• Geomechanics and Engineering
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• v.14 no.4
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• pp.367-376
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• 2018

Samples composed of coal and rock show different mechanical properties of the pure coal or rock mass. For the same coal seam with different surrounding rocks, the frequency and intensity of rock burst can be significantly different in. First, a method of measuring the strain variation of coal in the coal-rock combined sample was proposed. Second, laboratory tests have been conducted to investigate the influences of rock lithologies, combined forms and coal-rock height ratios on the deformation and failure characteristics of the coal section using this method. Third, a new bursting liability index named combined coal-rock impact energy speed index (CRIES) was proposed. This index considers not only the time effect of energy, but also the influence of surrounding rocks. At last, a new approach considering the influences of roof and/or floor was proposed to evaluate the impact capability of coal seam. Results show that the strength and elastic modulus of coal section increase significantly with the coal-rock height ratio decreasing. In addition, the values of bursting liability indexes of the same coal seam vary greatly when using the new approach. This study not only provides a new approach to measuring the strain of the coal section in coal-rock combined sample, but also improves the evaluation system for evaluating the impact capability of coal.

• Journal of the Korean GEO-environmental Society
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• v.23 no.8
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• pp.23-28
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• 2022

In Korea, 70% of the land is mountainous and structures occupy a high proportion in railway and road construction. In particular, in recent years, the construction of high-speed railways and highways for high-speed driving is rapidly increasing. At the same time, the construction of tunnels is also increasing. The number of tunnel construction cases in which long-term deformation occurs after tunnel excavation is completed is increasing. The stability of these tunnel structures depends entirely on the characteristics of the rock surrounding the tunnel excavation. In the case of pyroclastic rock, which is the subject of this study, it is generally vulnerable to weathering and has a characteristic that its strength decreases over a long period of time. Tunnel design and construction planning considering the strength characteristics of pyroclastic rocks are essential. This study analyzed the cases of over-deformation that occurred at the tunnel site in the pyroclastic section. Based on this study, a plan for tunnel design and construction management in an area where pyroclastic rock exist in the future is presented.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.595-609
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• 2017

Due to high in-situ stress and brittleness of rock mass, the surrounding rock masses of underground caverns are prone to appear splitting failure. In this paper, a kind of loading-unloading variable elastic modulus model has been initially proposed and developed based on energy dissipation principle, and the stress state of elements has been determined by a splitting failure criterion. Then the underground caverns of Dagangshan hydropower station is analyzed using the above model. For comparing with the monitoring results, the entire process of rock splitting failure has been achieved through monitoring the splitting failure on side walls of large-scale caverns in Dagangshan via borehole TV, micro-meter and deformation resistivity instrument. It shows that the maximum depth of splitting area in the downstream sidewall of the main power house is approximately 14 m, which is close to the numerical results, about 12.5 m based on the energy dissipation model. As monitoring result, the calculation indicates that the key point displacement of caverns decreases firstly with the distance from main powerhouse downstream side wall rising, and then increases, because this area gets close to the side wall of main transformer house and another smaller splitting zone formed here. Therefore it is concluded that the energy dissipation model can preferably present deformation and fracture zones in engineering, and be very useful for similar projects.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.205-217
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• 2007

The behavior characteristics of underground structures are reported as they are not affected by their dynamic characteristics such as surface structures, but by dynamic characteristics of soil and rock surrounding the underground structures. Therefore, dynamic behavior of surrounding soil and rock dominates the dynamic behavior of the underground structure. The purpose of this paper is to analyze the dynamic response (longitudinal deformation and ovaling deformation) of the underground structure under earthquake loading. The dynamic responses of the underground structures were evaluated with varying earthquake conditions, soil conditions, and structural conditions using conventional closed-form solution of seismic behavior of underground structure. In addition, shaking table tests were conducted to simulate the earthquake loading and the dynamic behavior of the model was analyzed.

• Earthquakes and Structures
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• v.26 no.5
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• pp.327-336
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• 2024

Evaluation of tunnel performance in seismic-prone areas demands efficient means of estimating performance at different hazard levels. The present study introduces an innovative push-over analysis approach which employs the standard earthquake spectrum to simulate the performance of a tunnel. The numerical simulation has taken into account the lining and surrounding rock to calculate the rock-tunnel interaction subjected to a static push-over displacement regime. Elastic perfectly plastic models for the lining and hardening strain rock medium were used to portray the development of plastic hinges, nonlinear deformation, and performance of the tunnel structure. Separately using a computational algorithm, the non-linear response spectrum was approximated from the average shear strain of the rock model. A NATM tunnel in Turkey was chosen for parametric study. A seismic performance curve and two performance thresholds are introduced that are based on the proposed nonlinear seismic static loading approach and the formation of plastic hinges. The tunnel model was also subjected to a harmonic excitation with a smooth response spectrum and different amplitudes in the fully-dynamic phase to assess the accuracy of the approach. The parametric study investigated the effects of the lining stiffness and capacity and soil stiffness on the seismic performance of the tunnel.

• Advances in concrete construction
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• v.11 no.5
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• pp.375-386
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• 2021

In this paper, a study of stability and health of a newly-built railway tunnel is presented. The field test was implemented to monitor the secondary lining due to the significant cracking behaviors influenced the stability and health of the tunnel structure. Surface strain gauges were installed for monitoring the status of crack openings, and the monitoring outputs demonstrated that the cracks were still in the developing stage. Additionally, adjacent tunnel and poor condition of surrounding rock were identified as the causes of the lining cracking by systematically characterizing the crack spatial distribution, tunnel site and surrounding rock conditions. Reconstruction of partial lining and reconstruction of the whole secondary lining were designed as the maintenance projects for different cracking regions based on the construction feasibility. For assessing the health conditions of the reinforced lining, embedded strain gauges were set up to continuously measure the strain and the internal force of the reconstructed structures. For the partially reconstructed lining, the outputs show the maximum tensile elongation is 0.018 mm during 227 days, which means the structure has no obvious deformation after maintenance. The one-year monitoring of full-section was implemented in the other two completely reconstructed cross-sections by embedded strain gauge. The outputs show the reconstructed secondary lining has undertaken the pressure of surrounding rock with the time passing. According to the calculated compressive and tensile safety factors, the completely reconstructed lining has been in reliable and safe condition during the past year after reinforcement. It can conclude that the aforementioned maintenance projects can effectively ensure the stability and health of this tunnel.

• Geomechanics and Engineering
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• v.35 no.4
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• pp.395-409
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• 2023

Long-span suspension bridges have tunnel anchor systems to maintain stable cables. More investigations are required to determine how closely tunnel excavation beneath the tunnel anchor impacts the stability of the tunnel anchor. In order to investigate the impact of the adjacent tunnel's excavation on the stability of the tunnel anchor, a large-span suspension bridge tunnel anchor is utilised as an example in a three-dimensional numerical simulation approach. In order to explore the deformation control mechanism, orthogonal tests are employed to pinpoint the major impacting elements. The construction of an advanced pipe shed, strengthening the primary support. Moreover, according to the findings the grouting reinforcement of the surrounding rock, have a significant control effect on the settlement of the tunnel vault and plug body. However, reducing the lag distance of the secondary lining does not have such big influence. The greatest way to control tunnel vault settling is to use the grout reinforcement, which increases the bearing capacity and strength of the surrounding rock. This greatly minimizes the size of the tunnel excavation disturbance area. Advanced pipe shed can not only increase the surrounding rock's bearing capacity at the pipe shed, but can also prevent the tunnel vault from connecting with the disturbance area at the bottom of the anchorage tunnel, reduce the range of shear failure area outside the anchorage tunnel, and have the best impact on the plug body's settlement control.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.1-17
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• 2024

Analyzing the tunnel excavation behavior and its effect on the surrounding ground involves large deformation behavior. Therefore, in order to properly simulate the tunnel excavation process and rigorously investigate the actual effect of excavation on surrounding ground and tunnel structure large deformation analysis method is required. In this study, two major numerical approaches capable of considering large deformations behavior were applied to investigate the effect of tunnel boring machine excavation on the surrounding ground: coupled Eulerian-Lagrangian (CEL) and the automatic remeshing (AR) method. Relative performance of both approaches was evaluated through the ground response due to TBM excavation. The ground response will be quantified by estimating the range of the excavation damaged zone (EDZ). By comparing the results, the range of the EDZ will be suggested on the vertical and horizontal direction along the TBM excavation surface. Based on the computed results, it was found that the size of EDZ around the excavation surface and the tendencies was in good agreement among the two approaches. Numerical results clearly show that the size of the EDZ around the tunnel tends to be larger for rock with higher RMR rating. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional due to higher confinement stress around the excavation surface.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.260-266
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• 2010

In this study, wish to analyze effect that affect on each tunnel (right and left tunnel) according as proceeding of leading tunnel (right tunnel), following tunnel (left tunnel) and pilot tunnel excavation through behavior of tunnel and surrounding base by model tests. And stress-transfer mechanism that occurs from in-situ loosing area and arching effect by difference of stiffness ratio and overburden heights were verified experimentally. The model tests were carried out by varying the stiffness of reinforced area and overburden height, measured deformation of tunnel and displacement of surrounding base. The model tests followed exactly the real 2-Arch tunnel construction stages.

• Geomechanics and Engineering
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• v.37 no.6
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• pp.555-563
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• 2024

The reasonable setting of coal pillar width plays a key role in guaranteeing the steadiness of surrounding rock of fully mechanized caving gateroad driving along the next goaf. Based on the engineering background of the Bayangaole mine, the discrete element method was used to simulate the fracture evolution of coal pillars with different pillar widths. The results show that the damage rate of the coal pillar increases with the decrease in the width of the coal pillar. Once the coal pillar width is smaller than 6 m, cracks run through the coal pillar, and the coal pillar is completely damaged. In the middle of the coal pillar, which has a width of 6 m and above, there is a relatively complete area with low damage. The results show that the pillar width of 6 m is the most appropriate. Field tests prove that the reserved width of a 6 m small coal pillar can effectively control the surrounding rock deformation, ensuring the overall steadiness of the gateroad in the thick coal seam. It is hoped that this study will offer some reference for the determination of the reasonable size of the coal pillar.