• Journal of the Korean Geosynthetics Society
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• v.4 no.2
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• pp.47-56
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• 2005

Recently, geosynthetic reinforced earth walls are gradually replacing conventional concrete retaining walls for reasons of economy, expediency of construction, and aesthetics. A number of reinforced soil walls having more than 10m heights have been constructed to make more effective development in the country. However, mistakes in design and construction of reinforced earth walls have resulted in many troubles such as failure of reinforced earth walls, horizontal deformationor breakdown of facings, and so forth during or after construction. In this paper, a case study on global sliding failure of a geogrid-reinforced tiered wall is carried out to investigate the causes of the failure and suggest the proper countermeasures. From the subsurface investigation and field instrumentation, It is found that the cause of the global sliding failure was occurred by decreasing of bearing capacity of foundation ground induced by infiltration of rainwater.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.81-91
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• 2005

This paper is the results of experimental and numerical works on the investigating design factors influencing the bearing capacity, the ratio of stress concentration, and the failure mechanism of the clay ground improved with sand compaction piles (SCP). In order to find the behavior of the clay ground improved with SCP, extensive centrifuge model experiments were carried out for each of the SCP replacement ratio of 20, 40, and $70\%$, the non-plastic fine contents in sand of 5, 10, and $15\%$, and the ratio of the improved width to the loaded area (W/B) of 1, 2, and 3. The commertially available software of FEM, CRISP, was used to analyze test results by performing numerical estimations. In these numerical analyses the sand compaction piles and the clay ground were simulated as a linear elastic and plastic constitutive model and the modified Cam-clay model, based on Critical State Soil Mechanics, respectively.

• Geotechnical Engineering
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• v.6 no.4
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• pp.7-18
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• 1990

To deal with the case of a rigid retaining wall built close to a stable rock face with cohesionless backfill, analytical solution methods Proposed by Spangler- Handy and Sokolovskii are modified. The modified solution methods, taking into account different friction angles along the wall and the rock face, can estimate the developed static or dynamic horizontal earth pressures behind vertical retaining walls experiencing various types of outward wall movements. The range of application of each proposed method, which is represented by the ratio of the distance between the wall and the rock face to the height of the wall, is compared with each other and also is examined for different wall friction angles as well as soil friction angles. Further, the result predicted by the modified Spangler - Handy solution method is compared with that from the experimental model test on sand. The comparison shows in general good agreements at various stages of retaining wall rotation about its toe. Finally results of analytical parametric study, together with the design charts, are presented to demonstrate the effects of wall friction angles and horizontal acceleration coefficients.

• Geotechnical Engineering
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• v.7 no.4
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• pp.75-88
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• 1991

A lot of landslides has occurred in rainy seasons beginning at June through September in Korea, where about 70 percent of the total area is mountaneous. Piles can be used as one of the most useful methods to stabilize such landslides. When a row of piles is installed in soil undergoing lateral movement such as landslides, the soil across the open space between the piles can be retained by the arching action of the soil. For the purpose to establish a reasonable design method for stabilizing piles, a method for stability analysis of the slope containing stabilizing piles is presented, using the theoretical equation of the lateral force acting on the piles in soil undergoing lateral movement. In particular, the theoretical equation is arranged by applying the coefcients of lateral force as a simple equation. And also the differential equations proposed in the previous studies for the pile-stability analysis are modified, assumming that the piles above the sliding surface shall be subjected to the lateral reaction from soil in proportion to the pile deflection. Finally, to investigate the effect of stabilizing piles against landslides, an existing landslide slope in Korea is adopted as an example.

• Geotechnical Engineering
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• v.7 no.4
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• pp.35-48
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• 1991

Based on centrifuge model tests, the failure mechanism of reinforced earth retaining wall under strip load was investigated in this paper. Tests were performed by changing the materials of reinforcing strips, strip lengths, and strip arrangements. The strips were strain-gauged to measure the tensions in strips. The results were analyzed and compared with various design methosds in use to verify their feasibility. Consequently, a centrifuge model test was an effective method of investigating the behavior of reinforced earth retaining wall. The 2 : 1 stress diffusion method showed comparable results with tests in estimating the capacity of the reinforced earth wall under strip load. The superposition of tensions due to selfweight of the backfill and strip load was valid to estimate total tensions mobilized in strips. Using the elasticity theory to estimate the maximum tension mobilized in strips due to surcharge, while solutions of Boussinesq and Westergaard underestimated less tensions than the measured valises, Frohlich solution showed the comparable results with tests.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.639-646
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• 2000

It is important to estimate the mechanical properties of clay since it is directly related to the design and the construction of geotechnical structures. Site exploration, which is composed of boring, sampling, in-situ, or laboratory tests, is preformed to estimate the mechanical properties. However, mechanical properties of clay measured from laboratory test may be different from in-situ properties due to disturbances occurred during sampling, transportation, storage, and trimming. In this study, the degree of disturbance according to sampling method was estimated with the test results of CK/sub o/U triaxial compression test on Yangsan clay. The soil samples were obtained by three types of sampling method, j.e., 76mm-tube sampler, 76mm-piston sampler, and block sampler. In order to evaluate the quality of samples, volumetric strain, undrained shear strength, secant Young's modulus, and pore pressure coefficient at peak measured from each sample were compared with one another. From the test results, it was observed that mechanical properties of the block and piston samples were more reliable than those of tube samples. But it was observed that the water content of piston was similar to that of tube samples at given depths while the water content of block samples was 14.3∼15.8% smaller than that of piston and tube samples. In addition to the evaluation of the quality of samples, relationship between c/sub u// σ/sub vc/'and OCR was established from the results of the CK/sub o/U triaxial compression tests, which were carried out using SHANSEP method. And also undrained shear strength was analyzed using the in-situ test data such as Cone Penetration Test(CPT), Dilatometer Test(DMT), and Field Vane Test(FVT) and was compared with that evaluated from CK/sub o/U triaxial compression test.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.37-48
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• 2004

This study is focused on the constitutive model in order to represent brittleness and dilatancy for cohesionless soils. The constitutive model was based on an anisotropic hardening rule derived from generalized isotropic hardening nile, which includes an appropriate hardening equation for the overall strain behavior at small to large strains. The yield surface is a simple cylinder type in stress space and it makes the model practically useful. Hence dilatancy behavior in cohesionless soils could be modeled reasonably. A peak stress ratio was defined in order to model brittle stress-strain relationships. An optimized design methodology was proposed on the basis of real-coded genetic algorithm in order to determine parameters for the proposed model systematically. The material parameters were then determined by that algorithm. In order to verify the proposed model, triaxial tests were performed under $K_0$ conditions far weathered soils. In comparison with the triaxial test results under $K_0$ conditions, the proposed model could calculate appropriately the actual effective stress behavior on brittle stress-strain relationships and dilatancy.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.87-98
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• 1999

Consolidation settlements on soft clay are often greatly and potentially damaging to structures. Currently, large-scale projects are in planning or progressing in Korea. These structures will be constructed on both thick and soft clay layers, and so the accurate evaluation of magnitude of settlement is required at every step in design and construction. Especially, secondary compression may play an important role in consolidation settlements of soft clay. Generally, the magnitudes of secondary compression are evaluated by laboratory and in-situ consolidation tests. The empirical $C_a/C_c$ may be economical, fast and powerful tool in estimating secondary consolidation settlement. However, the databases of the $C_a/C_c$ at construction site in Korea are insufficient. The purpose of this study is to investigate the relationship of $C_a/C_c$ on marine clay near the southern sea in Korea. A series of incremental loading consolidation tests (measuring base pore water pressure) is peformed. It was found that the $C_a/C_c$ on undisturbed marine clay is 0.0397.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.79-98
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• 1999

In the present study, a simple finite element method of analysis to predict non-uniform settlements at the interface between the mat foundation and foundation soils is proposed. Based on the proposed finite element method of analysis, the method to evaluate load sharing ratios of the foundation soils adjacent to the granular group piles is also presented. Further proposed is a procedure to estimate ultimate bearing capacity of the skirted granular group piles in a square pattern. To verify validity of the proposed methods and the estimated ultimate bearing capacity of the skirted group piles, comparisons are made with the results analyzed by using the PENTAGON3D FEM program. Finally, behavior characteristics with different reinforcement patterns of the skirts and the effect of an increase of ultimate bearing capacity due to the skirts are analyzed in connection with the design parameters.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.329-337
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• 2002

Based on the equivalent uniform stress concept presented by Seed and Idriss, sinusoidal cyclic loads which simplified the earthquake loads have been applied in evaluating the liquefaction resistance strength experimentally. However, the liquefaction resistance strength of soil based on the equivalent uniform stress concept can not exactly reflect the dynamic characteristics of the irregular earthquake motion. In this study, the criterion of the liquefaction resistance strength was determined by applying real earthquake loading to the cyclic triaxial test. From the test results, relationships between liquefaction behaviors of saturated sand and earthquake characteristics such as magnitude or time-duration were determined. Magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were also proposed.