• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.57-67
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• 1999

In conventional stability analysis of embankment on soft clay ground, an averaged undrained shear strength$(s_u)$ for the depth of clay layer is usually used. Also, all applied load is assumed to an immediate load for simplicity of analysis. The load in the field, however, increases gradually. Undrained shear strength increases during loading due to consolidation of clay ground. In this study, the stability analysis program(RSI-SLOPE) is developed. By using this program, it is possible to consider the rate of strength increase according to the elapsed time of consolidation and the depth of clay ground. And the rested duration for consolidation and gradually increased load can also be considered. Using the examples of some embankments, the critical embankment heights calculated by RSI-SLOPE program are compared with those by PCSTABL without the considerations of gradually increased load and rate of strength increase. In addition, this study contains analysis and comparison about the influence of coefficient of consolidation$(c_u)$ and drainage distance$(H_{DR})$ in the embankment design. RSI-SlOPE program may be useful for more effective and accurate embankment design.

• Journal of the Korean GEO-environmental Society
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• v.2 no.3
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• pp.47-56
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• 2001

In the present study, mainly to determine the embarkation time of equipment in dredged clay fills, an analytical approach is performed to predict a variation of the undrained shear strength in the outermost layer. In this approach, Gibson's non-dimensional linear constant defining the relationship between the void ratio and the effective stress is employed. Also in this approach, void ratios and settlements associated with the volume change due to the self-consolidation and the desiccation shrinkage are evaluated at various elapsed times based on the finite difference solution technique proposed by the authors(1999) and the developed computer program named as DSCON. Predicted results(water content ratio, unit weight and undrained shear strength) are compared with those of laboratory model tests conducted with soil samples obtained from the Koheung site. Based on the predicted undrained shear strengths, possible embarkation time of a equipment is also evaluated. In addition, further analyses are made to indirectly verify the efficiency of the analytical approach proposed in the present study using the PSDDF computer program which can consider the drainage efficiency.

• Ocean and Polar Research
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• v.25 no.spc3
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• pp.353-360
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• 2003

Estimation of undrained shear strength $(S_u)$ of clayey soils from piezocone penetration test (CPTu), which has widely been known as one of very promising in situ test methods, requires piezocone factors. Empirical correlations are generally utilized to derive piezocone factors, but previous studies on the empirical piezocone factors are site-specific and in some cases need engineering characteristics, which should be obtained from additional laboratory tests. In this study, empirical cone factors were evaluated by comparing 6 CPTu results at Shihwa region in Korea with reference $S_u$ values obtained from field vane test (FVT). From previous CPTu results of other regions in Korea as well as the results herein, the correlations between piezocone factor, $N_{kT}$ and CPTu results were investigated and three simplified evaluation methods of $S_u$ using only CPTu results were presented. The $S_u$ values estimated by $(q_T-{\sigma}_v)/{\sigma}'_v$ method shows better matches with those obtained from laboratory tests for marine clays at Shihwa region.

• Journal of the Korean GEO-environmental Society
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• v.12 no.8
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• pp.13-24
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• 2011

In the part of geotechnical engineering, soils are classified as either the coarse grained soil or the fine-grained soil following the fine content($F_c$=50%) according to the granularity, and appropriate design codes are used respectively to represent their mechanical behaviour. However, sand-clay mixtures, which are typically referred to as intermediate soils, cannot be easily categorized as either sand or clay. In this study, several monotonic undrained shear tests were carried out on Silica sand fine mixtures with various proportions, and a wide range of soil structures, ranging from one with sand dominating the soil structure to one with fines controlling the behaviour, were prepared using compaction method or pre-consoldation methods in prescribed energy. The shear strength of mixtures below the threshold fines content is observed that as the fines content increases, maximum deviator stress ratio decrease for dense samples while an increase is noted for loose samples. Then, by using the concept of fines content and granular void ratio, the monotonic shear strength of the mixtures was estimated. It was found that the shear behavior of mixtures is greatly dependent on the skeleton structure of sand particles.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.681-686
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• 2006

This study is to examine slope activity safety ratio on the strength of the natural sample or soil collected through field test in the slope activity region during destruction happened in the course of soil-relocating work planned for ground improvement under strict supervision at the house-building site, using Bishop's slope analysis method and investigate relationship between slope analysis theories and actual destruction so as to compare determining method of clean water of soil essential for slope activity analysis and accuracy of resulting value of clean water of soil.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.93-101
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• 2017

In this study, a subjective weighting factors were awarded based on some indication of the difficulty of assessing the preconsolidation stress using traditional methods (Casagrande, Onitsuka et al., Silva, Becker et al., Janbu and Karlsrud methods) such as those proposed by Casagrande and Janbu using undisturbed sample obtained from Gwangyang dredged clay with high plasticity located in the southern area of Korean peninsular. These numbers only assess the relative ease of finding preconsolidation stress and say nothing regarding the accuracy of the value. The data were compared with measurements of undrained shear strength using strength incremental ratio, checking where or not the values are in the range of 0.25 to 0.35 (typical values of Korean marine clay) and analyzing standard deviation(degree of variability). The measurements of undrained shear strength were obtained from unconfined compression tests (UCT). When determining preconsolidation stress of Korean marine clay, at first, the work method proposed by Becker et al. and the bilogarithmic method proposed by Onitsuka et al. should be used. In addition, preconsolidation pressure should be estimated using the traditional Casagrande method as a basic of comparison.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.181-194
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• 2013

Landslides are known as gravitational mass movements that can carry the flow materials ranging in size from clay to boulders. The various types of landslides are differentiated by rate and depositional features. Indeed, flow characteristics are observed from very slow-moving landslides (e.g., mud slide and mud flow) to very fast-moving landslides (e.g., debris avalanches and debris flows). From a geomechanical point of view, shear-rate-dependent shear strength should be examined in landslides. This paper presents the design of advanced ring-shear apparatus to measure the undrained shear strength of debris flow materials in Korea. As updated from conventional ring-shear apparatus, this apparatus can evaluate the shear strength under different conditions of saturation, drainage and consolidation. We also briefly discussed on the ring shear apparatus for enforcing sealing and rotation control. For the materials with sands and gravels, an undrained ring-shear test was carried out simulating the undrained loading process that takes place in the pre-existing slip surface. We have observed typical evolution of shear strength that found in the literature. This paper presents the research background and expected results from the ring-shear apparatus. At high shear speed, a temporary liquefaction and grain-crushing occurred in the sliding zone may take an important role in the long-runout landslide motion. Strength in rheology can be also determined in post-failure dynamics using ring-shear apparatus and be utilized in debris flow mobility.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.259-267
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• 2001

실내시험으로 구한 점토의 공학적 성질은 샘플링, 운반, 저장, 그리고 성형과정 동안에 발생하는 시료의 교란으로 인해 원지반의 성질과 다르게 측정된다. 본 연구에서는 양산점토에 대한 삼축압축시험($CK_{o}$ UC) 결과를 이용하여 샘플링 방법에 따른 교란의 정도를 평가하였다. 실험에 사용된 시료는 76mm 튜브샘플러, 76mm 피스톤샘플러, 블록샘플러로 채취되었으며, 시료의 교란정도를 평가하기 위해 각 시료에서 측정된 체적변형률, 비배수 전단강도, Secant Youngs modulus, 그리고 파괴시 간극수압계수를 비교하였다. 시료의 교란정도를 평가하는 것 이외에도 SHANSEP 방법을 이용하여 수행한 $CK_{o}$ U 삼축압축시험 결과를 이용하여 양산점토에 대한 정규화 전단강도($C_{u}$ /$\sigma$$_{vc}$ )와 OCR 관계를 규명하였다. 또, 피에조콘 관입시험, 딜라토메타 시험, 그리고 현장 베인시험결과를 이용하여 구한 양산점토의 비배수 전단강도를 삼축압축시험 결과와 비교하였다.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.93-102
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• 2003

Unconfined compression test (UC) has been widely used to determine the undrained shear strength ($c_u$) of clay, because it is convenient and economical. However, UC can not represent the behaviour of in-situ stress condition and the strength obtained by the test is generally underestimated compared to that of triaxial compression, due to no confining pressure. Therefore, a simple and practical method to correct the ($c_u$) for sample disturbance and to be used in geotechnical practice is needed. This study is aimed at proposing the method to estimate in-situ undrained shear strength from UC with suction measurement. The proposed method is based on theoretical shear strength equation of perfect sample (Noorany & Seed, 1965), and effective overburden stress and analysis results ($A_f,\phi'$) of effective stress behaviour by UC are needed for the equation. The shear resistance angle ($\phi'$) can be simply estimated through the result that $K_f$-line slope of the UC is 1.6 times higher than that of triaxial compression test. The result of this study shows that the measured strength by this method is very similar to that of the undrained shear strength by triaxial compression test (CK$_0$UC).

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.41-49
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• 2005

Recently, ground has been often exposed to high temperature environments such as chemical ground improvement, thermal energy storage system, and underground nuclear waste disposal system. Since the behavior of clay is sensitive to temperature change, the studies on the engineering properties of clay subjected to high temperature history may be important. This paper presents the mechanical behavior of clay with high temperature condition. $\bar{CU}$ tests using a high temperature and pressure triaxial compression test apparatus were carried out in order to investigate characteristics of deformation, shear strength, compression and consolidation of clay. During tests, the temperature was varied from $20^{\circ}C,\;50^{\circ}C,\;75^{\circ}C,\;80^{\circ}C\;to\;100^{\circ}C$.