• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.119-130
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• 2008

Uncertainties in physical and engineering parameters for the design of shallow foundations arise from various aspects such as inherent variability and measurement error. This paper aims at investigating and reducing uncertainty from deterministic method by using the reliability-based design of shallow foundations accounting for the variation of various design parameters. A probability distribution type and statistics of random variables such as unit weight, cohesion, infernal friction angle and Young's modulus in geotechnical engineering are suggested to calculate the ultimate bearing capacities and immediate settlements of foundations. Reliability index and probability of failure are estimated based on the distribution types of random variables. Widths of foundation are calculated at target reliability index and probability of failure. It is found that application and analysis of the best-fit distribution type for each random variables are more effective than adoption of the normal distribution type in optimizing the reliability-based design of shallow foundations.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.137-146
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• 2005

299 railroad slopes were investigated and the failure characteristics and reinforcement patterns were analyzed. Stability analyses on the 14 cut-off soil slopes were carried out. Surficial failures were predicted by infinite slope analyses assuming the temporarily perched ground water table at soil surface during rainfall period. Limit equilibrium analyses were also carried out and the influences of rainfall infiltration on the slope stabilities were taken Into account by seepage analyses using finite element method and by assuming ground water tables to be located adjacent to soil surface. The adequacy of those analyses was evaluated by comparing the slope failure characteristics between analysis results and the past failure records. From the comparison results, it was deduced that the limit equilibrium analyses were not appropriate to estimate the shallow failure that occurred at most of the railroad cut-off soil slopes. For the better estimation of the surficial failure, not only the increase of pore-water pressure (reduction of matric suction), but also the influence of water flows over slope surface which erode soil mass, should be evaluated and considered.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.147-160
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• 2008

This paper presents the results of full-scale loading tests performed on 54 passive anchors and 4 group anchored footings grouted to various lengths at several sites in Korea. The test results, the failure mechanisms as well as uplift capacities of rock anchors depend mostly on rock type and quality, embedded fixed length, properties of the discontinuities, and the strength of rebar. Anchors in poor quality rocks generally fail along the grout/rock interfaces when their depths are very shallow (a fixed length of less than 1 m). However, even in such poor rocks, we can induce a more favorable mode of rock pull-up failure by increasing the fixed length of the anchors. On the other hand, anchors in good quality rocks show rock pull-up failures with high uplift resistance even when they are embedded at a shallow depth. Laboratory test results revealed that a form of progressive failure usually occurs starting near the upper surface of the grout, and then progresses downward. The ultimate tendon-grout bond strength was measured from $18{\sim}25%$ of unconfined compressive strength of grout. One of the important findings from these tests is that the measured strains along the corrosion protection sheath were so small that practically the reduction of bond strength by the presence of sheath would be negligible. Based on test results, the main parameters governing the uplift capacity of the rock anchor system were determined. By evaluation of the ultimate uplift capacity of anchor foundations in a wide range of in situ rock masses, rock classification suitable for a transmission tower foundation was developed. Finally, a very simple and economical design procedure is proposed for rock anchor foundations subjected to uplift tensile loads.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.49-59
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• 2013

Heavy rainfall intensity may cause shallow slope failures and debris flow by rill erosion and scour on land surface. The paper represents the difference between native soil (weathered soil) and reinforced soil, which is mixed by hardening agent with flyash as main material, for investigating experimental findings of rill erosion and erosion. Results obtained from artificial rainfall simulator show that erosion rate of reinforced soil mixed with hardening agent is reduced by 20% because an amount of eroded soil on slope surface is inversely proportional to the increase of soil strength. For example, rainfall of 45mm (at the elapsed time of 25mins in rainfall intensity of 110mm/hr) triggers rill erosion on native soil surface, but the rill erosion on reinforced soil surface does not even occur at 330mm rainfall (at the elapsed time of 3hrs in rainfall intensity of 110mm/hr). As a result of slope stability analysis, it was found that the construction method for reinforced soil surface would be more economical, easy and fast construction technology than conventional reinforcement method.

• Proceedings of the Korean Geotechical Society Conference
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• 1994.09a
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• pp.247-252
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• 1994

우리나라 산사태의 대부분은 사면의 깊이가 얕은 상태에서 발생하며, 지형적 지질적 및 강우조건에 따라 각기 다른 사면 파괴의 형태를 보여주고 있다. 본 논문에서는 IFDM의 기법을 이용하여 강우침투에 의해 발생할 수 있는 불포화지반으로의 침윤전선의 진행, 간극수압의 시간적 발생과정 등을 포함하는 침투해석을 수행하였다. 침투해석으로 얻은 강우침투 결과를 hyperbolic 응력, 변형을 모델에 조합하여 시간별로 응력, 변형해석을 할 수 있는 모델을 제안하였다. 이 모델에 의한 해석예로써 용인군 창리 산사태 지역을 선택하여 기존의 한계평형법과 본 논문에서 제안한 모델의 결과를 비교하였다.

• Journal of the Korean Geotechnical Society
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• v.30 no.12
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• pp.5-14
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• 2014

Most of slope failures have taken place between June and September in Korea, which cause a considerable damage to society. Rainfall intensity and duration are very significant triggering factors for landslide. In this paper, landslide-triggering rainfall threshold consisting of rainfall intensity-duration (I-D) was proposed. For this study, total 255 landslides were collected in landslide inventory during 1999 to 2012 from NDMI (National Disaster Management Institute), various reports, newspapers and field survey. And most of the required rainfall data were collected from KMA (Korea Meteorological Administration). The collected landslides were classified into three categories: debris flow, shallow landslide and unconfirmed. A rainfall threshold was proposed based on landslide type using statistical method such as quantile-regression method. Its validation was carried out based on 2013 landslide database. The proposed rainfall threshold was also compared with previous rainfall thresholds. The proposed landslide-triggering rainfall thresholds could be used in landslide early warning system in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1947-1955
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• 2013

The purpose of this paper is to present an photoelasticity technique for measuring the displacement and stress distribution in particle assembly subjected to shallow foundation loading. Photoelastic measurement technique was employed to visualize the force transmission of a particle assembly. A model assembly bounded by a steel frame was built by stacking bi-dimensional circular particles made of polycarbonate elastomer. Each particle was coated by a thin photoelastic sheet so that the force transmission represented by bright light stripes can be visualized. In a contacted particle, both magnitude and orientation of principal stress difference can also be measured via the photoelasticity technique. The different distributions of the contact stresses at the initial loading and near the failure were quantitatively compared. The photoelastic patterns and displacement fields observed in the pre-failure state disappears immediately after the buckling of confined force chains.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.41-49
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• 2003

Rainfall-induced landslides in a weathered granite soil slope usually happen on shallow slip surfaces above the groundwater table. The pore-water pressure of soil above the groundwater table is usually negative. This negative pore-water pressure (or matric suction) has been found to make a large contribution to the slope stability. Therefore, the variation of in-situ matric suction profiles with time elapse in a soil slope should be understood. In this study, a field measurement program was carried out from June to August, 2001 in order to monitor in-situ matric suctions and volumetric water contents in a weathered granite soil slope. Finite-element transient seepage analyses are also conducted using SEEP/W. The influence of climatic conditions on the variation of in-situ matric suctions could be found to decrease rapidly with the change of depth. It could be found that decrement of matric suction induced by precipitation is affected not only by the amount and duration of rainfalls but also by the initial matric suction just prior to rainstorms. The soil-water characteristic from the field monitoring tends toward the wetting path of SWCC obtained from the laboratory test.

• Journal of the Korean Geotechnical Society
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• v.27 no.5
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• pp.45-59
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• 2011

This study introduces the diagrammatic Upper and Lower Bound (UB and LB) methods theoretically in order to derive the bearing capacity factor, $N_c$ in undrained clay and to compare with Prandtl's exact solution (1921). As a result of the theoretical study, an exact solution comes out when the UB and LB solutions are the same. In addition, the finite element analyses show that the failure loads approach to the bearing capacity factor of 5.14. Results of the FEA significantly depend on the finite element type, a number of elements, and a number of increments. From this study the exact solution defines that solutions from UB and LB are the same. However, this situation is very difficult to process, so we can confirm the exact solution as a range between UB and LB solutions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.3
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• pp.237-246
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• 2021

With climate change, debris flow has been increasing due to the collapse and erosion of shallow slopes caused by extreme rainfall. It is preferred to an economical and eco-friendly method rather than reinforcement of soil slopes with the earth anchor or nailing method. In this study, a soil improvement agent was developed by utilizing insitu soil, leaf mold, and used harbal medicine to help sufficient vegetation. In addition, to prevent surface erosion, shear strength of the soil was increased by using micro cement and hemihydrate gypsum as additives. The optimum mix ratio of the mixture is determined by increasing the shear strength by checking the erosion progress of the ground surface layer due to rainfall through an laboratory test. The safety factor of soil slope has been improved on the slope surface reinforced by the improvement agent, and the strength of erosion has been increased, making it efficient to cope with heavy rain during wet season.