• Journal of the Korean GEO-environmental Society
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• v.24 no.1
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• pp.5-14
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• 2023

In this study, the load transfer characteristics of the base and skin of drilled shafts were analyzed and the load sharing ratio was calculated by performing a load transfer large-scale model test and three-dimensional numerical analysis considering the similarity of drilled shafts, which is the design target. From the linear behavior of drilled shafts shown in the large-scale model test and 3D numerical analysis results, the skin load transition curve for the design conditions of this study was proposed by Baquelin et al., and the base load transition curve was proposed by Baquelin et al. For the horizontal load transition curve, the formula proposed by Reese et al. was confirmed to be appropriate. The test value was slightly larger than the numerical analysis value for the axial load at the rock socketing, but the load sharing ratio at the rock socketing increased, on average, about 27.8% as the vertical load increased. The analysis value of the vertical settlement of the pile head under the vertical load was evaluated to be slightly smaller than the test value, and the maximum vertical settlement of the pile head in the model test and analysis maximum vertical load was 10.6 mm in the test value and 10.0 mm in the analysis value, and the maximum vertical settlement value at the base of the pile was found to be a test value of 2.0 mm and an analysis value of 1.9 mm. The horizontal displacement at the head of the column (ground surface) and the head of the pile during the horizontal load was found to agree relatively well with the test value and the analysis value. As a result of the model soil test, the horizontal load measured at the maximum horizontal displacement of 38.0 mm was evaluated to be 24,713 kN, and the horizontal load in the numerical analysis was evaluated to be 26,073 kN.

• Journal of the Korean Geotechnical Society
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• v.26 no.8
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• pp.27-37
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• 2010

Downdrag force develops when a pile is driven through a soil layer which will settle more than a pile. There is no obvious criterion for application of the current pile design method considering the negative skin friction. Therefore, in this study, numerical analyses were performed to investigate the behavior of a single pile subjected to negative skin friction and their results were used to determine the applicability of the current design method. Including three different sites in Song-do area and two different cases with friction pile and end bearing pile conditions, total six cases were considered. The load-settlement relationships and the neutral points were estimated for different end bearing conditions and the allowable bearing capacity of piles with negative skin friction was investigated through parametric studies. Based on the results showed that the negative skin friction made a major influence on the settlement of a pile and its stress. However the allowable bearing capacity may not be influenced by the negative skin friction. Compared with the allowable bearing capacity obtained from the ultimate bearing capacity with the safety factor of 3, the current design method with the safety factor of 3 underestimated the allowable bearing capacities regardless of the end bearing conditions. On the other hand, the current design method with the safety factor of 2 yielded reasonable results depending on the end bearing conditions.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.65-76
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• 2007

Recently, there have been many construction projects on soft ground with growth of industry and various construction problems concerning soft soil behavior also have been reported. Especially, foundation piles of abutments and (or) buildings which were constructed on the soft ground have been suffering from a lot of stability problems of inordinary displacement due to lateral flow of soft ground. Although many researches for this phenomena have been carried out, it is still difficult to assess the mechanism of lateral flow on soft ground quantitatively. And reliable design method for judgement of lateral flow occurrence is not established yet. In this study, PNN (probabilistic neural network) and CNN (committee neural network) theories were applied for judgment of lateral flow occurrence based on eat data compiled from Korea and Japan. Predictions of PNN and CNN models for new data which were not used during model development are compared with those predicted by conventional empirical methods. It was found that the developed PNN and CNN models can predict more precise and reliable judgment of lateral flow occurrence than conventional empirical methods.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.77-88
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• 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
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• v.28 no.1C
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• pp.53-62
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• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1C
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• pp.63-72
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• 2006

Due to rapid development of many cities in Korea, many public facilities are required to be built as well as complementary civil structures. Consequently, a number of tunnel constructions are currently carried out throughout the country, and many more tunnels are planned to be constructed in the near future. Tunnel excavation in a city often causes serious damage to above-ground structures and sewer system because of unexpected settlement. In order to prevent the destruction, the tunnel, which bypasses the center of a city, must be specially evaluated for its influence to other structure. In addition, since a slight disturbance of above-ground structure causes numerous public complaints and civil appeals, it must be approached with different method than the mountain tunnels. In this paper, the evaluation method using the Artificial Neural Network (ANN) has been studied. The method begins with an analysis of the minimal sectional area. If its result can be used to approximate the general influence of the whole section, the actual evaluation using ANN will take off. In addition, it also studies the construction management method which reflects the real time soil behavior and environment influence during construction using Geographic Information System (GIS).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.85-93
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• 2010

The shear stiffness has become an important design parameter to understand the soil behavior. In particular, the elastic moduli and void ratio has been considered as important parameters for the design of the geotechnical structures. The objective of this paper is the development of the penetration type Field Velocity and Resistivity Probe (FVRP) which is able to assess the elastic moduli and void ratio based on the elastic wave velocities and electrical resistivity. The elastic waves including the compressional and shear wave are measured by piezo disk elements and bender elements. And the electrical resistivity is measured by the resistivity probe, which is manufactured and installed at the tip of the FVRP. The penetration tests are carried out in calibration chamber and field. In the laboratory calibration chamber test, after the sand-clay slurry mixtures are prepared and consolidated. The FVRP is progressively penetrated and the data are measured at each 1 cm. The field experiment is also carried out in the southern part of Korea Peninsular. Data gathering is performed in the depth of 6~20 m at each 10 cm. The elastic moduli and void ratio are estimated based on the analytical and empirical solutions by using the elastic wave velocities and electrical resistivity measured in the chamber and field. The void ratios based on the elastic wave velocities and the electrical resistivity are similar to the volume based void ratio. This study suggests that the FVRP, which evaluates the elastic wave velocities and the electrical resistivity, may be a useful instrument for assessing the elastic moduli and void ratio in soft soils.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.47-60
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• 2023

At present, in South Korea, there is a growing concern regarding solar power facilities installed on slopes because they are prone to damage caused by natural disasters, such as heavy rainfall and typhoons. Each year, these solar power facilities experience soil erosion due to heavy rainfall and foundation damage or detachment caused by strong wind loads. Despite these challenges, the interaction between the ground and structures is not adequately considered. Current analyses primarily focus on the structural stability under external loads; the overall facility site's stability-excluding the solar structures-in relation to its surrounding slopes is neglected. Therefore, in this study, we use finite-difference method analysis to simulate the behavior of the foundation and piles to assess changes in lateral displacement and bending stress in piles, as well as the safety factor of sloped terrains, in response to various influencing factors, such as pile diameter, spacing between piles, pile-embedding depth, wind loads, and dry and wet conditions. The analysis results indicate that pile spacing and wind loads significantly influence lateral displacement and bending stress in piles, whereas pile-embedding depth strongly influences the safety factor of sloped terrains. Moreover, we found that under certain conditions, the design criteria in domestic standards may not be met.

• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.9-17
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• 2024

When constructing on soft ground, managing ground settlement and safety is crucial. However, there often exists a significant disparity between the actual behavior of the ground and the design plans. In this study, we aimed to compare and analyze the difference between the predicted settlement based on theoretical formulas and the measured settlement during construction, in order to predict settlement. For this purpose, we analyzed settlement data from 18 construction sites. The results indicated that the back analysis settlement values were similar to the measured settlement values, whereas the design settlement values were significantly higher compared to the measured settlement values. Specifically, the design settlement values were 1.2 to 1.4 times higher than those derived from back analysis using measured values. The RMSE analysis revealed a value of 0.6212m for the design settlement and 0.1697m for the back analysis settlement. The difference between the back analysis settlement and the measured settlement was more than 70% lower than the difference between the design settlement and the measured settlement. This indicates that the back analysis settlement values exhibit lower error rates compared to the design settlement values.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.87-102
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• 1991

It has been reported that the failure of Carsington Dam in Eng1and occured due to the existence of a thin yellow clay layer which was not identified during the design work, and due to pre-existing shears of the clay layer. The slope stability analyses during the design work, which utilized traditional circular arc type failure method and neglected the existence of the clay layer, showed a safety factor of 1.4. However, the post-failure analyses which utilized translational failure mode considering the clay layer and the pre-existing shear deformation revealed the reduction of safety factor to unity. The post-failure analysis assumed 10。 inclination of the horizontal forces onto each slice based on the results of finite element analyses. In this paper, Bishop's simplified method, Janbu method, and Morgenstern-Price method were used for the comparison of both circular and translational failure analysis methods. The effects of the pre-existing shears and subsquent movement were also considered by varying the soil strength parameters and the pore pressure ratio according to the given soi1 parameters. The results showed factor of safefy 1.387 by Bishop's simplified method(STABL) which assumed circular arc failure surface and disregarding yellow clay layer and pre-failure material properties. Also the results showed factor of safety 1.093 by Janbu method(STABL) and 0.969 by Morgenstern-Price method(MALE) which assumed wedge failure surface and considerd yellow clay layer using post failure material properties. In addition, dam behavior was simulated by Cam-Clay model FEM program. The effects of pore pressure changes with loading and consolidation, and strength reduction near or at failure were also considered based on properly assumed stress-strain relationship and pore pressure characteristics. The results showed that the failure was initiated at the yellow clay layer and propagated through other zones by showing that stress and displacement were concentrated at the yel1ow clay layer.