• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.543-560
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• 2018

With the increased development in downtown underground space facilities that vertically cross under a railway at a shallow depth, the demand for non-open cut method is increasing. However, most construction sites still adopt the pipe roof method, where medium and large diameter steel pipes are pressed in to form a roof, enabling excavation of the inside space. Among the many factors that influence the loosening region and loads that occur while pressing in steel pipes, the size of the pipe has the largest impact, and this factor may correspond to the magnitude of load applied to the underground structure inside the steel pipe roof. The super equilibrium method (SEM) has been developed to minimize ground disturbance and loosening load, and uses small diameter pipes of approximately 114 mm instead of conventional medium and large diameter pipes. This small diameter steel pipe is called an SEM pile. After SEM piles are pressed in and the grouting reinforcement is constructed, a crossing structure is pressed in by using a hydraulic jack without ground subsidence or heaving. The SEM pile, which plays the role of timbering, is a fore-poling pile of approximately 5 m length that prevents ground collapse and supports surface load during excavation of toe part. The loosening region should be adequately calculated to estimate the spacing and construction length of the piles and stiffness of members. In this paper, we conducted a comparative analysis of calculations of loosening load that occurs during the press-in of SEM pile to obtain an optimal design of SEM. We analyzed the influence of factors in main theoretical and empirical formulas applied for calculating loosening regions, and carried out FEM analysis to see an appropriate loosening load to the SEM pile. In order to estimate the soil loosening caused by actual SEM-pile indentation and excavation, a steel pipe indentation reduction model test was conducted. Soil subsidence and soil loosening were investigated quantitatively according to soil/steel pipe (H/D).

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.593-608
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• 2018

If a problem occurs in the strut during the construction of the braced wall, they may cause excessive deformation of the braced wall. Therefore, in this study, the behavior of the braced wall and existing tunnel adjacent to excavation were investigated assuming that the support function of strut is lost during construction process. For this purpose, a series of model test was performed. As a result of the study, the earth pressure in the ground behind wall was rearranged due to the deformation of the braced wall, and the ground displacements caused the deformation of adjacent tunnels. When the struts located on the nearest side wall from the tunnel were removed, the deformation of the braced wall and the tunnel deformation were the largest. The magnitude of transferred earth pressure depended on the location of tunnel. The increase of the cover depth of tunnel from 0.65D to 2.65D caused the increase of the earth pressure by 25.6%. As the distance between braced wall and tunnel was increased from 0.5D to 1.0D, the transferred earth pressure increased by 16% on average. Horizontal displacements of braced wall by the removal of the strut tended to concentrate around the removed struts, and the horizontal displacement increased as the strut removal position is lowered. The tunnel displacement was maximum, when the cover depth of tunnel was 1.15D and the horizontal distance between braced wall and the side of tunnel was 0.5D. The minimal displacement occurred, when the cover depth of tunnel was 2.65D and the horizontal distance between braced wall and the side of tunnel was 1.0D. The difference between the maximum displacement and the minimum displacement was about 2 times, and the displacement was considered to be the largest when it was in the range of 1.15D to 1.65D and the horizontal distance of 0.5D.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.375-388
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• 2017

In order to solve the traffic congest and environmental issues, small-cross section tunnel for small car only is increasing, but there is not standard for installation of disaster prevention facility. In this study, in order to investigate the behavioral characteristics of thermal environment and smoke in a small cross section tunnels with a large port exhaust ventilation system, the A86, the U-Smartway and the Seobu moterawy tunnel, Temperature and CO concentration in case of fire according to cross sectional area, heat release rate and exhaust air flow rate were analyzed by numerical analysis and the results were as follows. As the cross-sectional area of the tunnel decreases, the temperature of the fire zone increases and the rate of temperature rise is not significantly affected by heat release rate. However, there is a difference depending on the change of the exhaust air flow rate. In the case of applying the exhaust air flow rate $Q_3+2.5Ar$ of the large port exhaust ventilation system, the temperature of the fire zone was 7.1 times for A86 ($Ar=25.3m^2$) and 5.4 time for U-smartway ($Ar=37.32m^2$) by Seobu moterway tunnel ($Ar=46.67m^2$). The CO concentration of fire zone also showed the same tendency. The A86 tunnels were 10.7 times and the U-Smartways were 9.5 times more than the Seobu moterway. Therefore, in the case of a small section tunnel, the thermal environment and noxious gas concentration due to the reduction of the cross-sectional area are expected to increase significantly more than the cross-sectional reduction rate.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.421-435
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• 2017

Recently, due to the saturation of ground structures and the overpopulation of pipeline facilities requires to development of underground structures as an alternative to ground structures. Thus, mechanized tunnel construction of the shield TBM method has been increasing in order to prevent vibration and noise problems in construction of the NATM tunnel for the urban infrastructure construction. Tunnel construction plan for the tunnel line should be formed in a sharp curve to avoid building foundation and underground structures and it is inevitable to develop a shield TBM technology that suits the sharp curve tunnel construction. Therefore, this study is about the structural stability technology of the articulation jack, shield jack and skin plate for the shield TBM thrust in case of the mechanized tunnel construction that is a straight and sharp curve line. The construction case study and shield TBM operation principle are examined and analyzed by the theoretical approach. The torque of the cutter head, the thrust of the articulation jack and the shield jack, the amount of over cutting for curve is important respectively in shield TBM construction of straight and sharp curve line. In addition, it is very important to secure the stability of the skin plate structure to ensure the safety of the inside worker. This study examines the general structure and construction of the equipment, experimental simulation was carried out through numerical analysis to examine the main factors and structural stability of the skin plate structure. The structural stability of the skin plate was evaluated and optimizes the shape by comparing the loads of the articulation jack by selecting the virtual soil to be applied in a straight and sharp curve line construction. Since the present structure and operation method of the shield TBM type in domestic constructions are very similar, this study will help to develop the localized shield TBM technology for the new equipment and the vulnerability and stability review.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.347-365
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• 2020

In order to resolve traffic problems in urban areas and to increase the area of green spaces, tunnels in downtown areas are being increased. Additionally, the application of large port smoke extraction ventilation systems is increasing as a countermeasure to smoke extraction ventilation for tunnels with high potential for traffic congestion. It is known that the smoke extraction performance of the large port smoke extraction system is influenced not only by the amount of the extraction flow rate, but also by various factors such as the shape of the extraction port (damper) and the extraction air velocity through a damper. Therefore, in this study, the design standards and installation status of each country were investigated. When the extraction air flow rate was the same, the smoke extraction performance according to the size of the damper was numerically simulated in terms of smoke propagation distance, compared and evaluated, and the following results were obtained. As the cross-sectional area of the smoke damper increases, the extraction flow rate is concentrated in the damper close to the extraction fan, and the smoke extraction rate of the damper in downstream decreases, thereby increasing the smoke propagation distance on the downstream side. In order to prevent such a phenomenon, it is necessary to reduce the cross-sectional area of the smoke damper and increase the velocity of passing air through the damper so that the pressure loss passing through the damper increases, thereby reducing the non-uniformity of smoke extraction flow rate in the extraction section. In this analysis, it was found that when the interval distance of the extraction damper was 50 m, the air velocity passing through damper was 4.4 m/s or more, and when the interval distance of the extraction dampers was 100 m, the air velocity passing through damper was greater than 4.84 m/s, it was found to be advantageous to ensure smoke extraction performance.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.669-683
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• 2017

The objective of this study is to propose a modification of the previously proposed drainage system for catching the partial leakage of underground concrete structures. Two techniques were proposed for applying the drainage system only to the leaking parts. One was for conveying leaking groundwater to the collection point in the drainage system and the other was for conveying the collected groundwater to the primary drainage system of the underground concrete structure. Four waterproofing materials for conveying leaking groundwater to the catchment point of the drainage system, Durkflex made of porous rubber material, KE-45 silicone adhesive with super strong adhesion, Hotty-gel made of polymeric materials and general silicone adhesive were evaluated for waterproofing performance. Hotty-gel only showed perfect waterproof performance and the other three waterproof materials leaked. The modified drainage system with Hotty-gel and drainage pipe with fixed saddle to convey the leaking groundwater from the catchment point to the primary drainage system were tested on the concrete retaining wall. The waterproof performance and the drainage performance were evaluated by injecting 1,000 ml of water in the back of the modified drainage system at the 7-day, 14-day, 21-day, 28-day, 2-month and 3-month. There was no problem in waterproof performance and drainage performance of the modified drainage system during 3 months. In order to evaluate the construction period and construction cost of the modified drainage system, it was compared with the existing leaching repair method in surface cleaning stage, leakage treatment stage, and protective barrier stage. Total construction period and construction cost were compared in considering the contents of work, repair material, construction equipment, working time, and total number of workers. As a result of comparing and analyzing in each construction stage, it was concluded that the modified drainage system could save construction period and construction cost compared to the existing leaching repair method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.855-867
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• 2018

When a weak zone exists ahead of tunnel face, the stress in the adjacent area would increase due to the longitudinal arching effect and the stability of the tunnel is affected. Therefore, it is critical to prepare a countermeasure through the investigation of the frontal weakness zone of the excavated face. Although there are several researches to predict the existence of weak zone ahead of tunnel face, such as geophysical exploration, numerical analysis and tunnel support, lack of studies on the relaxation zone depending on the width or distance from the vulnerable area. In this study, the impact of the weak zone on the formation of the relaxation zone was investigated. For this purpose, a series of laboratory test were carried out varying the width of the weak zone and the separation distance between tunnel face and weak zone. In the model test, sand with a water content of 3.8% was used to form a model ground. The model weak zone was constructed with dry sand curtains. The tunnel face was adjusted to allow a sequential excavation of upper and lower half part. load cells were installed on the bottom of the foundation and the tunnel face and measuring instruments for displacement were installed on the surface of the model ground to measure the vertical stress and surface displacements due to tunnel excavation respectively. The test results show that the width of weak zone did not affect the ground settlement while the ground subsidence drastically increased within 0.25D. The vertical stress and horizontal stress increased from 0.5D or less. In addition, the longitudinal arching effect is likely within the 1.0D zone ahead of the tunnel face, which may reduce the vertical stress in the ground following tunneling direction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.5
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• pp.591-610
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• 2020

Concrete with activated carbon and titanium dioxide (TiO₂) has been used to reduce the particulate matter (PM) in underground structures (e.g., tunnels) due to the high performance of nitrogen oxides (NOx) abatement. Damage (e.g. crack, spalling, or detachment) can be caused by the environmental and ageing effects on the surface of the particulate matter reduction concrete, installed on the tunnel lining. Therefore, it is important to evaluate the existence of spalling on the concrete surface for maintaining performance of NOx reduction. In this study, a basic research was performed for feasibility of spalling evaluation using electrical resistivity characteristics. Given the test results, the electrical resistivity was decreased as the ratios of activated carbon (0~15%) and TiO₂ (0~25%) were increased for specimens. Under a dry condition, electrical resistivity of cement specimens, mixed with activated carbon and TiO₂, was decreased up to 2.3 times, compared with the normal cement specimen. In addition, under saturation conditions (degree of saturation: 85~98%), electrical resistivity of cement specimens with activated carbon, was decreased up to 3.5 times, compared with the normal cement specimen. Regardless of the condition (dry or saturated), the difference of electrical resistivity values shows the range of 2.3~2.8 times between the mixing specimen (with activated carbon (15%) and TiO₂ (25%)) and the normal cement specimen. This study can help to provide basic knowledge for spalling evaluation using the electrical resistivity on the surface of the particulate matter reduction concrete in tunnels.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.5
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• pp.505-522
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• 2013

Previously, a new concept of indexing methodology has been proposed for quantitative assessment of tunnel collapse hazard level at each tunnel face with respect to the given geological data, design condition and the corresponding construction activity (Shin et al, 2009a). In this paper, 'linear' model, in which weights of influence factors are invariable, and 'non-linear' model, in which weights of influence factors are variable, are taken into account with some examples. Then, the 'non-linear' model is validated by using 100 tunnel collapse cases. It appears that 'non-linear' model allows us to have adapted weight values of influence factors to characteristics of given tunnel site. In order to make a better understanding and help for an effective use of the system, a series of operating processes of the system are built up. Then, by following the processes, the system is applied to a real-life tunnel project in very weak and varying ground conditions. Through this approach, it would be quite apparent that the tunnel collapse hazard indices are determined by well interlinked consideration of face mapping data as well as design/construction data. The calculated indices seem to be in good agreement with available electric resistivity distribution and design/construction status. In addition, This approach could enhance effective usage of face mapping data and lead timely and well corresponding field reactions to situation of weak tunnel faces.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.761-778
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• 2017

The need of the underground space for the infrastructures in urban area is increasing, and especially the demand for shallow tunnels increased drastically. It is very important that the shallow tunnel in the urban area should fulfill not only its own safety conditions but also the safety condition for the adjacent structures and the surrounding sub-structure. Most of the studies on the behavior of shallow tunnels concentrated only on their behaviors due to the local deformation of the tunnel, such as tunnel crown or tunnel sidewall. However, few studies have been performed for the behavior of the shallow tunnel due to the deformation of the entire tunnel. Therefore, in this study the behavior of the surrounding ground and the stability caused by deformation of the whole tunnel were studied. For that purpose, model tests were performed for the various ground surface slopes and the cover depth of the tunnel. The model tunnel (width 300 mm, height 200 mm) could be simulationally deformed in the vertical and horizontal direction. The model ground was built by using carbon rods of three types (4 mm, 6 mm, 8 mm), in various surface slopes and cover depth of the tunnel. The subsidence of ground surface, the load on the tunnel crown and the sidewall, and the transferred load near tunnel were measured. As results, the ground surface subsided above the tunnel, and its amount decreased as the distance from the tunnel increased. The influence of a tunnel ceased in a certain distance from the tunnel. At the inclined ground surface, the wider subsidence has been occurred. The loads on the crown and the sidewall were clearly visible, but there was no effect of the surface slope at a certain depth. The load transfer on the adjacent ground was larger when the cover depth (on the horizontal surface) was lager. The higher the level (on the inclined surface), the wider and smaller it appeared. On the shallow tunnel under inclined surface, the transfer of the ambient load on the tunnel sidewall (low side) was clearly visible.