Abstract Considering that safe construction of the tunnel exit portal section is of great importance to the successful breakthrough of a unidirectional driven tunnel, and using the exit portal section of the Jinbang double-arch tunnel in Xiamen, which passes under a retaining wall, as an example, scheme optimization is conducted based on the geological and environmental conditions at the tunnel exit portal, and the deformation of the surrounding rock and retaining wall during construction are analyzed based on the measured data. The results show that: 1) after an optimized construction scheme (i.e., a 10-meter bored section on the side close to the mountain + a 27-meter bored section with roofing) was adopted instead of the original 37-meter open-cut construction scheme, the retaining wall and adjacent mountains were reserved, the impacts of construction noise and dust on the nearby residents were reduced, the construction period was shortened, and construction safety and environmental protection were ensured; 2) in addition to pollution reduction, the roofing of the 27-meter bored section also served as an extrados formwork of the secondary lining; 3) subjected to the convex retaining wall and adjacent mountains, the left tube has both the maximum convergence around the tunnel and the maximum vault settlement, and the convergence at the 27-meter bored section is relatively smaller with a value keeping within 15mm, which is attributed to the construction of two rows of ?159 steel pipe grouting piles on both sides; 4) the retaining wall and adjacent protected mountains would move in the direction of the free face without any external-force constraint, and this direction is the one in which construction disturbances occur.
Abstract：
Considering that safe construction of the tunnel exit portal section is of great importance to the successful breakthrough of a unidirectional driven tunnel, and using the exit portal section of the Jinbang double-arch tunnel in Xiamen, which passes under a retaining wall, as an example, scheme optimization is conducted based on the geological and environmental conditions at the tunnel exit portal, and the deformation of the surrounding rock and retaining wall during construction are analyzed based on the measured data. The results show that: 1) after an optimized construction scheme (i.e., a 10-meter bored section on the side close to the mountain + a 27-meter bored section with roofing) was adopted instead of the original 37-meter open-cut construction scheme, the retaining wall and adjacent mountains were reserved, the impacts of construction noise and dust on the nearby residents were reduced, the construction period was shortened, and construction safety and environmental protection were ensured; 2) in addition to pollution reduction, the roofing of the 27-meter bored section also served as an extrados formwork of the secondary lining; 3) subjected to the convex retaining wall and adjacent mountains, the left tube has both the maximum convergence around the tunnel and the maximum vault settlement, and the convergence at the 27-meter bored section is relatively smaller with a value keeping within 15mm, which is attributed to the construction of two rows of ?159 steel pipe grouting piles on both sides; 4) the retaining wall and adjacent protected mountains would move in the direction of the free face without any external-force constraint, and this direction is the one in which construction disturbances occur.
.Scheme Optimization and Monitoring Analysis for the Exit Portal Section of an Urban Double-Arch Tunnel under a Retaining Wall[J] MODERN TUNNELLING TECHNOLOGY, 2016,V53(3): 157-163
2016, Vol. 53 