• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.379-386
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• 2001

Piled raft foundations are usually used to reduce total and differential settlements of superstructures. In the piled raft foundations, the raft is often on its own able to provide adequate bearing capacity and only few widely spaced piles are added to the foundation to keep settlements be1ow a certain limit. In this paper, experimental studies on the load sharing ratio between piles and raft are carried out. Also, for evaluating the application of optimum design technique using a genetic algorithm, optimal locations of files are compared with the results of laboratory model tests. from tile results of laboratory model tests, there are found that the load sharing ratio between files and raft is depended on the number of piles and stiffness of raft, and the optimal locations of piles became concentrated on the middle of rafts. From these results of laboratory model tests, the optimum technique using a genetic algorithm is acknowledged to the application in the piled raft.

• Journal of the Korean Society of Safety
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• v.12 no.3
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• pp.147-154
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• 1997

The main purpose of this study is to investigate the failure surface in a soil mass by a excavation of the model ground. The failure mechanism of an earth structure is usually determined from field failure observations or from laboratory model tests at failure. To study the failure surface for the excavated slope, laboratory model tests were performed by changing the angle of the excavated slope and the ground condition. Results of the laboratory model tests were compared with those obtained with theoretical solutions using limit equilibrium analysis method. The results of model tests show that, there is a failure to create a straight line in the low angle of excavated surface and a create a circle as the angle increases. As the angle of excavated surface is increasing, the angle of the failure surface increases too. In the angle of the failure surface, the submerged ground is less than the dry ground at $3.2^{\circ}$.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.21-27
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• 2019

Rockburst disasters pose serious threat to mining safety and underground excavation, especially in China, resulting in massive life-wealth loss and even compulsive closed-down of some coal mines. To investigate the mechanism of rockbursts that occur under a state of static forces, a stress model with sidewall as prototype was developed and verified by a group of laboratory experiments and numerical simulations. In this model, roadway sidewall was simplified as a square plate with axial compression and end (horizontal) restraints. The stress field was solved via the Airy stress function. To track the "closeness degree" of the stress state approaching the yield limit, an unbalanced force F was defined based on the Mohr-Coulomb yield criterion. The distribution of the unbalanced force in the plane model indicated that only the friction angle above a critical value could cause the first failure on the coal in the deeper of the sidewall, inducing the occurrence of rockbursts. The laboratory tests reproduced the rockburst process, which was similar to the prediction from the theoretical model, numerical simulation and some disaster scenes.

• Tunnel and Underground Space
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• v.21 no.3
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• pp.216-224
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• 2011

In this study, Class II behavior of rock failure process under uniaxial and biaxial compression has been numerically simulated using bonded particle model. Class II behavior of rock was simulated by radial strain controlled uniaxial and biaxial compression tests using a suggested method of ISRM. Micro-parameters used in the simulation were determined based on the laboratory uniaxial compression tests carried out at ${\"{A}}sp{\"{o}}$ Hard Rock Laboratory, Sweden. Class II behavior of ${\"{A}}sp{\"{o}}$ rock was effectively simulated using newly proposed numerical technique in this study, and the results of numerical simulations show good similarity with the complete stress-strain curves for Class II behavior obtained from the laboratory tests.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.691-711
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• 2016

In this study, the uplift capacity of anchor plates embedded in sand was investigated by conducting model tests. Square shaped anchors were used in the tests and parameters such as relative density of sand, embedment ratio (H/B), spacing ratio between anchors (S/B) and anchor configuration affecting the uplift capacity were investigated. Breakout factor and group efficiency which are dimensionless parameters were used to show the results. A series of finite element analyses and analytical solutions were additionally performed to ascertain the validity of the findings from the laboratory model tests and to supplement the results of the model tests. It can be concluded that the embedment depth in dense sand soil condition is the most important parameter with respect to the other parameters as to influencing the uplift capacity of group anchors.

• Journal of Applied Reliability
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• v.7 no.3
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• pp.127-136
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• 2007

The accelerated life tests(ALTs) and degradation characteristics of image intensifier assembly(KIT-7) under low illuminance and high temperature were investigated. The accelerated life tests were carried out at $5{\times}10^5\;fc-40^{\circ}C,\;10{\times}10^5\;fc-40^{\circ}C,\;5{\times}10^5\;fc-50^{\circ}C,\;10{\times}10^5\;fc-50^{\circ}C$ and relationship related to illuminance and temperature was used as an accelerated life test model. An ALTA program[6] was used to calculate an acceleration factor and the test of life distribution fit, and estimate three parameters of an life test model. To sum up, MTTF 10,000 h at $5{\times}10^{-5}\;fc-40^{\circ}C$ of image intensifier assembly was certificated.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.348-351
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• 2005

In this study, solute breakthrough curves through the unsaturated zone were predicted using artificial neural network (ANN) by numerical tests and laboratory experiments. In the numerical tests, applicability of ANN model to prediction of breakthrough curves was evaluated using synthetic data generated by HYDRUS-2D. An appropriate strategy of ANN application and input data form were recommended. The ANN model was validated by laboratory experiments comparing with HYDRUS-2D simulations. The results show that the ANN model can be an effective method for forecasting solute breakthrough curves through the unsaturated zone when hydraulic data are available.

• Journal of the Korean Geosynthetics Society
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• v.21 no.1
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• pp.33-48
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• 2022

This paper presents illustrative examples of the application of advanced digital image correlation (DIC) technology in the geotechnical laboratory tests, such as shallow footing test, trapdoor test, retaining wall test, and wide width tensile test on geogrid. The theoretical background of the DIC technique is first introduced together with fundamental equations. Relevant reduced-scale model tests were then performed using standard sand while applying the DIC technique to capture the movement of target materials during tests. A number of different approaches were tried to obtain optimized images that allow efficient tracking of material speckles based on the DIC technique. In order to increase the trackability of soil particles, a mix of dyed and regular sand was used during the model tests while specially devised painted speckles were applied to the geogrid. A series of images taken during tests were automatically processed and analyzed using software named VIC-2D that automatically generates displacements and strains. The soil deformation field and associated failure patterns obtained from the DIC technique for each test were found to compare fairly well with the theoretical ones. Also shown is that the DIC technique can also general strains appropriate to the wide width tensile test on geogrid, It is demonstrated in this study that the advanced DIC technique can be effectively used in monitoring the deformation and strain field during a reduced-scale geotechnical model laboratory test.

• Proceedings of the Korean Geotechical Society Conference
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• 1998.10a
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• pp.305-312
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• 1998

• Wind and Structures
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• v.20 no.2
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• pp.349-361
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• 2015

Higher-mode vertical vortex-induced vibrations (VIV) have been observed on several steel box-girder suspension bridges where different vertical modes are selectively excited in turn with wind velocity in accordance with the Strouhal law. Understanding the relationship of VIV amplitudes for different modes of vibration is very important for wind-resistant design of long-span box-girder suspension bridges. In this study, the basic rectangular cross-section with side ratio of B/D=6 is used to investigate the effect of different modes on VIV amplitudes by section model tests. The section model is flexibly mounted in wind tunnel with a variety of spring constants for simulating different modes of vibration and the non-dimensional vertical amplitudes are determined as a function of reduced velocity U/fD. Two 'lock-in' ranges are observed at the same onset reduced velocities of approximately 4.8 and 9.4 for all cases. The second 'lock-in' range, which is induced by the conventional vortex shedding, consistently gives larger responses than the first one and the Sc-normalized maximum non-dimensional responses are almost the same for different spring constants. The first 'lock-in' range where the vibration frequency is approximately two times the vortex shedding frequency is probably a result of super-harmonic resonance or the "frequency demultiplication". The main conclusion drawn from the section model study, central to the higher-mode VIV of suspension bridges, is that the VIV amplitude for different modes is the same provided that the Sc number for these modes is identical.