• The Journal of Engineering Geology
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• v.24 no.1
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• pp.23-38
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• 2014

The composition of carbonate sands from a sabkha at Ruwais in the UAE differs from that of silica sand, and these sands are crushed easily under low compression pressures. Accordingly, particle crushing of carbonate sand occurs under high pressure, which results in additional settlement and reduces the shear strength. In this study, consolidation and triaxial tests were conducted to analyze the characteristics of carbonate sands following particle crushing. The unusual shear strength graphs of the carbonate sands result from the degree of particle pre-crushing. For the range at p' > p in the p (p')-q diagram, negative (-) excess porewater pressures occur if the axial pressure causes particle crushing that induces exposure of the inner voids. In addition, the q value decreased after particle crushing. In conclusion, the unusual characteristics of the carbonate sands were induced by particle crushing. The triaxial tests revealed that the degree of particle pre-crushing influenced the excess porewater pressure.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.9 no.1
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• pp.1-13
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• 2006

The recent environmental protection issue has diminished the supply of sand for soft ground improvements so much that the prices of sand have shown a sudden rise. Plastic material is one of substitutes for sand material, but plastic is nonperishable and doubtable if it has potential environmental hormone disrupting substances. Moderate-priced natural fiber drain board made with coconut coir and jute filter are in the spotlight recently as an alternative material for sand and plastic drain board etc. Natural fiber drain has not only competitive price but also a characteristic of assimilation into the soils after finishing of its own function. Discharge capacity of the fiber drain board evaluated by triaxial type discharge capacity test was relatively lower than that of plastic drain board. Nevertheless, settlement and pore pressure dissipation behaviors of the fiber drain board and the plastic drain board which were installed in the clayey soil during the composite discharge capacity test were almost similar. It was also found that biodegradation of the fiber drain board was in progress until 18 month after installation in the clayey soil, but they had still enough engineering properties to use at field.

• Journal of the Korean GEO-environmental Society
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• v.2 no.3
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• pp.57-69
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• 2001

Sand pile is widely used as a ground improvement method. Although the primary purpose of constructing sand pile is accelerating consolidation, composite ground effect also can be gained by constructing sand pile. This study was accomplished to understand composite ground effect on the ground improved by sand piles which were applied as vertical drainage material when area replacement ratio was small relatively. For determining bearing capacities of origin ground and sand piles and analysing interaction between embankment and origin ground, bearing tests and earth pressure monitoring are performed. From the results, it turned out that the contribution of sand pile as a load bearing mechanism is not substantial. However, the bearing capacity of sand pile was increased to sixty percentages when compared with origin ground. The increasement of bearing capacity could be caused the change of consolidation characteristics during the process of consolidation by overburden load. Therefore, the composite ground effects depending on stiffness increasement of sand pile would be estimated as a factor decreasing consolidation settlement.

• Journal of the Korean GEO-environmental Society
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• v.4 no.4
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• pp.17-23
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• 2003

Accurate prediction of consolidation behaviors of the soft ground improved by plastic board drains is not easy because the consolidation characteristics of the improved ground has not been fully elucidated yet. The shape of drains is one of the most important factors which affect the consolidation characteristics of the improved ground. In this paper, a series of model consolidation tests of soft clay ground improved by plastic board drain were carried out, in order to investigate the effect of both plastic board width and stress level on consolidation characteristics of the improved ground. As the results, behaviors of both settlement and excess pore pressure dissipation were elucidated. Also, the non-uniform distribution of water content in the model ground was obtained. Then, in order to investigate the effect of vertical drainage on the consolidation behavior in the model tests, the comparison between experimental consolidation behaviors and Barron's theoretical ones were carried out. As the results, it was elucidated that the consolidation behavior in the model tests was affected not only by radial drainage but also by vertical drainage.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.95-102
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• 1999

It is important to estimate the magnitude of settlement and the time of primary consolidation in geotechnical engineering projects. For these purposes, site explorations and laboratory tests are usually performed. However, the mechanical properties determined from laboratory tests on the samples obtained by different sampling techniques show different trends. In this study, three types of consolidation test were carried out on the soil samples obtained by three different sampling techniques (76mm tube, 76mm piston, and block samples), to verify the effect of sample disturbance on consolidation properties. It was found that sampling methods have influence on the $\varepsilon$ - log $\sigma$'$_{v}$ relationship. While insignificant difference of compression indices from the samples obtained by different sampling techniques was observed in compression region, these values showed a different trend in precompression region. The values of $c_{v}$ and k of block samples had a tendency to be larger than those of piston and tube samples. At consolidation pressure larger than $\sigma$'$_{p}$, however, these properties became similar regardless of sampling methods. The block and piston samples gave slightly higher values of $C_{a/}$ $C_{c}$ than tube samples. In the results of I $L_{EOP}$ and CRS test, it was observed that the values of $\sigma$'$_{p measured}$/$\sigma$'$_{p best estimated}$ of Yang-San clay decreases when strain becomes larger than 1.0% and that precompression strain of block samples is in the range of 1.5~2.0% while those of piston and tube samples are 1.75~3.75%. It was also shown that the values of $\sigma$'$_{p}$ of block samples exceed those of piston and tube samples by about 6~10%.6~10%.%.%.%.%.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.161-173
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• 1999

Settlement analysis based on oedometer test results with or without Skempton-Bjerrum's modification method ( widely used for practical purposes when estimating consolidation settlements of soft clay deposits) has shortcomings that it cannot simulate real stress states and deformation behaviors of soils in case that in-situ loading and deformation conditions are not 1-dimensional. In this study, the stress path method, reflecting various probable stress paths, was employed to normally - consolidated kaolinite samples by using automated triaxial testing device which can control stress paths automatically. From this experimental study, elastic, consolidation, secondary compression and pore pressure development - dissipation behaviors under various stress paths were analyzed and deformation characteristics of soft clays, which can be the basis of rational estimation of settlements, were studied. Also by comparing results of stress path tests with those of 1-dimensional consolidation tests, limitations and problems of conventional methods were clarified.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.42-48
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• 2006

This paper shows theresults of centrifuge model experiments to investigate the behavior of a replacement method in dredged and reclaimed ground. For this experimental work, centrifuge model tests were carried out to investigate the behavior of a replacement method in soft clay ground. Basic soil property tests were performed to find the mechanical properties of clay soil sampled from the southern coast of Korea, which was used for the ground material in the centrifuge model tests. The reconstituted clay ground of the model was prepared by applying reconsolidntion pressure in a 1 g condition with a specially built model container. Centrifuge model tests were carried out under the artificially accelerated gravitational level of 50 g. Replacement material of lead with a certain degree of angularity was used and placed until the settlement of the replacement material embankment reached a state of equilibrium. Vertical displacement of the replacement material was monitored during tests. The depth and shape of the replacement, especially the slope of the penetrated material and the water content of the clay ground were measured after finishing tests. Model tests for investigating the stability of an embankment after backfilling were also performed to simulate the behavior of a dike treated with replacement and backfilled with sandy material. As a result of the centrifuge model test, the behavior of the replacement, the mechanism of the replacement material being penetrated into clay ground, and the depth of the replacement were evaluated.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.507-534
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• 2015

The present work investigates the behavior of the embankment models resting on soft soil reinforced with ordinary and stone columns encased with geogrid. Model tests were performed with different spacing distances between stone columns and two lengths to diameter ratios (L/d) of the stone columns, in addition to different embankment heights. A total number of 42 model tests were carried out on a soil with undrianed shear strength $${\sim_\sim}10kPa$$. The models consist of stone columns embankment at s/d equal to 2.5, 3 and 4 with L/d ratio equal 5 and 8. Three embankment heights; 200 mm, 250 mm and 300 mm were tested for both tests of ordinary (OSC) and geogrid encased stone columns (ESC). Three earth pressure cells were used to measure directly the vertical effective stress on column at the top of the middle stone column under the center line of embankment and on the edge stone column for all models while the third cell was placed at the base of embankment between two columns to measure the vertical effective stress in soft soil directly. The performance of stone columns embankments relies upon the ability of the granular embankment material to arch over the 'gaps' between the stone columns spacing. The results showed that the ratio of the embankment height to the clear spacing between columns (h/s-d) is a key parameter. It is found that (h/s-d)<1.2 and 1.4 for OSC and ESC, respectively; (h is the embankment height, s is the spacing between columns and d is the diameter of stone columns), no effect of arching is pronounced, the settlement at the surface of the embankment is very large, and the stress acting on the subsoil is virtually unmodified from the nominal overburden stress. When $(h/s-d){\geq}2.2$ for OSC and ESC respectively, full arching will occur and minimum stress on subsoil between stone columns will act, so the range of critical embankment height will be 1.2 (h/sd) to 2.2 (h/s-d) for both OSC and ESC models.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.4
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• pp.345-356
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• 2004

Open-cut method has been widely used to construct underground structures, but it causes several problems such as traffic congestion and public resentment resulting from severe construction noise and ground settlement. In many cases, it is very difficult to build underground structures safely due to the unknown locations of buried facilities such as water pipes, drainage pipes, gas pipes and high-pressure cable conduits etc. Also in open-cut method, moving buried facilities causes additional cost and extension of construction period. Therefore, this paper is to present a case study in which Tubular Roof construction Method (T.R.c.M.), a newly developed construction method for underground structures using slab steel pipes and PC wall trench, is applied for the construction of a subway tunnel in Seoul. As a result, it is found that T.R.c.M. is a construction method by which tunnels can be constructed safely without any effect on the surrounding environment and traffic flow due to the minimized construction vibration and noise.

• Geotechnical Engineering
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• v.3 no.1
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• pp.7-24
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• 1987

Preloading surcharge method along with vertical drains was adopted to improve the performance of a very soft marine clay deposit. The onshore deposit, located in the Ulsan Bay area, consists of a 2 to 10m thick, very soft, highly compressible marine clay layer developed just below. the sea water level. The initial undrained shear strength of the clay layer was about 0.6 ton/m2. But, the deposit was designed after treatment to support some auxiliary facilities for a new ilo refinery plant, requiring bearing capacities of 3.6 to 5.4 ton/m2 and maximum allowablee settlement of less than 7.5cm. A total of 35, 000 wick drains Ivas installed to expedite drainage during preloading, and surcharge loads of up to 5m above the original ground level were applied in a step-by-step loading sequence to prevent ground failure by excess surcharge loads. An extensive program of field instrumentation was implemented to monitor the behavior of the clay deposit. Measurers!ends included settlements, excess pore pressure and its dissipation, ground farmer level fluctuation, and lateral movement of the so(t clay layer under the preloads. This paper describes the design concepts, construction methods and control procedures used for improvement of the clay layer. It also presents the ground behavior measured during construction, rind comparisons with theoretical predictions.