• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.43-52
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• 1984

This paper is concerned with the strain characteristics of the time effect on the remoulded saturated day sampled from the downstream of the Yeongsan river, and the constitutive equation that can generally explain time-dependent behaviors of norma1ly consolidated clay. This paper examines whether or not the afore-said constitutive equation can be applied to the remoulded Mooan-clay. Throughout this study, the conclusions obtained are as follows. 1. Throughout the isotropic consolidation test for 7 days and the isotropic relaxation test, the existence of the static and dynamic yielding surfaces is confirmed respectively. 2. The characteristics of time effect of the deformation, namely, the existence of a unique stress-strain-time relation, is conformed from the experimental result on the Mooan-clay. 3. The prodictions of the stress path and the strain on the Cam-clay theory is not consistent with those observed during the experiments. 4. Constitutive equation(2-3-12) obtained by applying Cam-clay theory to Perzyna's elastic-viscoplasticity theory can explain the behavior of pore water pressure during isotropic stress relaxation, concerned with time dependency under undrained condition. The equation can also explain the results of the undrained triaxial compression test for the clay with different strain rate under the same or different consolidation history. 5. This constitutive equation has eight material parameters which can be determined from triaxial compression tests.

• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.65-74
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• 2014

Cemented soils have been widely used in road and dam construction, and recently ground improvement of soft soils. The strength of such cemented soils can be tested by using cored sample or laboratory-prepared specimen through unconfined compression or triaxial tests. It takes time to core a sample or prepare a testing specimen in the laboratory. In a certain situation, it is necessary to determine the in-situ strength of cemented soils very quickly and on time. In this study, the relation between unconfined compressive strength and shear wave velocity was investigated for predicting the in-situ strength of cemented soils. A small cemented specimen with 5 cm in diameter and 10 cm in height was prepared by Nakdong river sand and ordinary Portland cement. Its cement ratios were 4, 8, 12, and 16% and air cured for 7, 14, and 28 days. For recycling of resources, a blast furnace slag was also used with sodium hydroxide as an alkaline activator. The shear wave velocity for cemented soils was measured and then unconfined compressive strength test was carried out. As a cement ratio increased, the shear wave velocity and unconfined compressive strength increased due to increased density and denser structure. The relation between unconfined compressive strength and shear wave velocity increased nonlinearly for cemented soils with less than 16% of cement ratio.

• Journal of the Korean GEO-environmental Society
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• v.16 no.1
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• pp.45-53
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• 2015

This study has obtained Soil Water Retention Curve (SWRC) of the unsaturated soil from the volumetric pressure plate extractor test and the triaxial compression tests was also conducted. By using the rainfall data measured in the site the seepage analysis of unsteady flow was performed with the program of SEEP/W in Geostudio 2007 and stability of the slope was analyzed with SLOPE/W program. Results of analyses show that shear strength of the unsaturated soil increases with the increase of matric suction. And it was also found that the net volumetric stress and the apparent cohesion increased with the matric suction. The seepage analysis of rainfall represents that the increasing rate of negative pore pressure at the zone of large negative pore pressure is appeared to be high even though lower rainfall intensity, but this tendency declines with ground depth. The stability analysis of slope was carried out for the actual plane of failure with the data representing the field condition. The factor of safety thus calculated was about unity (1.0) or just below, which means that the adopted method of analysis is in good agreement with the field condition.

• Journal of the Korean GEO-environmental Society
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• v.11 no.1
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• pp.13-18
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• 2010

It is crucial to decide reasonably the parameters necessary for design through research on the characteristics of rock in order to analyze stability of rock structure. This article has conducted both pressure meter test, uniaxial and triaxial compression test to the areas of andesite or tuff located in local regions such as Yeosu, Gwangju, Yangsan, Busan, and Daejeon and has comparatively analyzed previously proposed estimative formulas. According to the result of estimating the deformation modulus through using the damping coefficient suggested by Nicholson & Bieniawski, when RMR is less than 60, it is desirable to use the result of the pressure meter test considering the damping coefficient. If the RMR value is over 60, however, the formula suggested by Kim Gyo-won has been proved to be the most applicable. Moreover, according to the result of comparing the RMR, adhesion, and angle of internal friction, both the adhesion and angle of internal friction best correspond to the formula proposed by Tsuchiya. Comparatively analyzing the relations between the rock deformation modulus and RMR and also suggesting the formula of calculating the shear strength parameter to use the RMR value, this study did not include the deformation modulus and shear strength parameter as factors to decide the RMR index. Since result can differ by several factors, it will be necessary afterwards to suggest practical estimative formulas applicable to the actual spots of Korea.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.151-160
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• 1999

A series of laboratory tests for the marine clay sampled under the sea of Kwangyang bay have been conducted. The main types of tests are the general index property tests, the oedometer tests and the triaxial compression tests in both undrained(CIU) and drained(CID) conditions. The clayey samples, classified as CL, CH with natural water content of 38.3~84.6% and liquidity index of 0.71~0.98, are in the normally consolidated state with O.C.R. of 1.0l~l.60. The undrained stress path from CIU tests can be normalized with isotropic consolidation pressure$(p_0)$ and equal shear strain contour is linear passing through the origin in the (q, p) plot. The undrained shear strain is found to be the only function of the stress ratio($\eta$) and linear with intercept in the ($\varepsilon/\eta,\eta$) plot. The built-up pore pressure normalized with pc is also linear with respect to $\eta$. and its slope is defined by ´C´ as a pore pressure parameter. Equations to predict the undrained stress path and the shear strain are proposed. It is proved that the proposed equations give better agreements to the measured values than the Cam-clay theories. The failure points of the stress path are located on the same C.S.L. in (q, p) plot during both CIU and CID tests, which justifies the concept of critical state theory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1C
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• pp.39-51
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• 2011

A large number of small particles may surround large gravels which are non-contact and dispersed within the ground. The strength of such soil may be influenced by the mechanical properties of a few coarse gravels. A specimen or gravel size can impact the shear characteristics of sand with dispersed gravels. In this study, the size of gravel and specimen varies and its effect on shear characteristics of a granular soil was evaluated. Five sizes of gravels with 7, 12, 15, 18, and 22 mm were used repeatedly and inserted in the middle of each compacted layer. A specimen consists of five or ten equal layers depending on gravel size, which is 5 cm or 10 cm in diameter and 10 cm or 20 cm in height. An embedded gravel ratio by weight is 3% and constant for all cases with gravel. After consolidation, a series of undrained triaxial compression tests under three confining pressures was performed on sand with dispersed gravels. The maximum deviator stress of a specimen with 10 cm in diameter was at average 30% higher than that with 5 cm in diameter and increased up to 90% for a specimen with gravel. When a gravel size of 7 and 12 mm used, the maximum deviator stress of a specimen with 10 cm in diameter was higher than that of one without gravel, whereas the maximum deviator stress of a specimen with 5 cm was higher or lower than that without gravel. The gravel size and specimen diameter influenced the undrained behavior of sand. The maximum deviator stress of a specimen with gravel either increased or decreased compared to that without gravel, depending on the ratio of gravel size to specimen diameter, 1/5.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.146-152
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• 2018

In this study, to improve the performance of asphalt mixtures for plastic deformation occurring mainly in Korea, complex modifiers were prepared by mixing powders and liquid type modifiers. The main constituents were powdery diatomaceous earth, mica and carbon black, and liquid type solid 70% SBR latex. The tensile strength ratios for the two asphalt mixtures used in the test were above 0.80 for the Ministry of Land Transportation (2017) asphalt mixture production and construction guidelines. The effects of increasing the tensile strength in the dry state was more than 14% when the composite modifier was added. The deformation rate per minute by the wheel tracking test load was an average of 0.07 to 0.147 for each mixture. The strain rate per minute was improved by the modifier, and the dynamic stability was improved by almost 100% from 295 to 590. In addition, the final settling was reduced from 11.38 mm to 9.57 mm. A plastic deformation test using the triaxial compression test showed that the amount of deformation entering the plastic deformation failure zone at the end of the second stage section and in the third stage plastic deformation section was 1.76 mm for the conventional mixture and 1.50 mm for the complex modifier mixture. The average slope of the complex modifier asphalt mixture mixed with the multi-functional modifier was 0.005 mm/sec. The plastic deformation rate is relatively small in the section where the road pavement exhibits stable common performance, i.e. the traffic load.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.188-197
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• 2010

This paper presents experimental results of a series of 1-g shaking table model tests performed on end-bearing single piles and pile groups to investigate the effect of particle size on the dynamic behavior of soil-pile systems. Two soil-pile models consisting of a single-pile and a $4{\times}2$-pile group were tested twice; first using Jumoonjin sand, and second using Australian Fine sand, which has a smaller particle size. In the case of single-pile models, the lateral displacement was almost within 1% of pile diameter which corresponds to the elastic range of the pile. The back-calculated p-y curves show that the subgrade reaction of the Jumoonjin-sand-model ground was larger than that of the Australian Fine-sand-model ground at the same displacement. This phenomenon means that the stress-strain behavior of Jumoonjin sand was initially stiffer than that of Australian Fine sand. This difference was also confirmed by resonant column tests and compression triaxial tests. And the single pile p-y backbone curves of the Australian fine sand were constructed and compared with those of the Jumoonjin sand. As a result, the stiffness of the p-y backbone curves of Jumunjin sand was larger than those of Australian fine sand. Therefore, using the same p-y curves regardless of particle size can lead to inaccurate results when evaluating dynamic behavior of soil-pile system. In the case of the group-pile models, the lateral displacement was much larger than the elastic range of pile movement at the same test conditions in the single-pile models. The back-calculated p-y curves in the case of group pile models were very similar in both sands because the stiffness difference between the Jumoonjin-sand-model ground and the Australian Fine-sand-model ground was not significantly large at a large strain level, where both sands showed non-linear behavior. According to a series of single pile and group pile test results, the evaluation group pile effect using the p-multiplier can lead to inaccurate results on dynamic behavior of soil-pile system.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.27-35
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• 2004

Most of concrete fatigue tests currently used are flexural tension or compression methods to investigate the tensile or compressive properties, respectively. However, the concrete pavement or concrete slab is actually subjected to a combined stress condition such as biaxial or triaxial. The split tension test may result in similar stress condition to biaxial stress condition. The purposes of this study were to evaluate the split tension fatigue test method for application in concrete. These were done by a finite element analysis and experimental series. The results were as follows: The optimum configuration of split tension fatigue test was a cylinder of 15cm in diameter and 7.5cm in thickness, which had a little different thickness compared to the KS standard cylinder of ${\phi}15{\times}30cm$. The concrete stress ratio of compressive against horizontal from FEA was 3.1, while that from theory was 3.0. The stress distributions of mortar and steel were almost similar at different thicknesses. The measured static split tensile strengths of concrete and mortar were quite similar at 30cm and 7.5cm thickness cylinders. The measured stress-strain relationship showed their consistency at all specimens regardless of thickness, and confirmed the results from FEA. As a results, the concrete split tension specimen, cylinder of 15cm in diameter and 7.5cm in thickness, could be used at fatigue test because of its accuracy, simplicity and convenience.

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