• Journal of the Korean Geotechnical Society
• /
• v.17 no.5
• /
• pp.37-42
• /
• 2001

생석회말뚝공법은 연약점토에 대한 유용한 지반개량공법으로서 그 개량효과는 매우 빨리 나타난다. 본 연구에서는 생석회말뚝 타설 면적비에 따라 연약점토지반의 함수비나 전단강도 등의 특성이 어떻게 변화하는가를 규명하고자 하였다. 이를 위하여 철제상자에 연약점토로 모형지반을 조성하고 소요 면적비로 생석회말뚝을 타설한 후 적당한 시간간격을 두고 함수비와 전단강도를 측정하는 실내 모형시험을 수행하였다. 그 결과 면적비가 증가함에 따라 함수비의 감소량과 전단강도의 증가량은 커지지만 면적비가 약 10%를 초과하면 별 차이를 보이지 않으며 같은 면적비에서 생석회말뚝의 지름이 작고 간격이 좁으면 함수비의 감소량과 전단강도의 증가량은 더 크다는 것을 규명하였다. 또한 같은 양을 사용했다면 생석회말뚝공법보다 생석회혼합공법을 적용한 흙의 전단강도 증가량이 더 크다는 것을 알 수 있었다.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.3
• /
• pp.25-35
• /
• 2019

A laboratory test on uniaxial compressive strength was carried out by making 640 specimens in total, which were divided into two groups by their curing time of 7 and 28 days for 3 water content conditions of a water content at 100% saturation level and 10% and 20% increased water content from the state with clay, sand and gravel mixed grounds of 20 ground conditions of 4 types of stabilizer mixing conditions which were 8%, 10%, 12%, 14%, to understand laboratory strength characteristics for strength design of deep mixing ground. In case of clayey grounds, although the strength increased depending on the increase of stabilizer content, it showed to be analogous regardless of the curing time. And the impact on the strength development of deep mixing specimen according to water content was considered to be comparatively little compared to other grounds. For sandy grounds, the strength increment amount clearly showed to increase as stabilizer content increased, and also the increase of water content was determined to be decreasing the strength increment effect. For gravel mixed grounds, at 14% or over of stabilizer content, the effect on strength development was big making a large increase in strength, but compared to sandy grounds, the strength ratio depending on the curing time showed to be small.

• Journal of the Korean Geotechnical Society
• /
• v.16 no.2
• /
• pp.125-134
• /
• 2000

지반이 산업용 기름으로 오염될 때 지반의 강도변화 특성을 연구하기 위하여 모래와 실트질 모래 및 카오리나이트를 대상으로 함수비아 함유비를 변화시키며 다짐실험, 투수실험, 비배수상태에서 삼축압축실험을 실시하였다. 실험결과에 의하면 밀도가 같은 모래의 경우는 기름을 혼합하였을 경우가 물을 혼합하였을 경우에 비해 약 7%정도 전단 강도가 떨어지고 실트질 모래와 카오리나이트 경우는 기름을 혼합하였을 경우가 물을 혼합하였을 경우에 비해 점토입자와 기름의 화학적, 물리학적인 상호 작용으로 5~15%정도 강도가 증가하는 현상을 보였다. 일반적으로 산업용 기름 유출에 따라 토양오염 및 수질오염으로 동.식물에 큰 영향을 주고 있으나 토질역학적 거동은 초기 상태 및 모래에서는 전단 강도가 감소하였으나 점성토의 경우는 기름 유출 또는 유입에 따라 응집성, 부착성이 생겨 강도증가 현상을 가져와 큰 문제점이 없는 것으로 판단된다.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.8
• /
• pp.15-25
• /
• 2016

In order to analyze undrained shear strength for clayey silt with low plasticity from Hwaseong site, a series of laboratory and in-situ tests were performed. The Unconfined Compressive (UC) test and Simple Consolidated-Undrained Triaxial (SCU) test were examined in order to assess their applicability to the measurement of the undrained strength of this soil. In the case of clayey silt with low plasticity, although the samples were properly taken by undisturbed sampling method, the residual effective stress and the unconfined compressive strength were reduced considerably. Therefore, an effective confining pressure that corresponds to the typical marine clay should be applied to the soil specimen before shearing in order to compensate for the loss of residual effective stress. By evaluating the shear strengths of clayey silt with low plasticity as 75% of $s_{u(scu)}$, the in-situ shear strength of this kind of soil can be duplicated.

• Journal of the Korean GEO-environmental Society
• /
• v.10 no.6
• /
• pp.105-115
• /
• 2009

In this study, SPT, FV, and CPT tests were performed at five very soft grounds in southern coast of Korea to characterize the $S_u$ of very soft ground. In addition, a new modified SPT that is applicable to very soft ground was developed. Tests results showed that in very soft ground (N<2), the $S_u$ was lower than 12.5 kPa using the empirical N-Su correlation, and lower than 50 kPa and 65 kPa using vane shear test and CPT, respectively. It was shown that the results of in-situ tests were higher than those estimated from the N-Su correlation, and it was also demonstrated that the range of estimated $S_u$ was quite wide. New correlations that relate the modified SPT $N_m$ with Su from FV and CPT were developed, which are $S_u=1.76N_m-10.47$ and $S_u=1.82N_m-9.71$, respectively.

• Geotechnical Engineering
• /
• v.14 no.4
• /
• pp.103-116
• /
• 1998

To estimate pure shear strength, 150 sets of triaxial test data were analyzed. The proportional coefficient of shear strength($I_c$) at zero normal stress was nonlinearly decreased as failure coefficient m increases, while the internal friction $\phi_0$ at zero normal stress was nonlinearly increased. The ratio of shear strength $(c/\phi_0)$was inversely proportional to the ratio of the internal friction angles$(\phi/phi_0)$ The shear strength decreased as m increased, while internal friction angle increased. And uniaxial strength was proportional to $c,\phi$ Regression analysis showed that shear strength strongly affects m and $\sigma_c$ The proportional coefficient of shear strength was nonlinearly increased with RMR, while the internal friction angle $(\phi}$was linearly decreased.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.14 no.4
• /
• pp.23-28
• /
• 2010

This study evaluated the effect of vibration, level of lateral yielding strength, site conditions, ductility factor, strain-hardening ratio, and post-capping ratio of the strength limited bilinear SDF systems on the inelastic displacement ratio. The nonlinear response history analysis was conducted using 240 ground motions which were collected at the sites classified as site classes B, C, and D according to the NEHRP. To account for the P-$\Delta$ effects, this study considered negative stiffness ratios ranging from -0.1 to -0.5 of elastic stiffness. Four different damping ratios are used: 2, 5, 10, and 20%. From this study, an equation of inelastic displacement ratio was proposed using nonlinear regression analysis.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.169-179
• /
• 2003

Undrained shear strength of clay deposit is one of the most important properties in the design of geotechnical structures. The use of piezocone test is rapidly growing due to its merit that can measure the in-situ undrained shear strength continuously with less error. The reliability of the shear strength from piezocone test depends upon the cone factor applied. Many researchers have suggested different ranges of values for the factors. This study performs to find out the validity of the suggested values in Korea and their charateristics related to the mechanical properties of clay. Piezocone tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum Gyeongnam to investigate the charateristics of piezocone factors. The piezocone fators$(N_{kt}, N_{ke}, N_{\Delta u})$ based on the undrained shear strength from quick triaxial compression test are generally within the suggested range. And there appears considerable relations between undrained shear strength and $(N_{kt}, N_{ke}, N_{\Delta u})$ and between preconsolidation pressure and $(N_{kt}, N_{ke})$, while plasticity index, rigidity index and friction ratio do not show any relations with cone factors. The results also reveal that factor $(N_{\Delta u})$ shows higher reliability than factors $(N_{kt} and N_{ke})$, which show smaller standard deviation, breadth of change and scattering.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1996.10a
• /
• pp.285-294
• /
• 1996

• Journal of the Korean Geotechnical Society
• /
• v.21 no.9
• /
• pp.53-64
• /
• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.