• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.15-26
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• 2004

Based on an estimating method for post-cyclic strength and stiffness with cyclic triaxial tests proposed by one of the authors, cyclic 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 cyclic and post-cyclic DSS tests were interpreted by a modified method as adopted for cyclic and post-cyclic triaxial tests. In particular, influence of plasticity index for fine-grained soils and initial static shear stress (ISSS) was emphasised. Findings obtained from the present study are: (i) liquefaction strength ratio of fine-grained soils decreases with decreasing plasticity index and increasing ISSS; (ii) plasticity index and ISSS did not markedly influence relation between equivalent cyclic stiffness and shear strain relations; (iii) the higher the plasticity index of fine-grained soils is, the less the strength ratio decreases with increment of a normalcies excess pore water pressure (NEPWP); (iv) stiffness ratio of plastic silt has large activity decrease rapidly with increasing excess pore water pressure; and (v) 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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• 2003.03a
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• pp.569-576
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• 2003

Based on the equivalent uniform stress concept Presented by Seed and Idriss, sinusoidal cyclic loads which simplified 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. The liquefaction assessment method which was invented by using the equivalent uniform stress concept is suitable for the severe earthquake region such as Japan or USA, so the proper method to Korea is needed. In this study, estimation of the resistance to liquefaction was conducted by applying real earthquake loading to the cyclic triaxial test. From the test results, the characteristics of the fine sand under moderate earthquake were analyzed and compared with the results under strong earthquakes. Typically real earthquake loads used in this study are divided into two types - impact type and vibration type. Furthermore, results of the liquefaction resistance strength based on the equivalent uniform stress concept and tile concept using real earthquake loading were compared.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.916-923
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• 2005

In this study, to observe aging effect of undrained shear behavior for Nak-Dong River sand, undrained static and cyclic triaxial tests were performed with changing relative density ($D_r$), consolidation stress ratio($K_c$) and consolidation time. As a result of the test, the modulus of elasticity to all samples estimated within elastic zone by the micro strain of about 0.05% in case of static shear behavior increased with the lapse of consolidation time significantly, so aging effect was shown largely. Also strength of phase transformation point(S_{PT}$) and strength of critical stress ratio point($S_{CSR}$) increased with the lapse of consolidation time. Undrained cyclic shear strength($R_f$) obtained from the failure strain 5% increased in proportion to relative density($D_r$) and initial static shear stress($q_{st}$), $R_f$ of consolidated sample for 1,000 minutes increased about 10.6% compared to that for 10 minutes at the loose sand, and $R_f$ increased about 7.0% at the medium sand. In situ application range of $R_f$ to the magnitude of earthquake for Nak-Dong River sand was proposed by using a increasing rate of $R_f$ as being aging effect shown from this test result.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.67-74
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• 2002

An experimental assessment on the dynamic behavior of saturated sand which can consider the irregular characteristics of earthquakes was proposed. The equivalent uniform stress concept presented by Seed and Idriss has been applied to evaluate the liquefaction resistance strength to simplify earthquake loading. However, it was known that the liquefaction resistance strength of soil based on the equivalent uniform stress concept can't exactly mirror the dynamic characteristics of the irregular earthquake motion. In this study, estimation of 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 excess pore water pressure and the earthquake characteristics such as magnitude or duration were determined. Magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were also proposed.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1126-1133
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• 2005

The effects of mean particle size and uniformity coefficient of dredged soils to the liquefaction resistance strength and dynamic characteristics are experimentally studied in this paper. Representative 4 mean particle sizes and 3 uniformity coefficients were selected and 12 representative particle size distribution curves which have different mean particle sizes and uniformity coefficients, were artificially manufactured using the real dredged river soil. Cyclic triaxial tests and torsional shear tests were carried out to analyze the effect of mean particle size and uniformity coefficient to the liquefaction resistance strength and dynamic characteristics of soils.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.129-136
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• 2001

본 논문에서는 석탄회 매립지반의 액상화 가능성을 평가하기 위해 순수 모래시료와 더불어서 모래시료와 석탄회가 혼합된 모래시료에 대한 일련의 진동삼축실험을 변형률제어 방법으로 수행하였다. 실험결과 진동하중에 의해서 시료 내에 발생하는 간극수압의 크기는 작용하는 전단변형률의 크기에 심각하게 영향을 받고, 작용하는 전단변형률이 지반의 한계전단변형률 보다 작은 경우에는 진동수가 높은 조건에서도 간극수압이 발생하지 않음을 알았다. 또한 전단변형률이 약 0.1%보다 작고 한계전단변형률에 가까운 경우에는 순수 모래시료와 비교하여 본 논문에서 조사한 석탄회 함유율 범위 (10%~30%)의 시료에서 간극수압이 더 크게 발생하였다. 반면에, 전단변형률이 큰 경우에는 순수 모래시료에서 간극수압이 크게 발생하는 추세를 보였다. 반복 전단에 따른 간극수압의 발생량은 전반적으로 석탄회 함유율이 증가할수록 커지는 경향을 보였다. 이러한 결과를 근거로 해안이나 하천에 인접한 한계지 개발에 있어서 사질토에 석탄회를 혼합 매립하여 지반을 조성하는 경우에 액상화에 대해서 불안정한 지반이 될 가능성이 있는 것으로 판단되었다.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.47-55
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• 2009

This research has the purpose to examine the potential of shell, a byproduct of maritime products to be utilized as alternative environment-friendly construction material by mixing and applying it with residual soit which is used as burial or filling material to recycle it. To that end, the research looked into the mechanical characteristics of shell through cyclic triaxial test by mixing it with residual soil. With the mixing ratios of shell of 5 groups set at 5.0%, 10.0%, 20.0%, 40.0% and 60.0%, the mixture soils was processed through a series of cyclic triaxial tests. And it was shown that liquefation resistance has limitation in the mixed soils with shell substitute content ratios exceeding 20.0%. To increase the liquefaction resistance of the mixed soil, this research has shown that addition of moderate amount of glass fibers would suffice.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.43-51
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• 2014

In the earth structures of railways, large coarse granular materials are widely used as fill materials. However, experimental studies that consider the dynamic properties of these coarse granular materials have rarely been carried out in Korea due to the lack of a large scale test apparatus in this country. In this study, large scale cyclic triaxial tests were carried out for materials such as reinforced roadbed (subballast, graded crushed stone), transition zone gravel, and the upper subgrade of a railway. These specimens were prepared according to certain conditions (dry unit weight, grain size distribution, and so on) specified in the Korea railroad design standard. Based on these large triaxial test results, normalized shear modulus and damping ratio curves according to small strain level are suggested. A model and coefficients for each material are also proposed.

• Geotechnical Engineering
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• v.2 no.1
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• pp.7-14
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• 1986

The structure of the collapsible soils, such as decomposed granite soil and loess, were examined by the odeometer test, SEM & XES analysis and static & cyclic triaxial test, and hove this structure have influences upon the collapsible behaviour under static and cyclic load was investigated. The study results obtained are as follows; 1. The macropores space of decomposed granite soil (rd=1.50g/cm3) and loess (rd=1.43g/cm3) used in this test were well developed, and showed the behaviour of collapsible soil. 2. Collapsible soil has high resistance on the strain under natural moisture content, however, the resistance on the strain was sharply decreased by the absorption and increasing load since its special structure was destructed. 3. Under the static load, the strain of collapsible soil was high by the viscous flow of the cyclic bonds with time lapse, but Infer the cyclic load, the strain of collapsible soil was low since the tinge needed to destruct the bonding force of clay was not enough. 4. The understanding about the cyclic behaviour of collapsible soil may be helpful to predict the elastic & residual strain of the foundations by the earthquake together with the damage by the additional failure.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.73-85
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• 2002

This paper is focused on studying the undrained cyclic triaxial behavior of saturated Nak-dong River sand, using anisotropically consolidated specimens. A test of isotropically consolidated specimens was performed to compare the results of the anisotropically consolidated specimens. The cyclic shear stre3ngth of the sand under various combinations of initial static shear stress and relative density was considered. Failure was defined as a 5% double amplitude cyclic strain and a 5% residual axial strain for both reversal stress and no reversal stress conditions. Using this definition, the cyclic strength of the anisotropically consolidated specimens was affected by the initial static shear stress. For anisotropically consolidated Nak-dong River dense sand, the cyclic strength is greater than that of Toyolura silica sand but is smaller than that of Dogs Bay carbonate sand. By comparing the experimental and predictecl results, it was possible to predict the residual pore pressure of Nak-dong River sand using Hyodo's model with initial static shear stress subjected cyclic loading.