• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.09a
• /
• pp.829-834
• /
• 2009

Alluvial soil is one of the most difficult grounds for tunneling works due to the insufficient ground strength and excessive ground water inflow. Dduk island in Seoul has a wide alluvium developed by two rivers, Han and Jung-Ryang. Subway tunnel of $\bigcirc\bigcirc$ line planed across Dduk island has highly poor ground conditions due to small cover and deeply developed alluvium. Moreover, much part of this tunnel is located parallel to the bridge foundations of another railway with a small horizontal distance. Original design was done in 2002 and construction has been in progress. During the construction, tunnel design has been partly changed and adjusted for the complex ground condition and the demand from related organizations. This paper intend to introduce the urban tunnel design and construction in alluvial soils. This line could be divided three sections(A, B, C) according to ground and adjacent conditions. Section A is featured by mixed tunnel faces consisted with alluvial soils and weathered or weak rocks. The feature of section B is that tunnel underpasses near the bridge foundations of another subway. Lastly, section C with a very short length is the most difficult construction conditions due to the small cover, poor ground, obstacles on and underneath ground surface.

• Magazine of korean Tunnelling and Underground Space Association
• /
• v.1 no.2
• /
• pp.59-71
• /
• 1999

Recently, many deformations in tunnel such as crack and leakage were occulted. Specially, the defects of tunnel lining have been a serious problem in safety and stability many repair works for maintenance in tunnel have been carried out. Therefore, it is necessary to estimate the structural cracking for countermeasure in deformed tunnel and to investigate on the characteristics of lining system and the soundness of tunnel. In this study model tests for tunnel lining were carried out using test apparatus and centrifuge, In the direct loading test, the prototype was Kyungbu high-speed railway tunnel and the scale is 1/10, and lining models were made of concrete. Test conditions included load conditions such as direction, shape and type, lining conditions such as single and double lining, thickness, and reinforcement. In centrifuge model test, the prototype was Seoul subway tunnel and the scale is 1/100, and lining models were made of aluminum and hydrostone. Test conditions included tunnel defects such as thickness shortage. behind cavity and longitudinal cracks, reinforcement methods such as epoxy, grouting and carbon sheet. From these model tests , the characteristics of deformation and failure for tunnel lining were estimated, and the structural behaviors of deformed lining and the effects of repair and reinforcement for tunnel lining were researched.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.6
• /
• pp.905-913
• /
• 2017

To design segment lining, loads such as self weight, vertical load, horizontal load, ground reaction, water pressure, backfill grouting pressure et al. have to be considered. Earth pressure and water pressure are the major factor to design segment lining such as concrete strength, segment thickness and amount of rebar et al. To analysis earth pressure and water pressure acting on segment lining, filed monitoring and back analysis are performed in this study.

• Geomechanics and Engineering
• /
• v.21 no.2
• /
• pp.133-142
• /
• 2020

Submerged floating tunnel (SFT) is a type of tunnel which causes the tunnel segments to float in the water. When the SFTs are connected to the ground, the connection between the SFT and the subsea bored tunnel is fragile due to the difference in behavioral characteristics between the two types of tunnels. Therefore, special design and construction methods are needed to ensure the stability of the area around the connection. However, since previous research on the stability of the connection site has not been undertaken enough, the basic step necessitates the evaluation of ground behavior at the shore connection. In this study, the numerical analysis targeting the shore connection between the subsea bored tunnel and the SFT was simulated. The strain concentration at the shore connection was analyzed by numerical simulation and the effects of several factors were examined. The results showed the instability in the ground close to the shore connection due to the imbalance in the behavior of the two types of tunnels; the location of the strain concentration varies with different environmental and structural conditions. It is expected that the results from this study can be utilized in future studies to determine weak points in the shore connection between the submerged floating tunnel and the subsea bored tunnel, and devise methods to mitigate the risks.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09c
• /
• pp.11-17
• /
• 2010

Numerical analysis was carried out in order to simulate the development of the large deformation that took place on the reinforced earth wall, a part of the Tottori expressway planned to pass Hyogo, Japan. Since this reinforced earth wall had experienced unexpected deformation of the wall during construction, the wall was re-constructed twice. However, the wall deformation showed no sign to cease even at the final stage of the construction. Countermeasures to re-stabilize the wall were demanded. In part I of this paper, it was manifested that subsidence of a 3-meter weak soil due to seepage flow was responsible for the large deformation. A part of concrete panel wall was severely damaged due to extremely large pulling force of geotextile induced by the hammock state. As for the countermeasures, "grouting with slag system" was applied to fill voids of the backfill, and also to prevent further development of settlement in the weak soil layer. "Ground anchor" was also considered to achieve the prescribed factor of safety.

• The Journal of Engineering Geology
• /
• v.11 no.2
• /
• pp.141-152
• /
• 2001

The waterway tunnel zone (length 1,484m) in the Hyeonseo-myeon area that is a part of Yeongcheon dam waterway tunnel has been studied to characterize the relationship between groundwater inflow into the waterway tunnel and hydrogeologic characteristics. The effects of sandstone thickness in the tunnel section. fracture density, fracture aperture and spacing, fault zone width and hydraulic conductivity on the early inflow (inflow prior to the lining and grouting) are investigated. The relationship between fracture density and hydraulic conductivity is also considered. The result of the study suggests that fault zone width has the greatest effect on groundwater inflow into the tunnel, and sandstone thickness, hydraulic conductivity and fracture density in order shows an influence on the inflow.

• Geomechanics and Engineering
• /
• v.21 no.4
• /
• pp.337-348
• /
• 2020

Tropical organic soils having more than 65% of organic matters are named "peat". This soil type is extremely soft, unconsolidated, and possesses low shear strength and stiffness. Different conventional and industrial binders (e.g., lime or Portland cement) are used widely for stabilisation of organic soils. However, due to many factors affecting the behaviour of these soils (e.g., high moisture content, fewer mineral particles, and acidic media), the efficiency of the conventional binders is low and/or cost-intensive. This research investigates the impact of different constituents of cement-sodium silicate grout system on the compressibility behaviour of organic soil, including settlement and void ratio. A microstructure analysis is also carried out on treated organic soil using Scanning Electron Micrographs (SEM), Energy Dispersive X-ray spectrometer (EDX), and X-ray Diffraction (XRD). The results indicate that the settlement and void ratio of treated organic soils decrease gradually with the increase of cement and kaolinite contents, as well as sodium silicate until an optimum value of 2.5% of the wet soil weight. The microstructure analysis also demonstrates that with the increase of cement, kaolinite and sodium silicate, the void ratio and porosity of treated soil particles decrease, leading to an increase in the soil density by the hydration, pozzolanic, and polymerisation processes. This research contributes an extra useful knowledge to the stabilisation of organic soils and upgrading such problematic soils closer to the non-problematic soils for geotechnical applications such as deep mixing.

• Geomechanics and Engineering
• /
• v.19 no.4
• /
• pp.343-352
• /
• 2019

For quality control and the economical design of grouted sand, the prior establishment of the unconfined compressive strength (UCS) estimating formula is very important. This study aims to develop an empirical UCS estimating formula for grouted sand based on the physical properties of sands and the UCS of cured pure grout. Four sands with varying particle sizes were grouted with both microfine cement and Ordinary Portland cement. Grouted specimens were prepared at three different relative densities and at three different water-to-cement ratios, and unconfined compression tests were performed. The results demonstrate that UCS of grouted sand can be expressed as the power function of the UCS of cured pure grout: $UCS_{grouted\;sand}/1MPa=A_{soil}{\cdot}(UCS_{pure}/1MPa)^N$. Because the exponent N strongly depends on the combination of pore area and pore size, N is expressed as the function of porosity (n) and specific surface ($S_a$). Additionally, because $S_a$ determines the area of the sand particle that cement particles can adsorb and n determines the number of cementation bondings between sand particles, $A_{soil}$ is also expressed as the function of n and $S_a$. Finally, the direct relationship between $A_{soil}$ and N is also investigated.

• Geomechanics and Engineering
• /
• v.11 no.1
• /
• pp.117-139
• /
• 2016

Previous studies for soil movements induced by tunneling have primarily focused on the free soil displacements. However, the stiffness of existing structures is expected to alter tunneling-induced ground movements, the sheltering influences for underground structures should be included. Furthermore, minimal attention has been given to the settings for the shield machine's operation parameters during the process of tunnels crossing above and below existing tunnels. Based on the Shanghai railway project, the soil movements induced by an earth pressure balance (EPB) shield considering the sheltering effects of existing tunnels are presented by the simplified theoretical method, the three-dimensional finite element (3D FE) simulation method, and the in-situ monitoring method. The deformation prediction of existing tunnels during complex traversing process is also presented. In addition, the deformation controlling safety measurements are carried out simultaneously to obtain the settings for the shield propulsion parameters, including earth pressure for cutting open, synchronized grouting, propulsion speed, and cutter head torque. It appears that the sheltering effects of underground structures have a great influence on ground movements caused by tunneling. The error obtained by the previous simplified methods based on the free soil displacements cannot be dismissed when encountering many existing structures.

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