• Tunnel and Underground Space
• /
• v.20 no.5
• /
• pp.332-343
• /
• 2010

This study aims to evaluate the supporting effect of a spiral bolt that is superior to a rock bolt in terms of constructability, stability, environmental and economic aspects as a support system. This study thus analyzed the mechanical properties of a rock bolt which is widely used as a support and a spiral bolt. In addition, laboratory pull-out tests were conducted for the evaluation of properties of the supports such as displacement, pull-out load, confining pressure etc. Moreover, the differences between a rock bolt and a spiral bolt were drawn by comparing the two results of laboratory pull-out tests and in-situ pull-out tests. Then, the differences of the supporting effect of the two supports were analysed by comparing the results of the two pull-out tests with a numerical analysis using FLAC3D.

• Magazine of korean Tunnelling and Underground Space Association
• /
• v.10 no.4
• /
• pp.15-31
• /
• 2008

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.3
• /
• pp.201-214
• /
• 2013

Lattice girders are widely used as a substitute for H-steel ribs at domestic tunnels. However, lattice girders have a weak point in terms of the support capacity compare to H-steel ribs because of the lower stiffness and the weakness of the welded parts. To improve the weakness of the lattice girder, reformed lattice girders are developed in Korea by adding one more spider and having flat welded surface. Laboratory tests and field measurements were performed for the original and the reformed lattice girders to evaluate the performance of the reformed lattice girders. According to the laboratory compression test, reformed lattice girders have 16% higher load bearing capacity than that of original lattice girders. Reformed lattice girders are more stable than original lattice girders because reformed lattice girders tend to bend less according to the field measurements.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.1
• /
• pp.31-36
• /
• 2018

Recently, as the building construction works have been activated, the environment in which the excavation work is proceeding in parallel with the existing structure and the adjacent excavation work is increasing. However, there is not a lot of research on this. In this study, numerical analysis was carried out for interaction analysis between former excavation construction and follow-up excavation on two excavation retaining structures in parallel with excavation. As a result of numerical analysis, if the supporting load of strut is not considered, it was analyzed that the displacement distribution in the structure can be underestimated and acting stress of strut is overestimated. It was analyzed that the support stress causes by the former excavation should be considered in order to simulate the actual behavior characteristic.

• Tunnel and Underground Space
• /
• v.18 no.3
• /
• pp.226-238
• /
• 2008

The steel ribs which are used to enhance the supporting capability of the shotcrete are estimated to be very effective, but their characteristics depending on the types of steel support are not well understood enough to be considered in the design stage. This paper describes the behavior of the shotcrete reinforced by various types of steel supports. Through flexural toughness test, major strength parameters such as flexural tensile strength, equivalent flexural tensile strength and residual tensile strength were obtained and used in the numerical analyses. Test results show that steel rebar was not as dependable as H-beam or lattice girder but close examination of the test results revealed that the specimen was failed in shear because of the shorter span than desired. Therefore tests on the properly dimensioned specimens are necessary for valid evaluation of the steel rebar reinforced shotcrete. In the first set of numerical stability analyses, shotcrete and steel supports were modelled separately. Then compared with the second set of analyses in which shotcrete and steel supports were regarded as a composite material. The two results coincided reasonably and this equivalent model turned out to be useful.

• The Journal of Engineering Geology
• /
• v.30 no.3
• /
• pp.237-251
• /
• 2020

This study examined structural analysis of supports in tunnel and displacement and underground stress of tunnel by measurement, in order to evaluate the performance of high-strength lattice girders developed as a substitute for H-profiles. According to the three-dimensional nonlinear structural analysis results of the tunnel support, the load and displacement relationship between the H-profiles and the high-strength lattice girders showed almost the same behavior, and the maximum load of the high-strength lattice girders were 1.0 to 1.2 times greater than the H-profiles. By the results of the three-dimensional tunnel cross-section analysis of the supports, the axial force was occurred largely in the lower left and right sides of the tunnel, and showed a similar trend to the field test values. In the results of the measurement of the roof settlement and rod extension, the final displacement of the steel arch rib (H-profile) and high-strength lattice girder section in tunnel was converged to a constant value without significant difference within the first management standard of 23.5 mm. According to the results of underground displacement measurement, the final change amount of the two support sections showed a slight displacement change, but converged to a constant value within the first management standard of 10 mm. By the results of measurement of shotcrete stress and steel arch rib stress, the final change amount of the two support sections showed a slight stress change, but converged to a constant value within the first management standard of 81.1 kg/㎠ and 54.2 tonf.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.10
• /
• pp.17-25
• /
• 2012

Shotcrete, rockbolt, and steel rib are installed to support ground after tunnel was excavated. These are important supports for NATM applied tunnels. Recently, lattice girder is increasingly used because it is easily installed. In this study, we developed a new lattice girder by increasing contacting area between spider and rod. To verify the effect of the new lattice girder, the 3-point and 4-point flexural strength tests were carried out for LG-$50{\times}20{\times}30$, LG-$70{\times}20{\times}30$, LG-$95{\times}22{\times}32$. As a result, in case of contacting area, strength of new SGS lattice girder is 17.95% higher than that of original lattice girder. In case of weakness point, strength of new SGS lattice girder is 19.37% higher than that of original lattice girder.

• Land and Housing Review
• /
• v.2 no.2
• /
• pp.183-188
• /
• 2011

Recently, the depth of tunnel constructed is getting deeper, which increases difficulty in construction works. Deliberate tunneling techniques are needed as the span and length of tunnels are increased. As one of the technical developments for tunnel, U-shaped and reinforced spider lattice girders are developed by optimizing the spider used in 95mm lattice girder as tunnel steel ribs. In order to evaluate the load bearing capacity of the lattice girder, the 4-point flexural tests are carried out. For the laboratory tests, straight specimens are made for the existing lattice girder and the new lattice girder. The results of the flexural tests showed that the maximum load bearing capacity of the new lattice girders was higher than the traditional one. The load-displacement behavior of the test specimens showed the elasto-plastic behavior in the existing lattice girder and the stress softening behavior in the new lattice girder. It was found that the load bearing capacities are changed depending on the location of the loading points.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.3
• /
• pp.245-256
• /
• 2008

The steel rib, one of the main support of tunnel, plays a very important role to stabilize tunnel excavation surface until shotcrete or rockbolt starts to perform a supporting function. In general, a steel rib at the horizontal funnel is being installed in the direction of gravity which is known favorable in terms of constructability and stability. However, as the direction of principal stress at the inclined tunnel wall is different from that of gravity, the optimum direction of steel rib could be different from that at the horizontal tunnel. In this study, a numerical method was used to analyze the direction of force that would develope displacement at the inclined tunnel surface, and that direction could be the optimum direction of steel rib. The support efficiency of steel rib could be maximized when the steel rib was installed to resist the displacement of the tunnel. Three directions which were recommended for the inclined tunnels in the Korea Tunnel Design Standard were used for the numerical models of steel rib direction. In conclusion, the results show that all displacement angle of the models are almost perpendicular to the tunnel surface regardless of face angle. So if the steel rib would be installed perpendicular to the inclined tunnel surface, the support efficiency of steel rib could be maximized.

• Journal of the Korean Geotechnical Society
• /
• v.39 no.7
• /
• pp.31-37
• /
• 2023

Since tunnels are built underground, it is impossible to check visually the location and degree of deterioration of steel ribs. Therefore, in tunnel maintenance, GPR images are generally used to detect steel ribs. While research on GPR image analysis employing artificial neural networks has primarily focused on detecting underground pipes and road damage, there have been limited applications for analyzing tunnel GPR data, specifically for steel rib detection, both internationally and domestically. In this study, a one-step object detection algorithm called YOLO, based on a convolutional neural network, was utilized to automate the localization of steel ribs using GPR data. The performance of the algorithm is then analyzed. Two datasets were employed for the analysis. A dataset comprising 512 original images and another dataset consisting of 2,048 augmented images. The omission rate, which represents the ratio of undetected steel ribs to the total number of steel ribs, was 0.38% for the model using the augmented data, whereas the omission rate for the model using only the original data was 7.18%. Thus, from an automation standpoint, it is more practical to employ an augmented dataset.