chamber test results with various soil conditions were used in the analysis. From the test results, it was found that effect of the lateral stress was greater than that of the vertical stress on the ultimate lateral load capacity of piles. It was also found that, as the relative density increases, displacements required to reach the ultimate state increases, showing relative displacements of around 14% and 18-25% for $D_R$ : 55% and 86%, respectively. Based on results obtained in this study, a methodology for the estimation of ultimate lateral load capacity of piles using correction factors was proposed. Results from proposed method matched well measured results.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.8
• /
• pp.35-45
• /
• 2007

It is known that the response of piles is affected by the shape of pile as well as soil conditions. In order to investigate the characteristics of the axial responses and bearing capacities of non-displacement tapered and cylindrical piles in sands, 12 model pile load tests using a calibration chamber were conducted on model tapered and cylindrical piles, which were specially manufactured to measure the base and shaft load capacities independently. Results of the model tests showed that the shaft load of tapered piles continuously increased with pile settlement, whereas the shaft load of cylindrical piles reached ultimate values at a settlement equal to 4% of pile diameter. Therefore, taper piles have greater shaft loads than cylindrical one at the same settlement. It is also observed that the total load capacity of tapered piles is lower than cylindrical piles for dense sand but is greater than that of cylindrical piles for medium sand. The ultimate unit base resistance of tapered piles was greater than that of cylindrical piles for lateral earth pressure ratio greater than 0.4, and the shaft resistance was greater than that of cylindrical piles irrespective of lateral earth pressure ratio.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.1
• /
• pp.91-99
• /
• 2008

The method to prepare the large cemented sand specimen for calibration chamber test by air-pluviation is investigated in this study. The uniformity of cemented specimen is evaluated by performing the CPTs, DMTs, and bender element tests in the calibration chamber. The sand particles, pre-wetted with 0.5% water content, are mixed with gypsum to provide the homogeneous coating of gypsum particles on the grain surface. It was shown that the pre-wetting of particle surface is effective to minimize the potential for segregation between sands and gypsum during air-pluviation. It was observed that the extreme void ratios ($e_{max}\;and\;e_{mix}$) of the mixture of pre-wetted sand and gypsum powder increase at lower gypsum content while those of the mixture of dry sand and gypsum decrease with increasing gypsum content. It was also shown from the test results that large cemented specimens reconstituted in calibration chamber by rainer system are quite uniform in vertical and horizontal directions.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.11
• /
• pp.105-115
• /
• 2009

The Jeju sand was sampled from the beach in Jeju Island and its basic properties were analyzed. The cementation effect of Jeju coastal sediments was evaluated from in-situ tests such as SPT, CPT, and the Suspension-PS test. It was shown from test results that the Jeju sand has high extreme void ratios due to the angularity of grains and the intra-particle voids of hollow particles, similar to typical calcareous sands. From cone penetration test in the calibration chamber, it was found that the cone resistance($q_c$)-relative density($D_R$)-vertical effective stress(${\sigma}_v'$) relation of Jeju sand almost matches that of high compressible quartz sand. However, the $q_C-D_R-{\sigma}_v'$ correlation suggested for uncemented Jeju sand overestimates the relative density of coastal sediments of Jeju Island due to the cementation effect. From the analysis of the relation of cone resistance, N value, and small strain shear modulus measured in-situ, it seems reasonable to assume that the coastal sediment of Jeju Island is a naturally cemented one.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.10
• /
• pp.61-68
• /
• 2010

A pilot-scale model test was performed to estimate the availability of new material, Fe-loaded zeolite, as the filling material in permeable reactive barrier (PRB) against the contaminated groundwater with both Cd and Cr(VI). Aquifer was simulated by filling up a large scale soil tank with sands, and mobilizing the water flow by the head difference of water level in both ends of the tank. Then, the mixture of concentrated Cd and Cr(VI) solution was injected into the aquifer to form a contaminant plume, and its behavior through Fe-loaded zeolite barrier was monitored. The test results showed that Fe-loaded zeolite barrier successfully treated the contaminant plume containing both Cd and Cr(VI) and that the immobilized contaminants in the barrier were not desorbed or released. The results indicated that the Fe-loaded zeolite could be a promising material in PRBs against the multiple contaminants with different ionic forms like Cr(VI) and Cd.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.5
• /
• pp.77-88
• /
• 2007

Lateral earth pressure and horizontal displacement of the diaphragm walls constructed in multi-soil layers were analyzed by the field instrumentation from six building construction sites in urban area. The distribution of the developed earth pressure of the anchored diaphragm walls during excavation shows approximately a trapezoid diagram. The maximum earth pressure of anchored diaphragm walls corresponds to $0.45{\gamma}H$ and the earth pressure acts at the upper part of the walls. The maximum earth pressure is two times larger than the empirical earth pressure of flexible walls in sands suggested by Terzaghi and Peck(1967), Tschebotarioff(1973), and Hong and Yun(1995a). The horizontal displacement of diaphragm walls is closely related with supporting systems such as struts, anchors, and so on. The horizontal displacement of anchored walls shows less than 0.1 percent of the excavated depth, and the horizontal displacement of strutted walls shows less than 0.25 percent of the excavated depth. Therefore, the restraining effect of horizontal displacement to the anchored diaphragm walls is larger than the strutted diaphragm walls. In addition, since the horizontal displacement of the diaphragm walls is lower than the criterion, $\delta=0.25%H$, used for control the anchored retention wall using soilder piles, the safety of excavation sites applied with the diaphragm walls is pretty excellent.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.1C
• /
• pp.53-62
• /
• 2008

A constitutive model, which can simulate the effect of principal stress rotation associated with direct simple shear test, is proposed in this study. The model is based on two mobilized planes. The plastic strains occur from the two mobilized planes, and depend on stress state, and they are added. The first plane is a plane of maximum shear stress, which rotates about the horizontal axis, and the second plane is a horizontal plane which is spatially fixed. The second plane is used to consider the effect of principal stress rotation on simple shear tests under different stress states. The soil skeleton behavior observed in drained simple shear tests is captured in the model. This constitutive model is incorporated into the dynamic coupled stress-flow finite difference program FLAC. The model is first calibrated with drained simple shear tests on loose Fraser River sand. The measured shear stress and volume change are partially induced by principal stress rotation and compared with model calculations. The model is verified by comparing predicted and measured settlements due to rigid footing resting on loose sands. Settlements predicted by the proposed model were very similar to measured settlements. Mohr-Coulomb model can not consider the effect of principal stress rotation and its prediction was only 20% of measured settlements.