• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.3
• /
• pp.489-501
• /
• 2017

The collapse accidents during a open ground excavation in urban areas not only lead to human injuries and material damages in the construction site, but also lead to road sinks and damages to the adjacent facilities due to settlement of ground around the construction site. Therefore, during a open ground excavation in the urban areas, it is necessary to thoroughly prepare for prevention of collapse accidents, and consider whole construction stage such as planning, design and construction. In this study, the priorities to be managed mainly were obtained in order to prevent collapse accidents during a open ground excavation. After analyzing results from past accidents cases for open ground excavations, priorities were evaluated regarding collapse-inducing elements using the Delphi technique which is a decision-making method by consensus among experts. As a result, insufficient groundwater treatment, bad geotechnical investigation and instability on construction, etc. were obtained as priorities for prevention of collapse accidents.

• Journal of Industrial Technology
• /
• v.27 no.B
• /
• pp.209-214
• /
• 2007

This paper is the research result about centrifuge model experiments of investigating the behavior of bridge abutment on the sloped ground. Ground condition of the studied site was the bridge abutment with pile foundation adjacent to the slope. The pile foundations was supported on the soft rocks covered with the embankment. Evaluating the behavior of such a complicate ground and structure conditions was not easy so that the centrifuge modelling was performed to find the overall behavior of them. Layout of centrifuge model experiment was simplified to simulate easily the actual behavior of very complicate site condition. Construction process in field such as ground excavation for footing foundation, installation of piles, placement of footing and bridge abutment, backfilling and surcharge loading eas duplicated in the centrifuge model experiment. Consequently, the stability of the piled bridge abutment adjacent to the slope of embankment was evaluated throughout centrifuge modelling.

• Geomechanics and Engineering
• /
• v.30 no.6
• /
• pp.565-577
• /
• 2022

In this study, a series of three-dimensional numerical parametric study was conducted to investigate deformation mechanisms of an existing box culvert due to an adjacent multi-propped basement excavation in clays. Field measurements from an excavation case history are first used to calibrate a baseline Hardening Soil Small Strain (HS-small) model, which is subsequently adopted for parametric study. Results indicate that the basement-box culvert interaction along the basement centerline can be considered as a plane strain condition when the length of excavation (L) reaches 14 H_e (i.e., final excavation depth). If a plane strain condition (i.e., L/H_e=12.0) is assumed for analyzing the basement-box culvert interaction of a short excavation (i.e., L/H_e=2.0), the maximum settlement and horizontal movement of the box culvert are overestimated significantly by up to 15.7 and 5.1 times, respectively. It is also found that the deformation of box culvert can be greatly affected by the basement excavation if the distance between the box culvert and retaining wall is less than 1.5 H_e. The induced deformation in the box culvert can be dramatically reduced by improving the ground inside the excavation or implementing other precautionary measures. For example, by adding jet grouting columns within the basement and installing an isolation wall behind the retaining structures, the maximum settlements of box culvert are shown to reduce by 37.2% and 13.4%, respectively.

• The Journal of the Convergence on Culture Technology
• /
• v.6 no.4
• /
• pp.669-675
• /
• 2020

In this study, 3D analysis was compared in evaluating the track deformation of subway structures during adjacent excavation. For the 3D analysis model, the boundary conditions of the tunnel model and the application level of the ground water were analyzed as variables. As the result of the effects of track irregularity using the 3D model, the analysis model considering the site ground water level instead of the design values and changing the constraint of the boundary condition is more reasonable. In addition, the influence of track irregularity due to the boundary condition and load condition of the analytical model is more obvious in the factors directly affected by the longitudinal relative displacement of the rail, such as alignment, cross level and gauge irregularity. Therefore, the evaluation on track stability according to adjacent excavation work was appropriate to analysed the longitudinal deformation of the track by using 3D model that could be investigate the deformation of rail. In addition, the boundary condition and load condition(ground water level) of the numerical model was important for accurate analysis results.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.26 no.1
• /
• pp.59-78
• /
• 2024

In tunnel construction, the stability is evaluated by the settlement of adjacent structures and ground, but the shear strain of the ground is the main factor that determines the failure mechanism of the ground due to the tunnel excavation and the change of the operating load, and can be used to review the stability of the tunnel excavation and to calculate the reinforcement area. In this study, a twin tunnel excavation was simulated on a soft ground in an urban area through a laboratory model test to analyze the behavior of the twin tunnel excavation on the adjacent pile grouped foundation and adjacent ground. Both the displacement and the shear strain of ground were obtained using a close-range photogrammetry during laboratory model test. In addition, two-dimensional finite element numerical analysis was performed based on the model test. The results of a back-analysis showed that the maximum shear strain rate tends to decrease as the horizontal distance between the pillars of the twin tunnel and the vertical distance between the toe of the pile group and the crown of the tunnel were decreased. The impact of the second tunnel on the first tunnel and pile group was decreased as the horizontal distance between the pillars of the twin tunnel was increased. In addition, the vertical distance between the toe of the pile group and the crown of the tunnel had a relatively greater impact on the shear strain results than the horizontal distance of the pillars between the twin tunnels. According to the results of the close-range photogrammetry and numerical analysis, the settlement of adjacent pile group and adjacent ground was measured within the design criteria, but the shear strain of the ground was judged to be outside the range of small strain in all cases and required reinforcement.

• Geomechanics and Engineering
• /
• v.21 no.2
• /
• pp.111-122
• /
• 2020

In most cases in urban areas, construction of divergence tunnel should take into account proximity to existing tunnel in operation. This inevitably leads to deformation of adjacent structures and surrounding ground. Preceding researches mainly dealt with reinforcing of the diverging section for the stability including the pillar. This has limitations in investigating the interactive effects between existing structures and surrounding ground due to the excavation of the divergence tunnel. In this study, the complex interactive behavior of pile, the operating tunnel, and the surrounding ground according to horizontal offsets between the two adjacent tunnels was quantitatively analyzed based on conditions diverged from operating tunnel in urban areas. The effects on ground structures confirmed by analyzing the ground surface settlements, pile settlements, and the axial forces of the pile. The axial forces of lining in operating tunnel investigated to estimate their impact on existing tunnel. In addition, in order to identify the deformation of the surrounding ground, the close range photogrammetry applied to the laboratory model test for confirming the underground displacements. Two-dimensional finite element numerical analysis was also performed and compared with the results. It identified that the impact of excavating a divergence tunnel decreased as the horizontal offset increased. In particular, when the horizontal offset was larger than 1.0D (D is the diameter of operating tunnel), the impact on existing structures further reduced and the deformation of surrounding ground was concentrated at the top of the divergence tunnel.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.5
• /
• pp.15-26
• /
• 2003

Urban excavation requires highly reliable prediction technique for the design and construction of earth retaining structure in order to protect adjacent structures around deep excavation. Application of the pre-loading of bracing for deep excavation has been reported, and the known beneficial effects are not fully understood and recognized by many practitioners. Model tests have been carried out to evaluate the efficiency of pre-loading system in reducing ground settlement as well as prediction of structural damage around excavation in sand. The test results revealed that the applied pre-loading of 50% and 70% showed about 20% of reduction in horizontal wall displacement and 30∼40% reduction in ground settlement. Also, bracing forces and earth pressure distribution behind the wall have been monitored during pre-loading at various excavation stages.

• Tunnel and Underground Space
• /
• v.12 no.3
• /
• pp.179-188
• /
• 2002

This study is to understand the effect of the vibration and the stress changes due to the excavation of 2 arch parts of a tunnel, which is a Gyungbu Express Railway tunnel, on the tunnel itself and adjacent slopes in advance, and to analyze the stability. For the estimation of ground conditions, borehole tests, borehole camera logging and seismic logging were performed. Ground properties at a specific location were determined as input constants by performing 2 dimensional analyses with possible ranges of uncertain ground properties. Static and pseudo-static (due to blasting vibration) factors of safety were calculated. The behavior of the tunnel and its vicinity due to the tunnel excavation were predicted by 3 dimensional analyses. It was also tested whether the support system was proper.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.03a
• /
• pp.657-664
• /
• 2002

This study presents the influence of blasting-induced vibration on the adjacent structures in rocks of various RMR values. 3D finite element analysis was performed to simulate the behaviour of tunnel and adjacent structures during rock excavation. The blast loadings were evaluated from the blasting pressure which is depending on the type and amount of explosive charges. Influencing factors for the stability of adjacent structures and ground conditions were reviewed in terms of structural dimensions and RMR values. The stiffness and load of adjacent structures are modeled in the numerical analysis to Investigate blasting effects of the size of adjacent structures. The vibration velocity and maximum particle velocity was increase sharply when the RMR value changed from 30 to 50. The effect of particle velocity was minimized at the width of structure become 2 times of tunnel diameter.

• Geomechanics and Engineering
• /
• v.14 no.4
• /
• pp.315-324
• /
• 2018

With rapid economic growth, numerous deep excavation projects for high-rise buildings and subway transportation networks have been constructed in the past two decades. Deep excavations particularly in thick deposits of soft clay may cause excessive ground movements and thus result in potential damage to adjacent buildings and supporting utilities. Extensive plane strain finite element analyses considering small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by diaphragm walls and bracings. The excavation geometrical parameters, soil strength and stiffness properties, soil unit weight, the strut stiffness and wall stiffness were varied to study the wall deflection behaviour. Based on these results, a multivariate adaptive regression splines model was developed for estimating the maximum wall deflection. Parametric analyses were also performed to investigate the influence of the various design variables on wall deflections.