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| The stability of structure and its control technology for lager-span loess tunnel |
| CHEN Jianxun, LUO Yanbin
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| The stability of structure and its control technology forlager-span loess tunnelCHEN Jianxun, LUO Yanbin(Key Laboratory for Bridge and Tunnel of Shaanxi Province, School of Highway Engineering, Changan University, Xian 710064, Shaanxi, China |
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Abstract During the construction of large-span loess tunnel, surface cracking, settlement deformation, support invasion and landslides are easy to occur, which makes the construction of large-span loess tunnel extremely difficult. Based on the pier-beam tunnel, the largest-span highway loess tunnel excavated in the world at present, the combination of field measurement, theoretical analysis and numerical simulation was used to analyze the deformation law of large-span loess highway tunnel. Combined with the relevant research results and engineering practice experience of support design of single loess tunnel and two-lane loess tunnel, the structure type of the initial support was put forward, and structural force and stability of initial support were studied. The results showed that the convergence at the upper step and the maximum excavation line could be divided into four stages when the three-step method was adopted. The convergence rate at the upper step was faster than that at the maximum excavation line, and the final convergence value at the maximum excavation line was about three times of that at the upper step. As the distance between the settlement curve and the face increases, the settlement value increased continuously and the growth rate slowed down. Within the range of 1D, 1D to 2D, 2D to 3D and 3D to 4D from the palm surface, the settlement values generated by each measuring point were 49%, 23%, 12% and 6% of the maximum settlement values, respectively. The large-span loess tunnel colud ensure the stability of the tunnel structure by adopting the composite structure of “steel frame+shotcrete+steel mesh+anchor bolt(pipe)+longitudinal connection bar”. The double-sided guide pit method was adopted in the construction of the tunnel entrance section, the three-step retaining core soil method in the construction of the tunnel body section, and the stability control technology of the large-span loess tunnel strengthened by steel pipe grouting was adopted in the tunnel bottom with low bearing capacity in the shallow section.
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Received: 27 November 2018
Published: 22 February 2019
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