• Explosives and Blasting
• /
• v.38 no.4
• /
• pp.26-36
• /
• 2020

With the increase of expansion and use of the underground space, the possibility of an underground explosion by terrorists is increasing. In this study, after modeling a circular tunnel excavated at a depth of 50m, an explosion load was applied to the inside of the tunnel. As for the explosion load, the explosion load of the maximum explosive amount for six types of vehicle booms proposed by ATF (Bureau of Alcohol, Tobacco, and Firearms) was calculated. For the rock mass around the circular tunnel, three types of rock grades were selected according to the support pattern suggested in the domestic tunnel design. Nonlinear dynamic analysis was performed to evaluate the influence of the ground structure by examining the surface displacement using the explosion load and rock mass characteristics as parameters. As a result of the analysis, for grade 1 rock, the influence on the uplift of the surface should be considered, and for grade 2 and 3 rocks, the influence on a differential settlement should be considered. In particular, for grade 3 rocks, detailed analysis is required for ground-structure interaction within 40m. Also, it is considered that the influence of Young's modulus is the main factor for the surface displacement.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.2
• /
• pp.105-116
• /
• 2010

The estimation of surface settlement, ground behavior and tunnel displacement are the main factors in urban tunnel design with shallow depth and unconsolidated soil. On deformation analysis of shallow tunnel, it is important to identify possible deformation mechanism of shear bands developing from tunnel shoulder to the ground surface. This paper investigated the effects of key design parameter affecting deformation behavior by numerical analysis using nonlinear model incorporating the reduction of shear stiffness and strength parameters with the increment of the maximum shear strain after the initiation of plastic yielding. Numerical parametric studies are carried out to consider the reduction of shear stiffness and strength parameters, horizontal stress ratio, cohesion and shotcrete thickness.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.5
• /
• pp.369-378
• /
• 2010

This paper presents a new approach of closing the tunnel face with sprayed concrete to reduce the stress at the tunnel face and displacement occurring at the ground surface during tunnel excavation. In order to carry out this research, the experimental and numerical studies are performed. In the experimental study, the model tests are carried out according to the closure ratio of tunnel face, tunnel depth and tunnel excavation length. The model test results are analyzed and interpreted by numerical calculation in order to verify both results obtained from experimental and numerical studies. It is clearly found that the tunnel face stability is decreased in decreasing the closure ratio of tunnel face. The results also show that the tunnel face is stable when the closure ratio of tunnel face is larger than 80%. This research will be very useful to develop the economical tunnel face closing system.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.2
• /
• pp.145-155
• /
• 2010

Recently interest in subsea tunnels is increasing nationwide and the construction of a subsea tunnel is taking place. For the stability of such a subsea tunnel, grouting is necessary for the water barrier and reinforcement of the tunnel. In this study, therefore, it was investigated how the grouting reinforcement had an effect on the stability of a subsea tunnel located in a great depth. To this end, Hydro-mechanical coupled analyses were performed for a sensitivity analysis in terms of different grouting range, rock class, shotcrete thickness, coefficient of lateral earth pressure, grouting thickness, and pumping existence for the rock classes I, III, and V. FLAC-2D ver. 5.0 was used for the numerical analyses. It was came to the conclusion that the effect of the increased water pressure due to the water barrier of the grouting should be considered as well as the strength improved effect in designing grouting reinforcement of subsea tunnels.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.11 no.3
• /
• pp.255-264
• /
• 2009

This paper concerns the behavior of 2-Arch tunnel constructed under various conditions. A 2-Arch tunnel section adopted in a subway tunnel construction site is considered in this study. A calibrated 3D finite element model was adopted to conduct parametric studies on a variety of construction scenarios including lagged distance between left and right tunnels, overburden, and geological condition. The results of analyses were examined in terms of crown settlement, shotcrete lining stress, and load on center column in relation to the lagged distance, cover depth, and the ground condition. The results indicate that the shotcrete lining stress and the center pillar load are more influenced by the second tunnel excavation than the tunnel deformation. Also shown is that a greater lagged distance is required to minimize the interaction between two tunnels when the ground condition becomes weaker. Fundamental mechanisms of 2-arch tunnel were also discussed based on the results.

• Journal of the Korean Geotechnical Society
• /
• v.40 no.2
• /
• pp.7-17
• /
• 2024

Vibrations were measured at the surface of a GTX-A site to assess the impact of blasting on underground tunneling. A numerical analysis was conducted using the same ground and blast conditions as those at the site, accompanied by a comparative analysis of other GTX-A sites. This analysis determined the maximum vibration velocity at regular intervals directly above the blasting point at each site. The results were compared with domestic and international vibration standards to establish the vibration measurement range. The specified vibration measurement locations in domestic regulations—"measuring from the closest part of the structure's foundation to the blasting source, and if conditions make it impossible, measuring from the nearest surface to it"—were evaluated. Furthermore, this study underscores the significance of considering the tunnel drilling depth and soil conditions when selecting a vibration measurement location.

• The Journal of Engineering Geology
• /
• v.28 no.1
• /
• pp.69-79
• /
• 2018

The Korean government attempts to reduce $CO_2$ emissions by 37% to 314.7 Mt $CO_2$, down from the estimated 850.6 Mt $CO_2$ until 2030 in order to confront green house effect. In this context, in 2014, Korean government launched $CO_2$ Storage Environmental Management Research (K-COSEM) Center for carrying out pilot-scale research on $CO_2$ leakage from underground $CO_2$ storage facilities. For the detection of $CO_2$ leakage, it is necessary to identify hydrologeological and geophysical characteristics of the subject area. In the study site of Naesan-ri, Daeso-myeon, Eumseong-gun, Chungbuk Province, two times injection tests (June 28-July 24, 2017 and August 07-September 11, 2017) of $CO_2$ and $SF_6$ dissolved waters, respectively, was conducted to understand the leakage behavior of $CO_2$ from underground. The injection well was drilled to a depth of 24 m with a 21-m casing and screen interval of 21~24 m depth. Two times resistivity surveys on August 18, 2017 and September 1, 2017, were conducted for revealing the flow of the injected water as well as the electrical properties of the study site. The study results have shown that the high-resistivity zone and the low-resistivity zone are clearly contrasted with each other and the flow direction of the injected water is similar to natural groundwater flow. Besides, the low resistivity zone is widely formed from the depth of injection to the shallow topsoil, indicating that the weathered zone of high permeability has high $CO_2$ leakage potential.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.2
• /
• pp.119-128
• /
• 2008

In the case of a circular shaft, it is expected that asymmetric loads should apply on the surface rather than symmetric loads due to geographical factors and the non-homogeneity of the jointed rock masses. In this study, discontinuous numerical analysis was carried in order to analyze the characteristics of asymmetric load distribution on the wall of the circular shaft due to anisotropy caused by heterogeneity of rock masses affected by the discontinuities like as a Joint. And it was also analyzed that the effect of the mechanical properties varied with the rock mass rating and horizontal stress with depth had influence in the asymmetric load on the wall of the shaft. In the case of considering the effect of the joint as variable, asymmetric load ratio $(R_p)$, which was defined as the ratio of the load subtracted minimum from maximum to minimum, was below 25% in the hard rock. As regarding the variation of the rock mass rating with depth as variable, the value of $R_p$ was below than 25% in the hard rock, and the value between 30% and 40% in the soft rock. On the other hand, the $R_p$ of fractures rock was between $45{\sim}50%$ which value was much higher than that in better rock mass rating.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.2
• /
• pp.485-500
• /
• 2018

The behavior of cement-based permeation grouting is divided into three different groups depending on the grain size distribution of the soils: (1) zone of cement-based permeation grouting not feasible; (2) zone of cement-based permeation grouting feasible; and (3) zone in which an accelerating agent should be added to limit the penetration depth. In the cement-based permeation grouting feasible zone, the concept of a representative pore radius was proposed. The ratios of the representative pore radius to the mean pore radius were obtained by performing laboratory test and comparing with clogging theory; these values were in the range of 1.07 and 1.35 depending on the grain size distribution of the soils. In addition, a functional relationship between the lumped parameter (${\theta}$), the representative pore radius and the w/c ratio were derived by comparing and matching experimental results with predictions from theory. In the zone in which the accelerating agent should be added, the controlling process of gel time to limit the penetration depth was experimentally verified. The test results matched well with those obtained from theory utilizing the developed grout penetration program on condition that the viscosity increasing tendency of grout suspension with time is properly taken into account.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.6
• /
• pp.735-747
• /
• 2019

Due to the lack of ground space by urbanization, the demand of utility tunnels for laying social facilities is increasing. During the construction of a utility tunnel in downtown area using a shield TBM, various problems may occur when difficult ground is encountered such as mixed ground and cobbly ground. Thus, in this study, using MIDAS GTS NX (Ver. 280), a numerical analysis was performed on characteristics of difficult ground, reinforced area, depth of cover and groundwater level to analyze the optimal ground reinforced area according to combination of parameters. As a result, it was difficult to secure stability in unconstrained excavation cases on both the mixed ground and the cobbly ground. However, when ground reinforcement grouting as much as 2.0D is applied, convergence occurred within the allowable limit, except for mixed ground with a depth of cover 30 m. In addition, excessive leakage occurred during excavation of both the mixed ground and the cobbly layers. It was able to secure stability after applying waterproof grouting.