Numerical calculation of mechanical characteristics during construction of nine chambers in a 300 m2 class 5-lane tunnel
This paper investigates the construction technology and structural stress of a 300 m2, 5-lanesuper-large section tunnel involved in the Baopeng large underground interchange on Qiaocheng East Road in Shenzhen. Firstly, a construction technique for excavating nine chambers in a super-large sec-tion tunnel is proposed, involving sub-chamber excavation+reinforced lining support. Subsequently, utilizing tunnel geometry and support schemes, a three-dimensional finite element numerical calcula-tion model is established in Midas to explore the dynamic mechanical response characteristics of the ex-cavation construction for the 5-lane super-large section tunnel. Finally, stress cloud maps for each sub-section structure of the tunnel are extracted, and statistical analysis is conducted on the stress and dis-placement monitoring curves of characteristic measurement points. The research results indicate the need for advanced measures, such as small conduits and grouting within the pipe shed, to pre-reinforce the surrounding rock during the construction period. On site, a nine-chamber excavation method involv-ing double-sided wall guide pits and double temporary horizontal braces is required. Additionally, a sup-port scheme comprising double-layer initial support+reinforced thickened secondary lining support is ad-opted. After on-site excavation and construction, structural stress and displacement exhibit a rapid in-creasing trend, followed by the continuous forward movement of the tunnel face, eventually leading to the stabilization of the curves. The surrounding rock's peak pressure can reach 2.01 MPa. At the arch crown position, the maximum internal force of the leading small conduit is 10 kN, the maximum internal force of the pipe shed at the two sides of the arch waist position is 20 kN, the maximum internal force of the steel arch frame at the arch waist and arch foot positions is 113 kN, and the internal force of the lock-ing anchor rod at the arch shoulder position reaches 18 kN in the 66th excavation construction step. The peak stress at the measuring point of the initial support structure is 2.4 MPa, and the settlement peak val-ues at the initial support arch crown and arch shoulder are 12.4 mm and 6.8 mm, respectively. The com-bined support effect of the pipe shed, locking anchor rod, and other structures is significant.
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