• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.43-50
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• 2005

Jet grouting method is widely being used in many geotechnical problems, especially for the purpose of reinforcement of clayey ground and cut-off wall of sandy ground. However, its design depends on highly empirical method, in which many researches have been undertaken. This study investigated the effect of cavitation on jet grouting. Small-scaled model tests were carried out using specially designed and fabricated device to analyze the effect of cavitation on jet grouting with various test conditions including ground condition, injection pressure, and injection time. The test results show that cavitation has a significant effect on jet grouting, and it has a potential for engineering application.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4D
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• pp.377-386
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• 2010

This study was conducted to find out the characteristics of the expanded road embankment constructed by the lightweight air-mixed soil (slurry density $10kN/m^3$) for a short-term without any ground improvement. Compression strength, capillary rise height of the lightweight air-mixed soil and settlement behavior of soft ground were studied. Compression strengths of the specimens sampled at the site after 1 and 5 months of construction were all satisfied the required strength 500 kPa. However, it was not convinced the homogeneity construction, because the values of strength were depending on the sampled location. Also, strength difference between laboratory and site specimens were found about 19%, and thus it should be considered for mixing design. Capillary rise reached about 20 cm for 70 hours because of a numerous tiny pores existed inside the lightweight air-mixed soil. Relationship between settlement and time of the soft ground placed underneath the expanded embankment was estimated by using the measured data and back analysis technique. The current average consolidation ratio and the final settlement after 120 months later were estimated about 32% and 4.5cm, respectively. This settlement is much less value than the allowable settlement 10cm for this structure.

• Journal of the Korean GEO-environmental Society
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• v.8 no.5
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• pp.39-46
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• 2007

In this study, the centrifuge tests were performed to investigate the lateral flow behavior and stability of the ground improved by SCP. The centrifuge tests were fulfilled in the case of the back of abutment filled by EPS (case 1) and soil (case 2), and the potentiometer was installed on the abutment and embankment to measure the vertical and horizontal displacement at the top of abutment. As a result, the vertical displacement measured at the back of abutment was maximum 2.1 m, which was about 12% if compared with the height of embankment. In the case of the back of abutment filled by soil, the vertical and horizontal displacement measured at the top of abutment was 10 cm and 1.1 m, respectively, which exceeded the allowable horizontal displacement. On the other hand, in the case of the back of abutment filled by EPS, the vertical displacement of abutment did nor occur and the horizontal displacement was 1.4 cm. Therefore, the effect of SCP improvement with EPS method adopted to prevent the lateral flow and assure the stability of embankment on the soft ground was far superior.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11c
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• pp.143-155
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• 1999

An experimental study has been carried out to investigate the reinforcing effect of marine dredging clay(MDC) mixed with the Micro-Fiber(MF). A series of laboratory tests was performed using specimens of MDC alone and MDC with MF by means of uniaxial and triaxial compression test. In the test programme, three stages of water content of MDC were chosen according to the elapsed time after dredging, and content and length of MF were considered as important factors for reinforcing effect. And the developed strength due to curing was measured both in MDC and composite. The enhancement of strength of composite was found to be increased with the increasing content and length of MF, and curing time, and with decreasing water content of MDC. An additional study has been made for in-situ trafficability on the soft reclaimed ground by MDC due to high water content. It was found that the waste lime was to be applicable for this purpose to get a reinforcing effect of MDC. A further study would lead to the better understanding of the reinforcing mechanism of the composite.

• Proceedings of the Korean Geotechical Society Conference
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• 1992.10a
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• pp.113-120
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• 1992

The construction of container terminal at Brani, Singapore required the improvement of soft clay layer having the thickness of about 6.5m, average moisture content of 79.4%, liquid limit of 90.4%, plastic limit of 21.8%, field vane strength of 10 to 25 KPa, pre-consolidation pressure of 225 to 60 KPa and compression index of 0.4 to 1.0. For the improvement of this layer, Colbon drains of 1.3m spacing in triangular pattern were installed to the bottom of the layer and surcharge of more than 11.25m high sand fill was later applied to the treated area. The settlement and lateral displacement of the ground were measured and the speed of surcharge filling was controlled, based on these readings. The removal of surcharge was determinied using the estimated time for the 90% degree of consolidation under the design pressure of 180KPa. The field and laboratory test results show that the soft clay layer has been improved substantially in its strength and consolidation characteristics: increase in strength of about 50KPa and pre-consolidation pressure and decrease in void ratio and compression index.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.133-142
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• 2006

Pusan clay, which is distributed in the Nakdong River estuary, is unusually soft and thick compared with other clays in the world. Because the consolidation settlement of the clay was significantly underestimated in several recent reclamation projects, it has been emphasized particularly on the need of studying the permeability characteristics. This study carries out vertical and horizontal permeability tests on undisturbed and consolidated samples from two sites of the area. The results of the study show the peculiar permeability anisotropy and the relationships with other indexes on Pusan clay and also comparison with those of other world clays.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.33-43
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• 2002

Recently, as large constructions on the coast increase, an application of a surface layer stabilization method which is one of the improvement methods for dredged soft clay has increased. However, there are few studies about this. The purpose of this study is clarifying characteristics of ultra-soft marine clay and hardening agent. Also, it is verifying an optimal mixture ratio of hardening agent through the laboratory tests according to designed experiments and proving by statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil in accordance with the design of experiments. Regression equations between hardening agents materials and unconfined compressive strength were derived from the tests. The applicability of regression equations were also verified by pilot tests. From the test results, it was found that hardening agent materials(cement, slag, fly-ash, inorganic salts, arwin, gypsum etc.) have some effect upon compressive strength. The optimal mixture ratio which satisfies the required compressive strength was derived from the statistical analysis. The effect of ground improvement by cements and hardening agents was confirmed through the pilot tests. This study will suggest data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.57-64
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• 2007

This study proposes a method to estimate drilling torque during ground boring with an aid of electrical energy required for rotating a boring-auger. Ground boring is commonly used in geotechnical engineering such as preboring precast pile installation, soil-cement grouting, ground exploration and so forth. In order to understand the correlation between required electrical energy to rotate the boring auger and the drilling torque, a small laboratory apparatus was designed and a pilot study was performed. The apparatus rotates common drill bits of $D=5{\sim}25mm$ in CBR specimens. The velocity of a bit is 19 RPM and predefined using a reduction gear which connects a main rotation axis to a 25 Watts AC electrical motor shaft. In the middle of drilling the motor current increments and the drilling torque were measured and the correlation between the current and the torque was obtained through linear square fits. Based on the correlation the acquired motor current during drilling was applied to predict the drilling torque in consequent testing and the prediction results were compared to the measured torque. The comparison leads a conclusion that the motor current during drilling using electrical power may be a good indicator to estimate/determine strength characteristics of the ground.

• Journal of the Korean Geosynthetics Society
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• v.11 no.2
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• pp.11-20
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• 2012

Partially penetrated SCP method is to install sand compaction piles in a soft clay layer not penetrating to the bed layer. In this study, consolidation behaviors of soft grounds improved by both partially and fully penetrated SCP methods are presented. When the replacement ratio is low, the settlement characteristic of the ground improved by fully penetrated SCP method seems to be consistent regardless the degree of consolidation. On the other hands, the ground improved by partially penetrated SCP method appears to decrease depending on the degree of consolidation. In addition, the settlement of upper clay layer is more increasing as the penetration ratio ($H_d/H$) is decreasing. No effect of stress concentration at the lower part of the partially penetrated SCP method is developed. The ratio of stress sharing appears to be almost consistent regardless the degree of consolidation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.3
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• pp.197-205
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• 2004

The relationships were studied between the range of hardening zone and the intensity of vacuum pressure in case of applying vacuum consolidation drainage method for soil improvement. A testing apparatus was made to measure the range of hardening zone varying the water content and the intensity of vacuum pressure for 3 different the highly compressible dredged clays(Gwangyang, Busan and Mokpo). In case of applying high vacuum pressure, the hardening zone is not spreaded as compared to low vacuum pressure because of the clogging of drainage and developed hardening zone near the drainage.