• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.173-178
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• 1993

The most appropriate mixing ratio of fly ash to bottom ash obtained from compaction characteristics and CBR values is varying from 5:5 to 6:4. But these mixed ashes are frost-susceptible materials according to judging by the paticle-size distribution because of a lot of silty-size paticles. In this study, the frost-susceptibility of compacted coal ash with proper mixing ratio is examined experimentally for use of subgrade materials. And, the efforts have been made to find proper cement addition in making these mixed ashes frost-insusceptible. It was revealed that these mixed ashes are frost-susceptible, and 4% of cement content is required to be made frost-insusceptable. It was found that amount of frost heave of these mixed ashes decreases with the unconfined compressive strength, and increases with log k if the permeability coefficient k is as low as the water into the freezing front of these mixed ashes is restricted.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.638-645
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• 2010

This study introduces a reinforcement work case using Twin-Jet Method. The area is located behind the abutment of the bridges built on soft clay along the $\bigcirc\bigcirc$ Express Highway. Its foundation was constructed by installing EPS blocks on the original ground to reduce the embankment load under the highway. However, the ground deformation has continuously occurred due to the settlement of the foundation soft cohesive soils. The amounts of subsidences at the surface turned out to be 20~30.0mm, After the pavement patch work on April 23, 2009, a drastic subsidence occurred together with 10mm swell, For this reason, Twin-Jet grout column construction was applied by passing through the EPS banking blocks without closing traffic flows on the express highway. The outcomes of core sample tests after reinforcing the ground turned out to be TCR 92.5%, RQD 64.6% and unconfined compressive strength 2.3~8.6Mpa. The test results showed that the condition of the ground foundation had improved using Twin-Jet grouting in most layers of ground including the cobble and gravel layer.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.10a
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• pp.334-408
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• 2006

In Hong Kong, large-diameter (${\ge}600mm$) bored piles and large-section excavated rectangular barrettes are commonly used to support tall buildings to resist both vertical and horizontal loads. These piles and barrettes penetrate through and may found in saprolitic soils and decomposed rocks. Generally, the design of these large bored piles and barrettes involves considerable amount of uncertainty and design parameters must usually be verified by field tests. In this paper, over 50 full-scale load tests on large-diameter bored piles and over 15 large-section of rectangular barrettes in Hong Kong are reviewed and interpreted critically, in particular the degree of mobilisation of side shear resistance using a mobilization rating (MR) factor and a displacement index (DI) for floating bored piles and barrettes and rock-socketed piles, respectively. The author was heavily involved with many of these load tests. The diameter of the bored piles tested ranges from 0.6m to 1.8m and the depth varies from 12m to 75m. Sizes of barrettes critically reviewed include $2.2m{\times}0.6m,\;2.2m{\times}0.8m,\;2.8m{\times}0.8m\;and\;2.8m{\times}1.0m$ (on plan) and the depth varies from 36m and 63m. Based on these field tests, a new failure load criterion for large-diameter bored piles and barrettes is developed and proposed. The side shear resistance of the bored piles and barrettes is quantitatively analyzed with respect to local displacements, standard penetration tests, unconfined compressive strength (UCS) for rock sockets and using the effective stress principle. In addition, the effects of construction including post-grouting, construction time, side scraping and excavation tools on side shear resistance are investigated and reported.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.138-144
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• 2011

Mine closure does often accompany the flooding of mine galleries due to ceasing a pumping operation. When a mine gallery is flooded, rocks around the gallery are fully saturated and the gallery is subject to a water pressure. The uniaxial unconfined compressive strength of a rock depends on its water content and decreases as the water content increases. A water pressure may originate the crack growth of a rock or the discontinuity growth of rock mass. Although the water in a gallery will give some support pressure inside the gallery, the degradation of rock mass properties caused by a water pressure will reduce the stability of the gallery. In this study, 2-dimensional discontinuous and 3-dimensional continuous numerical analyses have been conducted to evaluate an effect that a reduction of rock mass properties around the gallery induced by a water pressure has on the stability of mine gallery. The numerical analyses show that a reduction of rock mass properties caused by a water pressure increases displacements of rock mass around mine gallery. 2-dimensional model is found to give larger values of displacement than 3-dimensional model.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.972-978
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• 2008

Quality Assurance of Deep Mixing to fulfill the requirements of geotechnical design cannot be achieved only by the process control During production conducted by the deep mixing contractor but it should involve relevant activities that are carried out prior to, during and after the construction by all the parties involved in a deep mixing project. The requirement is different for different application, and hence, QA/QC method/procedure and verification technique may be different for different application. In order to maintain the high quality of deep mixing work in the global market, it is necessary to conduct a research project, such as investigation of illustrations, the variety of existing QA/QC methods/procedures, the correlation between the outcomes of different QA/QC methods. In these reason, it has been held the international meeting to discuss them, in that kind of activities in 2009 it will be held Symposium. Also Collaborative study for QA/QC is on goin, and conduction by all participated members. The subject for collaborative study are, task 1 : investigation of laboratory tests procedures, task 2 : comparing of different laboratory tests procedures, task 3 : QA/QC method/procedures, task 4 : integrated Task1 ~task 3. The discussion of the results in all task will be held in the Symposium separately. In this paper, it was presented four tasks. Also the results in task 1 and 2 conducting domestically until now, such as investigation of laboratory test procedures, effect on the unconfined compressive strength by aging temperature and by delayed time.

• Journal of Environmental Health Sciences
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• v.19 no.2
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• pp.46-54
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• 1993

This study was carried out on the stabilized/solidified treatment for the reducing leachability of hazardous heavy metals copper, lead, chromium and cadmium in the hazardous sludge which treated to be unleached heavy metals by sodium diethyl dithiocarbamate. Cement matrix was analyzed for the leachability of 24 hrs and dynamic leaching test, structure and the optimum condition for the stabilization and solidification of the hazardous sludge. In 28 days of curing time the unconfined compressive strength was 21.5 kg/cm$^2$ at the ratio of portland cement (0.5)+fly ash (0.25) and 23.5 kg/cmz at the ratio of portland cement (0.5)+fly ash (0.25) + cake (0.25). High concentration of Pb, Cr and Cd in the sea water and Cu in the distilled water were leached at the dynamic leaching test. The concentration of leaching heavy metals for specimens which were tested 24 hrs were found low leachability with decreasing pH of leachant. According to dynamic leaching test, the low level of copper, lead, cadmium and chromium were leached in the cement matrix with sodium diethyl dithiocarbamate. But the effective diffusion coefficient of unleached cement matrix which was treated sodium diethyl dithiocarbamate was decreased above 2 times than that of cement matrix. The relation of leachant renewal period (Y) and cumulative fraction ion leached (X) was the following regression equations. Solidification with unleached agent. Y$_{Cu}$ = 1413752X + 247, Y$_{Pb}$ = 223501IX + 214, Y$_{Cr}$ = 8310601X - 472, Y$_{Cd}$ = 168787X + 1061 The structure of' solidified matrix with X-ray diffraction analysis was composed more Ca(OH)$_2$, Si, Mg(OH)$_2$ and Al in the unleached cement matrix than those in cement matrix.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.323-334
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• 2003

For performance-based design using nonlinear static analysis, it is required to predict the inelastic behavior of structural members accurately. In the present study, a nonlinear numerical analysis was peformed to develop the method describing the moment-curvature relationship of structural wall with boundary confinement. Through the numerical analysis, variations of behavioral characteristics and failure mechanism with the arrangement of vertical reinforcement and the length of boundary confinement were studied. According to the analysis, the maximum moment-carrying capacity of structural walls with adequately confined boundary elements is developed at the moment the unconfined concrete reaches the ultimate compressive strain. Walls with flexural re-bars concentrated on the boundaries fails in a brittle manner. As vortical re-bars in the web increases, the brittle failure is prevented and a ductile failure occurs. Based on the findings, moment-curvature curves for walls with a variety of re-bar arrangement were developed. According to the proposed relationships, deformability of the structural walls wth boundary confinement increases as the compressive strength of the confined concrete increases compared to the applied compressive force.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6C
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• pp.241-250
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• 2011

The design method of IGM proposed by FHWA to predict bearing capacities of drilled shaft socketed in weathered granite has been used generally. In this study, site investigations were performed in a pilot test site, and disturbance and roughness were measured. Geotechnical properties were assorted as cohesive material and undisturbed and smooth surface. A simple relationship was proposed to predict unconfined strength ($q_u$) of weathered granite using static load test results, load transfer test results and N values. It was confirmed that the design method to estimate bearing capacities of drilled shaft could improve IGM's theory for weathered granite from this research.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.43-52
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• 2007

There is a growing range of applications for concrete-filled steel tube (CFT) member because of its superior performance. But a CFT member may be uneconomical or has weight problems because it is fully filled with concrete. In this study, a new type of member, called internally confined hollow (ICH) CFT member, was developed to solve the high cost and weight problems of the CFT member. To determine stress-strain model of the concrete in an ICH CFT column, possible failure modes of an ICH CFT column were suggested and confining pressure was derived from equilibriums for each failure mode. From the derived equations, a computer program was coded and parametric studies were performed for some examples. Analytical results showed that internally confined concrete has enhanced strength and ductility compared with those of unconfined or biaxially confined concrete.

• Journal of the Korean GEO-environmental Society
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• v.15 no.3
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• pp.5-13
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• 2014

This paper presents the results of a numerical investigation on applicability of Light-weighted Foam Soils (LWFS) consisted of dredged soils for soft ground improvement. The engineering properties of LWFS were comprehensively investigated based on the previous experimental tests. And three dimensional numerical models which reflect soft ground conditions were adopted to evaluate the applicability of LWFS compared to SCP and DCM. A number of cases were analyzed using a stress-pore pressure coupled model. The results indicated that LWFS method enables to reduce more settlement, lateral flow and heaving than SCP method and enable to reduce more residual settlement than DCM method. Also it was revealed that such effect depends on the properties of LWFS such as unit weight, unconfined compressive strength, deformation modulus and Poisson's ratio.