• The Journal of Engineering Geology
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• v.23 no.3
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• pp.247-256
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• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.45-55
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• 2008

CFRD (Concrete Faced Rockfill Dam) has been world-widely constructed due to a lot of advantages which it has compared with rockfill dam and recently, sand/gravel materials, Instead of crushed rock materials, are also utilized as a main rockfill material to overcome geological and environmental problems. In Korea, two dams using sand/gravel materials as a main fill material were designed and are being constructed. In this research, the strength and deformation characteristics of the rockfill and sand/gravel materials taken from 2 dam sites were tested by using a laboratory large triaxial testing equipment for a total of 7 cases. From the results of large triaxial and compaction tests, it was observed that two kinds of materials show a little different compaction, shear strenght and deformation characteristics. It could be expected that the shear strength of sand/gravel material was not disadvantageous compared with that of rockfill materials, however, there was some difference between two materials with respect to behavior characteristics. On the other hand, smaller displacements were observed from numerical analysis based on the data from a large triaxial test when the sand/gravel is used as a main fill material compared with the case when the crushed rock material is used as a main fill material. Finally, in spite of a little different shear strength and behavior characteristic between two materials, it was concluded that it will not lead to a significant problem when the sand/gravel material is used as a main rockfill material.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1115-1122
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• 2011

Reinforced-Roadbed materials are usually composed of crushed stones. Repeated load application can induce deformation in the reinforced-roadbed layer so that it causes irregularity of track. Thus it is important to develop a prediction model of elastic modulus based on stress-strain relation under repeatitive load in order to investigate behavior of reinforced roadbed. The prediction model of elastic modulus of the material can be obtained from repeated triaxial test. However, a proper size of the sample for the test must be used. In this study, a large repeatitive triaxial test apparatus with the sample size of diameter of 30 cm and height of 60cm was adapted for performing test of the crushed stone reinforced-roadbed considering large particle size to get resilient modulus Mr. The obtained resilient modulus was compared to shear modulus obtained from mid size resonant column test. The sample size effect is somewhat large enough so that it is required to design a scale factor based on similarity law in order to use smaller samples for getting elastic modulus of the crushed stone reinforced-roadbed material. A scale factor could be obtained from this study.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.61-71
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• 2005

Cemented Sand and Gravel (CSG) is a material made by simple mixing of rock-based raw materials such as excavated soil and riverbed gravel together with cement and water. The use of CSG material for cofferdam and large dam is gradually increasing in Japan because a quarry and aggregate plants can be diminished. Also, the CSG method can reduce dam construction cost, construction duration and destruction of environment. In this paper, the basic strength characteristics of CSG, such as compressive strength, modulus of elasticity and stress-strain curve were investigated by unconfined compression test and large triaxial compression test. From the results of the experimental study, the correlation equations between elastic modulus and unit cement, age are proposed.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.27-37
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• 2006

Cemented Sand and Gravel (C.S.G) method has become increasingly popular in Japan and throughout the world as a construction method and material. This method is favorably used for cofferdam and large dam because a quarry and aggregate plant facility can be diminished. Also, this method can reduce construction cost, work duration and destruction of environment. In this paper, a methodology for C.S.G mix design based on so-called soil mechanics approach is proposed for trapezoid-shaped dam. The methodology consists of selection of a suitable aggregate, introduction of compaction method, processing to prepare standard specimens, and determination of mix portions. Also, unconfined compressive strength tests and large triaxial compression tests are performed. From the results of the test, correlation equation among strength, elastic modulus and unit cement is proposed.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.81-94
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• 2007

In most experimental researches on the liquefaction phenomenon, an earthquake as a random vibration has been regraded as a sinusoidal wave or a triangular wave with an equivalent amplitude. Together with the development in the part of signal control and data acquisition, dynamic experimental equipments in the soil dynamics have also developed rapidly and further more, several real earthquakes have been simulated in the large model test such as shaking table tests and centrifuge tests. In Korea, several elementary laboratory tests to simulate the real earthquake load were performed. From these test results, it was reported that the sinusoidal wave cannot reliably reflect the soil dynamic behavior under the real earthquake motion. In this study, 4 types of dynamic motions such as the sinusoidal wave, the triangular wave, the incremental triangular wave and several real earthquake motions which were classified with shock-type and vibration-type were loaded to find something new to explain the change of the excess pore water pressure under the real earthquake load. Through the detailed investigation and comparison on all test results, it is found that the dynamic flow is generated by the soil plastic deformation and the velocity head of dynamic flow is changed the pressure head in the un-drained condition. It can be concluded that the change of the excess pore water pressure is related to the pressure head of dynamic flow. Lastly, a new hypothesis to explain such a liquefaction initiation phenomenon under the real earthquake load is also proposed and verified.

• Journal of the Korean Geosynthetics Society
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• v.8 no.4
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• pp.27-34
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• 2009

In this paper, characteristics of shear strength and deformation of geosynthetics-reinforced slag materials are described. In order to investigate the effect of geosynthetics on shear strength and deformation behavior of slags, when they are reinforced with geosynthetics or geomat such as PET mat, large triaxial tests were performed under consolidated-drained condition. The materials used in the study are real ones as they are in the field, so that the scale effect of samples disappeared. From the large triaxial tests, it was observed that the stress-strain relationship of geosynthetics-reinforced slags shows relatively small dilatancy and weak tendency of strain hardening, compared with that of slags without reinforcement. The shear strength parameters such as apparent cohesion and internal friction angle increase with PET mat reinforcement, consequently result in about 1.2 (for low confining pressure) to 1.4 (for high confining pressure) times of shear strength of un-reinforced sample. Therefore, the adoption of geomat-reinforced slag layers leads to an increase in the factor of safety for embankment design on soft soil formations.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.1-9
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• 2007

The purpose of this study is to carry out the quantitative sensitivity analysis on rockfill material influencing the dam crest displacement of CFRD(Concrete-Faced Rockfill Dam) subjected to earthquake loading. The total 105 dynamic numerical analyses (2 input earthquake, 2 magnitudes for each earthquake. 27 rockfill material property combinations obtained from large triaxial tests) on CFR type "D" dam in operation were conducted. The global sensitivity analysis was carried out using the results of numerical analysis. From the results of sensitivity analysis, It was found that the crest settlement of the CFR type dam subjected to earthquake was absolutely affected by the shear modulus of rockfill material irrespective of the input earthquakes and the maximum acceleration of each earthquake. Also, it was found that the horizontal displacement of the dam crest was highly affected by the shear modulus of rockfill material though the extent of effect on that was smaller than the settlement and the extent of effect depended on the input earthquakes and the maximum acceleration of each earthquake. On the contrary, it was found that the effect of friction angle was negligible.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.73-83
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• 2006

The behaviour characteristics of Granular Compaction Pile (GCP) are mainly governed by the lateral confining pressure mobilized in the soft soil matrix to restrain the bulging failure of the granular compaction pile. The GCP method is most effective in soft soil with undrained shear strength ranging $15{\sim}50kPa$. However, the efficiency of this method reduces the more compressible soil conditions, which does not provide sufficient lateral confinement. In the present study, the GCP method reinforced with uniformly graded permeable concrete is suggested for the extension of application to the soft ground. Also, large triaxial compression tests are conducted on composite-reinforced soil samples for verification of availability of the suggested method and the settlement estimation method of the reinforced GCP is proposed. Furthermore, for the verification of the proposed method, predicted settlements by the proposed method are compared with results of 3-dimensional numerical analyses. In addition, parametric studies are performed together with detailed analyses of relevant design parameters.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.39-49
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• 2007

In this study, quantitative sensitivity analysis on rockfill material influencing the dam crest settlement of CFRD (Concrete-Faced Rockfill Dam) subjected to earthquake loading was carried out. The purpose of this study is to indicate the most important input parameter from the results of sensitivity analysis, to show the quantitative variation of settlement at the crest of CFR type dam during earthquake with this input parameter, and to recommend the approximate estimation method of the settlement on the crest of CFRD subjected to earthquake loading. The statistic characteristics of rockfill parameters which were obtained from large triaxial tests were evaluated. The total 108 dynamic numerical analyses (2 input earthquake, 2 magnitudes for each earthquake, 27 rockfill material property combinations) on CFRD were conducted. The global sensitivity analysis was carried out using the results of numerical analysis. From the sensitivity analysis, It was found that the crest settlement of the CFRD subjected to earthquake was absolutely affected by the shear modulus of rockfill material irrespective of the input earthquakes and the magnitude of input acceleration. On the contrary, it was found that the effect of cohesion and friction angle of rockfill was negligible. From the results of sensitivity analysis and numerical analysis, the approximate estimation method of the settlement on the crest of CFRD subjected to earthquake loading was recommended on condition that the rockfill shear modulus and simple dam information was known.