• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1118-1125
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• 2005

In this study, seismic safety of CFRD(Concrete-Face Rockfill Dam) type "D" dam in operation is evaluated from the results of 1-g shaking table test using similitude laws. Model dam is made by similitude law considering the grain size of prototype dam component. After the model dam is impounded to the normal water level(N.W.L), it is excited by artificial earthquake wave corresponding to standard design respond spectrum of the "D" dam site. Displacement response behavior of the dam is examined through the measurement of vertical and horizontal displacement of dam crest. Also, amplification characteristics of acceleration with dam height is examined through the measurement of acceleration with dam height. Finally, the purpose of this study is to evaluate seismic safety of "D" dam in operation. From the results of acceleration measurement, it was found that acceleration of dam crest was amplified about 1.52 times compared to the acceleration of dam bottom and amplification phenomenon is outstanding at three quarters of dam height from the bottom of dam. From the analysis of displacement behavior, it was estimated that vertical displacement of prototype dam is 6.8cm (0.1% of dam height) and horizontal displacement 12.3cm(0.2% of dam height). These percentages is much lower than 1% of dam height(general stability criteria). Therefore, it was concluded that seismic stability of "D" dam against an estimated earthquake is guaranteed.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.57-64
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• 2005

Since the allowable bearing capacities of piles in weathered/fractured rock are mainly governed by settlement, the load-displacement behavior of the rock socketed pile should be well known. To predict pile head settlement at the design stage, the exact understanding of the load-transfer mechanisms is essential. Therefore, in this research, the load-transfer mechanisms of drilled shaft socketed into weathered rock was investigated. For that, 5 cast-in-place concrete piles with diameters of 1,000 mm were socketed into weathered gneiss. The static axial load tests and the load-transfer measurements were performed to examine the axial resistant behavior of the piles. A comprehensive field/laboratory testing program on weathered rock at the field test sites was also performed to describe the in situ rock mass conditions quantitatively. And then, the effect of rock mass condition on the load transfer mechanism was investigated. The side shear resistance of the pile in moderately weathered rock reached to yielding point at a few millimeter displacements, and after that, the rate of resistance increment dramatically decreased. However, that in the highly /completely weathered rock did not show the obvious yielding point, and gradually increased showing the hyperbolic pattern until with the relatively high displacement (>10 mm). The end bearing-displacement curves showed linear increase at least until with the base displacement of approximately 10 mm, regardless rock mass conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.706-713
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• 2004

This paper introduced an alternative method called USCP (Unpenetrated Sand Compaction Pile). In USCP, the toe of the sand pile does not reach to the lower supporting layer. Hence it is possible to reduce the amount of sand required. However, the degree of improvement could not be the same as SCP. Effective soil improvement, nevertheless, might be possible by combining both methods. In this paper, an improved method that cross over both SCP and USCP was discussed. And in order to verify applicability to a clay layer, consolidation behaviors with different conditions were analyzed and compared using FEM(Finite Element Method) based on the elasto-viscosity theory. From the results, it is concluded for the characteristic of settlement of USCP that the lower degree of replacement and the smaller ratio of penetration($H_d/H$), the larger is the settlement of the lower part of the clay layer comparing to the layer with no improvement. It is also concluded that the ratios of allotment of stress (m) calculated from the final settlements with 30% of degree of replacement are $1.8{\sim}3.3$ for $H_d/H=lOO%,\;1.8{\sim}4.0\;for\;H_d/H=75%,\;and\;1.8{\sim}3.8\;for\;H_d/H=50%$. Besides, the ratio of allotment of stress decreased as the degree of replacement decreased.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.249-257
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• 2006

The spatial distribution of design parameters greatly affects tunnel behavior during and after construction, as well as in the long-term temporal responses. However, the tunnel design parameters commonly used in numerical modeling tend to be representative or average values of global-scale properties. Furthermore, the uncertainty and spatial variation of the design parameters increase as the tunnel scale increases. Consequently, the probability of failure also increases. In order to achieve structural stability in large-section tunnels, the design framework must take into consideration the quantitative effect of design parameter variations on tunnel behavior. Therefore, this paper suggests a statistical approach to numerical modeling to explore the effect of spatially distributed design parameters in a circular tunnel. Also, the effect of spatial variation in the lining strength is studied in this paper. The numerical results suggest that the deformation around the tunnel increases with an increase in the variation of the design parameters.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.4
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• pp.441-455
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• 2015

In the present study, a face safety monitoring system was developed that will enable judging collapse risks on faces during tunnel construction to secure workers' safety. This system enables detecting abnormal behaviors of faces by analyzing the displacement of faces measured in real time using the x-MR control chart technique. In addition, an algorithm to judge false alarms was developed so that abnormal behaviors of faces and errors occurring in the process of work can be distinguished from each other by comparing the number of measured values exceeding the management criteria and moving range k. The results of the present study are applicable to real-time monitoring of behavior on the face in dangerous ground sections to minimize damage to workers.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.768-773
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• 2009

Measuring method being applied for off-shore works is performed by using data logger or manual measuring instrument with wiring the cable connected from the sensor up to the position where measuring is allowed.(upper part of embankment or marine structure) Measuring management by using existing measuring method may be acceptable on the condition that the ground deformation volume(vertical, horizontal) is generally minimal and the site condition is good. But loss of measuring instrument, sensor cable failure or cutting is taken place frequently due to significant change of ground behavior caused by an external force change(embankment, excavation) under very soft ground condition(N value below 0-4). In case of the marine works, in particular, loss rate of measuring instrument is highly represented due to the factors of working barge anchoring, constructional interference and natural disaster. In order to solve these problems, measuring management was performed with employing underground wireless system at the immersed tunnel site. Measuring data was obtained freely under the marine environment by using underground wireless communication and cable cutting potential by ground behavior could be reduced. Measuring cost savings and its installation convenience were maximized by way of off-shore tower installation or cabling and by minimizing constructional interference of off-shore working barge. This case of measuring management was accomplished successfully.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.63-72
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• 2013

The structural stability of fill dam largely depends on the engineering behavior of rock materials used as main zone for dam construction and it is necessary to understand well the stress-strain characteristics of fill materials as well as shear strength property. In addition, the numerical analysis of fill dam requires a thorough study for calibrating material properties and parameters of a coarse-grained soil constitutive model. In this paper, large triaxial test results for Buhang-dam fill materials are analyzed and constitutive model parameters are calibrated based on the test results. It is shown that MD constitutive model is capable to predict the stress-strain behavior of dense and loose coarse-grained soils used for Buhang-dam construction based on the comparison study between the experimental test result and numerical simulation.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.11-19
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• 2013

Coarse-grained soils are typical engineering materials commonly used in many civil engineering applications such as structural fills, subgrade and drainage fills for dam, railway and bridge. Various researches have been performed with related to constitutive laws for numerical analysis of such structures. This paper presents a parametric study for a constitutive model for coarse grained materials. The model is a kind of the bounding surface models based on critical state theory. A distinct feature of the model is to capture the response of coarse-grained materials with different void ratios and confining pressures using a single set of model parameters. The model behavior is defined with a set of elastic parameters, critical state parameters, and model-specific parameters. The parametric study was performed for the model-specific parameters. The result of parametric study shows that the model is capable to capture stress-dilatancy behavior and kinematic-hardening under non-associative plastic flow.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.387-398
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• 2018

The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.358-365
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• 2002

In this paper the model tests have been conducted and the results were compared with those by the theoretical methods to study the behaviors of the piled raft. The size of model box is 2.2m${\times}$2m${\times}$2m. The raft is made of rigid steel plate and piles are made of steel pipes. Generally the bearing capacity of group piles is designed with only the pile capacities, which is Ignored the bearing capacity of raft. But the uncertainty of pile-raft-soil interaction leads to conservative design ignoring the bearing effects of raft. In the case of considering the bearing capacity of raft, the simple sum of bearing capacity of raft and that of each pile cannot be the bearing capacity of piled raft. Because the pile-raft-soil interaction affects the behavior of piled raft. Thus the effects of pile-raft-soil interaction are very important in the optimal design. In this paper, the behaviors of piled raft are studied through model tests of 2${\times}$2, 2${\times}$3, and 3${\times}$3 pile groups. The spacing between piles is changed in the model tests. And the behaviors of free standing and piled raft are also studied.