• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.311-317
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• 2003

The swelling index of clayey soil was examined by constant rate of strain(CRS) consolidation test. Four kinds of strain rate were applied during unloading. The strain rates are l/l, l/5, 1/10, l/l 5 of loading. The strain rates during loading are 0.05%/min and 0.03%/min. From the test results using standard consolidometer, the swelling indexes were much similar values in case of 1/5 or 1/10 of the strain rate during loading stage. In the relation between effective stress and excess pore water pressure ratio, it was found that the existence of cross point and the stress level can be separated into two zones according to the swelling index.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.529-536
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• 2005

Based on an estimating method for post-cyclic strength and stiffness with cyclic triaxial tests, Direct Simple Shear (DSS) tests were carried out to confirm whether the method can be adapted to DSS test on fine-grained soils: silty clay, plastic silt, and non-plastic silt. Results from post-cyclic DSS tests were interpreted by a modified method as adopted for post-cyclic triaxial tests. In particular, influence of plasticity index for fine-grained soils was emphasised. Findings obtained from the present study are: (i) the higher the plasticity index of fine-grained soils is, the less not stiffness ratio but strength ratio decreases with increment of a normalised excess pore water pressure; and (ii) post-cyclic strength and stiffness results from DSS tests agree well with those predicted by the method modified from a procedure used for triaxial test results.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.320-327
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• 2005

Liquefaction characteristics of saturated sand under various dynamic loadings such as sinusoidal, wedge, increasing wedge and real earthquake loading are investigated focusing on the excess pore water pressure build up instead of liquefaction resistance strength in this paper. There are large differences between two types of earthquake loading - impact and vibration in liquefaction characteristics. The angle of phase change line of sinusoidal loading is very close to the vibration type, whereas the cumulative deviator stress and cumulative plastic strain are larger than two types of real earthquake loadings. On the other hand, the liquefaction characteristics of increasing wedge loadings are located in the range between vibration and impact earthquake loadings. It is concluded that the sinusoidal loading overestimates the resistance of soil under real earthquake loading. Based on results obtained, the increasing wedge loading can reflect the liquefaction behavior under real earthquake loadings more efficiently than sinusoidal loading based on equivalent uniform stress concept.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1086-1093
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• 2005

In soft ground, consolidation settlement is mainly consider. The primary consolidation settlement which is the time when the excess pore water pressure is completely dispersed and the secondary consolidation settlement which follows. Recently as the depth of consolidation layer increases the consideration of not only the primary consolidation settlement but also of the secondary consolidation settlement becomes a very important element. But up to the present there were only a few in-depth study of the secondary consolidation settlement performed. At present there are a lot of methods available when it comes to the improvement of soft soil. In this study, Preloading Method which is the most commonly used soft soil improvement method locally was used in order to investigate the method for the reduction of secondary consolidation settlement. The objective of this study is to determine the amount of preloading required to reduce secondary consolidation settlement and to determine whether secondary consolidation settlement using standard consolidation test.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.665-681
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• 2023

Liquefaction is one of the most devastating geotechnical phenomena that severely damage vital structures and lifelines. Before constructing structures on problematic ground, it is necessary to improve the site and solve the geotechnical problem. Among ground improvement methods dealing with liquefaction, gravel drain (GD) columns and deep soil mixing (DSM) columns are popular. In this study, the results of a series of seismic experiments in a 1g environment on a structure located over liquefiable ground with different thicknesses reinforced with GD and DSM techniques were presented. The dynamic response of the reinforced ground system was investigated based on the parameters of subsidence rate, excess pore water pressure ratio, and maximum acceleration. The time history of the input acceleration was applied harmonically with an acceleration range of 0.2g and at frequencies of 1, 2, and 3 Hz. The results show that the thickness of the liquefiable layer and the frequency of the input motion have a significant impact on the effectiveness of the improvement method and all responses. Among the two techniques used, DSM in thick liquefied layers was much more efficient than GD in controlling the subsidence and rupture of the soil under the foundation. Maximum settlement values, settlement rate, and foundation rotation in the thicker liquefied layer at the 1-Hz input frequency were higher than at other frequencies. At low thicknesses, the dynamic behavior of the GD was closer to that of the DSM.

• Geomechanics and Engineering
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• v.33 no.3
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• pp.231-242
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• 2023

This paper represents a comparative study in which Gene Expression Programming (GEP), Group Method of Data Handling (GMDH), and multiple linear regressions (MLR) were utilized to derive new equations for the prediction of time-dependent bearing capacity of pile foundations driven in cohesive soil, technically called pile set-up. This term means that many piles which are installed in cohesive soil experience a noticeable increase in bearing capacity after a specific time. Results of researches indicate that side resistance encounters more increase than toe resistance. The main reason leading to pile setup in saturated soil has been found to be the dissipation of excess pore water pressure generated in the process of pile installation, while in unsaturated conditions aging is the major justification. In this study, a comprehensive dataset containing information about 169 test piles was obtained from literature reviews used to develop the models. to prepare the data for further developments using intelligent algorithms, Data mining techniques were performed as a fundamental stage of the study. To verify the models, the data were randomly divided into training and testing datasets. The most striking difference between this study and the previous researches is that the dataset used in this study includes different piles driven in soil with varied geotechnical characterization; therefore, the proposed equations are more generalizable. According to the evaluation criteria, GEP was found to be the most effective method to predict set-up among the other approaches developed earlier for the pertinent research.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.1
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• pp.67-75
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• 2024

In the case of the Pohang earthquake, which had a magnitude of 5.4 in 2017, geotechnical damages such as liquefaction and ground settlement occurred. The need for countermeasures has emerged, and experimental research in the Pohang area has continued. This study collected undisturbed samples from damaged fine-grained soil areas where ground settlement occurred in Pohang. Cyclic tri-axial tests for identifying the dynamic characteristics of soils were performed on the undisturbed samples, and the results were analyzed to determine the cause of ground settlement. As a result of the study, it was determined that in the case of fine-grained soils, ground settlement occurred because the seismic load as an external force was relatively more significant than the shear resistance of the very soft fine-grained soils, rather than due to an increase in excess pore water pressure.

• Geotechnical Engineering
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• v.12 no.6
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• pp.65-78
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• 1996

The Chungpyung Dam is a 16 yearn old rock-fill dam for a Pumped storage hydro-Power plant, located in the middle of the Korean Peninsula. Since the dam is subjected to the daily water level fluctuation, such as rapid drawdown and refill, thus inducing a structural impact on the behavior of dam body, it draws attention of many engineering concerns. Traditionally, steady-state analysis was employed to investigate the seepage in the dam body, but in this study the seepage analysis was numerically performed by 2-D FEM thansient analysis. As a boundary condition for an analysis, the water level fluctuation was incorporated to simulate the daily change. As a res41t, the various seepage phenomena such as hydraulic gradient, seepage vector, and pore water pressure distribution were quantified at the corresponding time of interest as the water level rises and recedes. The seepage flux was also estimated and compared with the measured data which were both acceptable considering design criteria. The result proves that there is no sign of hazardous sources contributing to the possibility of piping, internal erosion and excess leakage through the dam body.

• Geotechnical Engineering
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• v.3 no.1
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• pp.7-24
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• 1987

Preloading surcharge method along with vertical drains was adopted to improve the performance of a very soft marine clay deposit. The onshore deposit, located in the Ulsan Bay area, consists of a 2 to 10m thick, very soft, highly compressible marine clay layer developed just below. the sea water level. The initial undrained shear strength of the clay layer was about 0.6 ton/m2. But, the deposit was designed after treatment to support some auxiliary facilities for a new ilo refinery plant, requiring bearing capacities of 3.6 to 5.4 ton/m2 and maximum allowablee settlement of less than 7.5cm. A total of 35, 000 wick drains Ivas installed to expedite drainage during preloading, and surcharge loads of up to 5m above the original ground level were applied in a step-by-step loading sequence to prevent ground failure by excess surcharge loads. An extensive program of field instrumentation was implemented to monitor the behavior of the clay deposit. Measurers!ends included settlements, excess pore pressure and its dissipation, ground farmer level fluctuation, and lateral movement of the so(t clay layer under the preloads. This paper describes the design concepts, construction methods and control procedures used for improvement of the clay layer. It also presents the ground behavior measured during construction, rind comparisons with theoretical predictions.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.25-38
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• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.