• Journal of the Korean GEO-environmental Society
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• v.12 no.11
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• pp.39-49
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• 2011

In this paper it was focused on the characteristics of displacement and stress due to the construction of diagonal twin tunnel. In this research, the characteristics have been analyzed with the presumption that the tunnel's diameter (D) is 13m and the ground was formed by weathered rock. In analysis, the width of pillar is 2.0D, 2.5D, 3.0D, the height of soil cover is 3D, 4D, 5D, and the installation angle of diagonal twin tunnel has been changed into $15^{\circ}$, $30^{\circ}$, $45^{\circ}$. And the program used in this analysis is FLAC which is widely used in solution problems of ground engineering in order to gain and analyze occurring shotcrete and rockbolt stress and nearby ground displacement according to pillar width, the height of soil cover and installation angle of diagonal twin tunnel. As a result, in the weathered rock grounds, when the width of pillar is more than 2.0D, the height of soil cover is over 5.0D, and the installation angle of diagonal twin tunnel is lower, they lessen effects on the ground and favorable on the stability of tunnel.

• Tunnel and Underground Space
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• v.23 no.2
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• pp.110-119
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• 2013

It is generalized to measure the arch settlement and convergence during tunnel construction for monitoring its mechanical stability. The initial convergence rate a day is defined from the first convergence measurement and the final convergence defined as the convergence measured lastly. The initial and the final tunnel arch settlement are defined like the preceding convergence. In the study, the relations between the initial and final displacements of a shallow tunnel are analyzed. The measurements were performed in the tunnel of subway 906 construction site in Seoul. The overburden is 10-20 m and the tunnel goes through weathered soil/rock. The width and height of the tunnel are about 11.5 m, 10m, respectively. So this is a shallow tunnel in weak rock. The length of tunnel is about 1,820 m and the tunnel was constructed in 2 stages, dividing upper and lower half. The numbers of measurement locations of arch settlement and convergence are 184 and 258, respectively. As a result, the initial displacement rate and the final displacement are comparatively larger in the section of weathered soil.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.563-573
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• 2024

In this study, various countermeasures used to mitigate tunnel deformations due to nearby multi-propped basement excavation in soft clay are explored by three-dimensional numerical analyses. Field measurements are used to calibrate the numerical model and model parameters. Since concrete slabs can constrain soil and retaining wall movements, tunnel movements reach the maximum value when soils are excavated to the formation level of basement. Deformation shapes of an existing tunnel due to adjacent basement excavation are greatly affected by relative position between tunnel and basement. When the tunnel is located above or far below the formation level of basement, it elongates downward-toward or upward-toward the basement, respectively. It is found that tunnel movements concentrate in a triangular zone with a width of 2 H_e (i.e., final excavation depth) and a depth of 1 D (i.e., tunnel diameter) above or 1 D below the formation level of basement. By increasing retaining wall thickness from 0.4 m to 0.9 m, tunnel movements decrease by up to 56.7%. Moreover, tunnel movements are reduced by up to 80.7% and 61.3%, respectively, when the entire depth and width of soil within basement are reinforced. Installation of isolation wall can greatly reduce tunnel movements due to adjacent basement excavation, especially for tunnel with a shallow burial depth. The effectiveness of isolation wall to reduce tunnel movement is negligible unless the wall reaches the level of tunnel invert.

• Geomechanics and Engineering
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• v.12 no.2
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• pp.185-195
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• 2017

With the rapid development of urban underground traffic, the study of soil deformation induced by subway tunnel construction and its settlement prediction are gradually of general concern in engineering circles. The law of soil displacement caused by shield tunnel construction of adjacent buildings is analyzed in this paper. The author holds that ground surface settlement based on the Gauss curve or Peck formula induced by tunnel excavation of adjacent buildings is not reasonable. Integrating existing research accomplishments, the paper proposed that surface settlement presents cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics when the tunnel is respectively under buildings, within the scope of the disturbance and outside the scope of the disturbance. Calculation formulas and parameters on cork distribution curve and skewed distribution curve were put forward. The numerical simulation, experimental comparison and model test analysis show that it is reasonable for surface settlement to present cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics within a certain range. The research findings can be used to make effective prediction of ground surface settlement caused by tunnel construction of adjacent buildings, and to provide theoretical guidance for the design and shield tunnelling.

• Geomechanics and Engineering
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• v.19 no.3
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• pp.283-293
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• 2019

Evaluating the stability of the excavation face of the cross-river shield tunnel with good accuracy is considered as a nonlinear and multivariable complex issue. Understanding the stability evaluation method of the shield tunnel excavation face is vital to operate and control the shield machine during shield tunneling. Considering the instability mechanism of the excavation face of the cross-river shield and the characteristics of this engineering, seven evaluation indexes of the stability of the excavation face were selected, i.e., the over-span ratio, buried depth of the tunnel, groundwater condition, soil permeability, internal friction angle, soil cohesion and advancing speed. The weight of each evaluation index was obtained by using the analytic hierarchy process and the entropy weight method. The evaluation model of the cross-river shield construction excavation face stability is established based on the idea point method. The feasibility of the evaluation model was verified by the engineering application in a cross-river shield tunnel project in China. Results obtained via the evaluation model are in good agreement with the actual construction situation. The proposed evaluation method is demonstrated as a promising and innovative method for the stability evaluation and safety construction of the cross-river shield tunnel engineerings.

• Structural Engineering and Mechanics
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• v.84 no.5
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• pp.699-706
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• 2022

Settlement control techniques are critical for the safety of shield tunnel constructions, especially for facing complex situations. In this study, the shield tunnel structure from Huaita east road station to Heping Road station in Xuzhou metro No.3 line (China) is taken as engineering background, which has various complex problems of the upper-soft and lower-hard composite stratum conditions, twin curve shield tunnels, and underpass the foundation of the piled raft. The deformation characteristics of shield tunnelling passing through buildings are explored. Subsequently, comprehensive research methods of numerical simulation and field measurement are adopted to analyzing the effectiveness of settlement control by using the top grouting technique. The results show that the settlement of the buildings has obvious spatial characteristics, and the hysteresis effect can be obviously observed in soil deformation caused by shield construction. Meanwhile, the two shield constructions can cause repeated disturbances, reducing the soil deformation's hysteresis effect. Moreover, the shield tunnel's differential settlement is too large when a single line passes through, and the shield construction of the outer curve can cause more significant disturbance in the tunnel than the inside curve. Notably, the proposed process control parameters and secondary topgrouting method can effectively control the deformation of the shield tunnel, especially for the long-term deformation.

• Journal of the Korean Geotechnical Society
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• v.25 no.7
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• pp.11-21
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• 2009

This paper presents a new high-performance supporting system of the shallow tunnel. In order to perform this research the mechanism of new supporting system is suggested and compared with the conventional existing supporting system. It is found that the new supporting system as pre-support system has several advantages such as improvement of ground before tunnel excavation and increment of capacity of the tunnel support. The construction procedures of this supporting system are also reviewed. In addition, the numerical simulation is carried out to evaluate the new supporting system. It is found that the new high-performance supporting system is very applicable in shallow depth tunnel such as portal area, tunnel in soil and weak zone, and so on.

• Computers and Concrete
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• v.29 no.2
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• pp.69-79
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• 2022

For long underground box utility tunnels, post-tensioned precast concrete is often used. Between precast tunnel segments, sealed waterproof flexible joints are often specified. Fault displacement can lead to excessive deformation of the joints, which can lead to reduction in waterproofing due to diminished contact pressure between the sealant strip and the tunnel segment. This paper authenticates utilization of a finite element model for a prefabricated tunnel fault-crossing founded on ABAQUS software. In addition, material parameter selection, contact setting and boundary condition are reviewed. Analyzed under normal fault action are: the influence of fault displacement; buried depth; soil friction coefficient, and angle of crossing at the fault plane. In addition, distribution characteristics of the utility tunnel structure for vertical and longitudinal/horizontal relative displacement at segmented interface for the top and bottom slab are analyzed. It is found that the effect of increase in fault displacement on the splice joint deformation is significant, whereas the effects of changes in burial depth, pipe-soil friction coefficient and fault-crossing angle on the overall tunnel and joint deformations were not so significant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.772-775
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• 2005

Most engineers, related to soil and civil dynamic field, have been interested in the direct dynamic design of building transmitted from soil and rock to structure due to blasting. However it is not easy to estimate the dynamic response of structures due to blasting by using analytical method because of difficulties of soil modeling, prediction of excitation force and so on. In this paper, dynamic analysis have been performed to predict vibration level and evaluate dynamic safety of structure adjacent to tunnel blast and the semi empirical method, which is based on vibration measurement data, has been employed to consider blast vibration characteristics.

• Journal of the Korean GEO-environmental Society
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• v.12 no.11
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• pp.23-30
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• 2011

In this study, Terzaghi's formula was modified to solve problems considering the dilatancy effect of the soil for estimating the earth pressure acting on tunnel. It is performed for the comparison with Terzaghi's formula and modified Terzaghi's formula, tunnel model test result of Kobe University Rock Mechanics Laboratory. From comparison results of the earth pressure acting on tunnel, the earth pressure calculated by the Terzaghi's formula was estimated largest value. The earth pressure measured through the tunnel model test was least value. The difference between the earth pressure derived from Terzaghi's original formula and that derived from the modified formula was caused by the dilation effect, which was caused by the soil volume change. The difference between the earth pressure derived from the modified formula and the earth pressure measured through the tunnel model test, earth pressure results from the energy making failure surface. The results of FEM analysis were almost consistent with the results of mathematical analysis.