• Journal of the Korean GEO-environmental Society
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• v.6 no.4
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• pp.59-64
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• 2005

Although high pressure discharge method is widely used for improving soft ground, it has various problems including lack of strength increase and the possibility of water pollution and soil contamination. MJM(Morta Jet Method) uses sand in addition to cement as the injection material. MJM uses triple rods with a built-in nozzle that allows easier discharge of the slime, resulting in higher replacement area ratio and more uniform formation of pillar hydrates, and thus results in significant increase in strength. MJM is expected to perform especially well as piles in marine clays. This study investigates the field applicability of the MJM through extensive laboratory and field tests.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.59-69
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• 2019

Grout injection is mainly used for permeability reduction and/or improvement of the ground by injecting grout material into pores, cracks, and joints in the ground. The oscillatory grout injection method was developed to enhance the grout penetration. In order to verify the level of enhancement of the grout, field grout injection tests, both static and oscillatory tests, were performed at three job sites. The enhancement in the permeability reduction and ground improvement effect was verified by performing a core boring, borehole image processing analysis, phenolphthalein test, scanning electron microscopy analysis, variable heat test, Lugeon test, standard penetration test, and an elastic wave test. The oscillatory grout injection increased the joint filling rate by 80% more and decreased the permeability coefficient by 33-68%, more compared to the static grout injection method. The constrained modulus of the jointed rock mass was increased by 50% more with oscillatory grout injection compared to the static grout injection, indicating that the oscillatory injection was more effective in enhancing the stiffness of the rock mass.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.77-89
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel that allows tunnel segments to float underwater by buoyancy, and is being actively studied in recent years. When the submerged floating tunnel is connected to the ground, the tunnel and the bored tunnel inside the ground must be connected. There is risk that the stress will be concentrated at the connection between the two tunnels due to the different constraints and behavior of the two tunnels. Therefore, special design and construction methods should be applied to ensure the stability around the connection. However, previous studies on the stability at the connection site have not been sufficiently carried out, so study on the basic stage of the stability at connection site are necessary. In this study, numerical analysis simulating the connection between submerged floating tunnel and the bored tunnel confirmed that the shear strain concentration occurred in the ground around the connection, and it was analyzed that the structural factors can be handled during construction to have effects on the stability of the ground around the connection. Numerical results show that the risks from disproportionate displacements in the two tunnels can be mitigated through the construction of grouting material and joint design. Although the results from this study are qualitative results, it is expected that it will contribute to the determination of structural factors and risk areas that should be considered in the design of connections between the submerged floating tunnel and bored tunnel in the future studies.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.653-657
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• 2005

This study applied the NDS method to the creek levee and the foundation of a building, for the purpose of ground improvement and cut-off. The conclusions are shown in the following. (1) The results of the field tests in the creek levee are as follows; the N value of the standard penetration test is $2{\sim}3$ before NDS grout and $9{\sim}21$ after NDS grout; in the alluvial layer, $7{\sim}11$ before NDS grout and $14{\sim}23$ after NDS grout. This confirms increasing ground strength with consistency ranging from stiff to very stiff. (2) The result of the permeability test in the creek levee shows that the ground had a great hydraulic conductivity with complete leakage before ground improvement but that the hydraulic conductivity has significantly increased to $3.17{\times}10^{-5}{\sim}4.65{\times}10^{-5}cm/sec$ after ground improvement by the NDS method. (3) The result from the field test of the foundation of the building confirms great reinforcing effects, showing that the allowable bearing capacity has increased from Pa = 5.0 $t/m^2$ before reinforcement to Pa = 25.0 $t/m^2$ after reinforcement.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1838-1844
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• 2007

The Wonhyo Tunnel on KTX railroad line is a section of latest concerns from domestic environmental NGOs, which focus on potential destruction of ecosystem or the like due to ever-depleted swamp water at about 300m upward from the tunnel under construction. As a result of study, out of all swamps in the vicinity of the tunnel, it was found that Mujechi 1st and 2nd swamps have been getting smaller in their area little by little since 50 years ago primarily under the influence of eroded streams around lower swamp and even ever-increasing annual mean temperature. As the result of monitoring about swamp before work, it was found that swamp water depends absolutely on amount of rainfall. Besides, the results of monitoring during work also didn't show any leakage generated in the tunnel during and after excavation works with regard to a wheat field swamp in the most vicinity of the tunnel (80m away). On the other hand, it was found that the range affected by ground water sink in tunnel section without grouting process amounted to about 100m around the tunnel, which indicates that such ground water sink has no significant impact upon most of swamps near the tunnel. As the result of testing by two well tracer test around swamps, it was noted that swamp water didn't run out from the bottom of swamp even with adjacent ground water level sunk in factitious ways. And the results of physical survey showed that swamp kept saturated even in dry season when ground water level becomes lower than the bottom of swamp. Therefore, even supposing that ground water level becomes sunk due to tunnel works, it is estimated that the water level of swamps would be still kept owing to impervious layer(peat beds).

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.49-83
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• 2005

ESCP Project showed an urban excavation case and introduced design method for case of Soil-Structure behavior in urban excavation. In this case, a retaining structures design to analysis the behavior of retaining wall and adjacent structures in urban excavations was applied by using a Elasto-plastic beam and limit Equilibrium analysis and soil-structure interaction analysis. Reliable design of earth retaining structures and the ground adjacent to braced wall in urban excavation are often difficult due to many variable factors. The ground settlement and the damage of adjacent structures in urban excavation has been an imprtant issue. Therefore, the stability of the adjacent structures must be secured with the excavation support and research on the protection of adjacent structure is necessary.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.2 s.13
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• pp.13-18
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• 2004

In this study, in the first place, parameters primarily influencing displacement and stress were constructed by using the Finite Difference Method; then using those parameters, the result of crown displacement and convergence among the existing, experimental values of a centrifuge model were compared with the result of numerical analysis; and then considering the stress and time effect of lining installation, parameters according to the difference of stiffness were studied. In the result of this study, it found out that rough, ground reinforcement effect manifests itself when reinforcement propert of the grouting of the big scale steel pipe through 3-D analysis is E= 4,000tf/m2 which of the stiffness of the original ground.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1473-1478
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• 2010

For the cassion type of breakwater under the condition of large wave loads, stability about lateral movement of breakwater was investigated by performing centrifuge model experiments. Prototype of breakwater was modelled by scaling down to centrifuge model and the soft ground reinforced with grouting was also reconstructed in the centrifuge model experiments. Sandy ground beneath breakwater was prepared with a soil sampled in field so that identical value of internal friction angle could be obtained. Centrifuge model experiments were carried out to reconstruct the construction sequence in field. Lateral static wave load was applied to the model caisson after the final stage of construction sequence was rebuilt and the measured lateral movement of caisson was compared with allowable value by the code to assess the stability about lateral movement of the breakwater.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.405-410
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• 2009

This paper presents a case study that achieved both of serviceability and safety of the building through soil reinforcement and restoration around foundations subjected to serious differential settlement using D-ROG method. The building which has one basement floor and three ground floors is founded on soft ground and differential settlement occurred to the maximum extent of 678mm. The foundation type of the building is a independent mat foundation. Soil profiles consist of landfill layer, alluvial layer, weathered rock, and soft rock. The bearing layer consisting of gravel and weathered rock is located 16.0~17.0m below the bottom of the building. As a result of soil reinforcement and restoration, the recovery ratio of more than 90% can be attained with the maximum set-up of 657mm.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.571-578
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• 2009

Recently, micropiling techniques are increasingly applied in foundation rehabilitation/underpinning and seismic retrofitting projects where working space provides the limited access for conventional piling methods. Micropiling techniques provide environmental-friendly methods for minimizing disturbance to adjacent structures, ground, and the environment. Its installation is possible in restrictive area and general ground conditions. The cardinal features that the installation procedures cause minimal vibration and noise and require very low ceiling height make the micropiling methods to be commonly used for underpin existing structures. In the design point of view, the current practice obligates the bearing capacity of micropile to be obtained from skin friction of only rock-socketing area, in which it implies the frictional resistance of upper soil layer is ignored in the design process. In this paper, a new micropiling method and its verification studies via field installation are presented. The new method provides a specific way to grout bore-hole to increase frictional resistance between surrounding soil and pile-structure and it allows to consider the skin friction of micropiles for upper soil layer during design process.