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Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objective The large section tunnel, due to flat shape and large span, usually adopts multiple steps and staged excavation. In the process of construction, the surrounding rock and the temporary support are repeatedly disturbed, affecting the stability of surrounding rock and supporting structure. Therefore, the deformation characteristics of the surrounding rock should be studied and the construction scheme should be optimized. Method Taking the mined tunnel of Qingdao Metro Line 4 in turn-back section as the example, based on the on-site monitoring data and using finite element simulation, the deformation characteristics of the surrounding rock in the excavation process of the large-section metro tunnel with three-step and nine-stage method are analyzed, and then compared with the optimized three-step and five-stage method. Result & Conclusion The simulation results show that the ground settlement is relatively large caused by the current construction scheme within the horizontal distance of 26m from the tunnel center line, accounting for 89.77% of the total settlement. The arch and the spandrel deform are large after excavation, and the maximum settlement reaches 102 mm. The stress of the surrounding rock of the arch increases rapidly with excavation. As the excavation advances, the local principal stress concentration appears in the upper part of the haunch and the corner. The optimized three-step and five-stage excavation method can realize rapid excavation and support, and simplify the construction process by 40%, while reducing disturbance to the surrounding rock and controlling its deformation within a reasonable range of 10 mm. Thus, the stress redistribution of the arch and the stress concentration in the corner are improved.

Copyright of Urban Mass Transit is the property of Urban Mass Transit Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The control of surrounding rock is a challenge faced during large-section tunnel construction, resulting in insufficient strength of the traditional support. Confined concrete arches with high strength and rigidity are suitable for controlling large-section tunnel surrounding rocks. To effectively control the soft surrounding rock of large cross-section tunnels, it is necessary to study the bearing characteristics and influencing mechanisms of confined concrete arches. A mechanical test on large-scale arch in traffic tunnels is conducted. The deformation mode and ultimate bearing capacity of the arch are analysed. The test results show that the deformation mode of the confined concrete arch is "the vault and bottom converge inwards, and the whole arch becomes flat". The maximum bearing capacity of the arch in the stable bearing stage is 830.7 kN, and the ultimate bearing capacity is 1157.2 kN. On the basis of laboratory tests, numerical simulations are conducted on different arch dimensions and cross-section parameters. The influence mechanisms of the section dimension and arch design parameters on the bearing capacity are clarified. As the section dimension increases, the load-bearing capacity of the arch decreases continuously. The ultimate bearing capacity of the arch with an on-site size is 784.5 kN, which is 32.2% lower than that of the arch in the laboratory test. A comprehensive evaluation index considering cost and bearing capacity has been established to select reasonable design parameters for confined concrete arches. Based on the above research results, engineering suggestions are put forwards, and the arch is applied in the Letuan tunnel, which effectively controls surrounding rocks. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to explor the influence of the inclination angle of wedge cut hole on the blasting effect of large-cross section tunnel, Bayueshan Tunnel of Tong’an Expressway was taken as the engineering background. Combined with the rock breaking theory of wedge cutting blasting, the rock mass parameters were obtained with the mechanical experiments, and the wedge cutting models with different inclination angles were established. The influence of wedge cut hole inclination angle on blasting effect was analyzed from three aspects: effective stress, surrounding rock dynamic damage and groove cavity evolution, the best cutting angle of the third grade surrounding rock was put forward. The results show that the effective stress of 60° hole arrangement is the highest, and the damage area of surrounding rock of 70 ° hole arrangement is slightly about 60 °, but the damage area of surrounding rock at the bottom of 60 ° hole arrangement is the most flat. The groove cavity with 60 °holes is the largest, with a maximum size of 2.18 m in horizontal direction and 1.68 m in vertical direction. The average utilization rate of blastholes in the field test is 86.74%, and the unit consumption of explosives is reduced by 0.02 kg/m³. To sum up, the optimal layout angle of cutting holes in grade III surrounding rock is 60°. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large section tunnels have huge excavation spans, complex excavation procedures, mutual influence among various procedures, multiple disturbances of the surrounding rock, and discontinuous connection among linings under different procedures, which bring great difficulties to their construction. The Caijianwei Mountain No. 2 tunnel of the Xiamen Haicang Evacuate-channel project in China belongs to a super large section tunnel. The tunnel’s maximum excavation section span reaches 30.52 m, and the excavation area reaches 421.73 m2. Its excavation sequence, the timing of the second primary lining support, temporary support disassembly, and secondary lining support of the double-side heading method were analyzed using numerical methods. The excavation sequence of the double side-heading method from the right pilot tunnel to the left pilot tunnel and then to the middle pilot tunnel can avoid a large horizontal displacement at the arch waist and control the deformation of the lining. The excavation sequence from the middle pilot tunnel to the two side pilot tunnels was conducive to the bearing performance of the concrete at the arch crown. The excavation sequence from the two side pilot tunnels to the middle pilot tunnel can better protect the concrete safety at the arch waist. The timing of the second primary lining support, temporary support removal, and secondary lining support have different effects on the deformation and stress of the surrounding rock and support structures. In the construction process, the timing of the second primary lining support, temporary support disassembly, and secondary lining support should be determined according to the actual deformation and stress of the site section. The research results can provide a reference for the construction design of the double-side heading method for large section tunnels.

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the engineering prototype of new Jinjishan Tunnel in Fuzhou 2nd ring road, the 1/30 downscale ground-lining model was fabricated. Then the earthquake-simulating tests were carried out on the shaking table apparatus to explore the seismic responses and seismic properties of large section mountain tunnel. The time-domain analyses on the test results show that the PHA (peak horizontal acceleration) amplification coefficients of ground increase non-linearly with elevation. The elevation effect of ground takes "S" form, which distinguishes itself from other regular ones. The PCP (peak contact pressure) oscillation coefficients at the sidewall and the arch of lining increase almost linearly with the seismic intensity, which implies that the sidewall and arch carry a majority of seismic loading under large ground motion excitation. The frequency-domain analyses on the test results show that the existence of large section tunnel changes the seismic property of original ground significantly. The 1st and 2nd dominant frequencies reflect the seismic properties of original ground and lining structure respectively, and both of them decrease gradually with the repeated excitations. Meanwhile the frequency components around the 2nd dominant frequency are augmented significantly when the seismic wave passing through the model from bottom to surface. [ABSTRACT FROM AUTHOR]

Highlights • The primary support system of the high-strength confined concrete arch is developed in large section tunnel. • The intelligent arch installation equipment and other matching devices are developed. • Mechanized construction technology of the fabricated confined concrete arch is put forward. • Mechanics mechanism of fabricated arch is studied in the mechanized installation process. • The field application of mechanized construction of fabricated arch for large section tunnel is conducted. Abstract There are many challenges in the construction of tunnels with large section, such as weak surrounding rock control, low efficiency of the artificial construction and poor safety. To solve these problems, a new mechanized construction technology of the fabricated arch is put forward. This technology includes fabricated confined concrete (CC) arches, intelligent arch installation equipment and corresponding matching devices. With Longding Tunnel in China as the engineering background, laboratory and numerical comparative experiments are conducted on CC arches. The results show that the strength of the CC arch is 2.05 times that of the traditional arch. At the same time, a numerical calculation is carried out on the mechanical mechanism of the fabricated CC arch during the mechanized construction. The results show that the stress on each cross-section of the arch decreases as the arch inclination angle increases and the largest stress is 101.2 MPa on the vault in the arch lifting. In order to avoid the arch damages during the installation, a reinforcement method is proposed to lift the key parts of the vault with splints. Based on the above research results, the mechanized construction of the fabricated arch is carried out at the site of Longding Tunnel. The construction efficiency is significantly improved and the deformation of the surrounding rock is effectively controlled. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The large section tunnel support is facing tremendous challenges. They are large in span and poor in self-stability of surrounding rocks. Traditional I-steel arches are easily subject to buckling failure. As a result, safety accidents always occur, such as the failure of supporting system and the collapse of tunnels. To solve the problems, a new support technology of confined concrete and corresponding arches are invented. With high strength and rigidity, it can effectively control the deformation of surrounding rocks on large section tunnels. To clarify the bearing capacity and failure mechanism of the new arch, a mechanical testing system for the combined arches in large section tunnels is developed. Comparative tests were carried out on the mechanical mechanism of the combined arches of confined concrete and traditional I-steel. The tests took Longding Tunnel, one of the largest city road tunnels in China, as engineering background. In the test, the following results were found. The in-plane flexural buckling occurred on the vault of the combined I-steel arch first, and then out-plane flexural-torsional buckling occurred on the hance and bottom of the arch. It resulted in the overall loss of its bearing capacity and the entire arch being flattened. In the other hand, the confined concrete combined arch showed no severe deformation; its bearing capacity was 2.63 times that of the I-steel arch; and its average rigidity at the coordinated bearing stage is 2.51 times that of the I-steel arch. It is superior in bearing capacity and stability to the I-steel arch. Based on the experimental research conclusions, the engineering suggestions are put forward for the application of the confined concrete support technology in tunnels and the field application was carried out. The control effect is excellent on surrounding rocks. The results can provide a reference for the future research and design in this field. [ABSTRACT FROM AUTHOR]