Abstract
The Lanzhou Yellow River Tunnel is the first metro shield tunnel that undercrosses the Yellow River in China. It was completed after successfully overcoming several construction challenges, including strata with a high proportion of large-sized sandy cobble stratum being saturated, large-scale sand pits along the bank of the Yellow River, and a combination of boulders and erratic blocks of rock. Given the difficulties in constructing the tunnel, this paper summarizes the scheme employed to transform the cutter and cutter head design to be applicable to sandy cobble stratum and the key technology used to form the slurry film to facilitate crossing the sand pits in a systematic way. The transformation scheme primarily involved the addition of an adjusting device to control the aperture ratio of the shield on the cutter head, a protective device for the hob hub, and a protective device for the piston rod in the oil cylinder of the crusher. The implementation of measures mentioned above guarantees the safe completion of the tunnel, which can provide a reference for similar projects.
Highlights
With the acceleration of urbanization, shield tunnelling methods have been widely applied to traverse various types of strata, facilitate rapid construction, and cause less interference to the surroundings
Yuan et al [5] and Ye [6] studied the influence of the slurry shield mud fluid properties on the stability of the excavation surface. e property indicators of slurry in sandy cobble stratum were determined based on experience and testing
By summarizing the measures adopted to address the problems in the process of the construction of Lanzhou Yellow River Tunnel, including the strata with a high proportion of large-sized sandy cobble stratum being saturated, large-scale sand pits along the bank of the Yellow River, and a combination of boulders and erratic blocks of rock, the following conclusions are listed: (1) e success of the shield type selection for the interval from Yingmen Beach to Ma Beach for the Lanzhou Metro is suitable for use as a reference in strata with a high content of large-sized sandy cobbles and water
Summary
With the acceleration of urbanization, shield tunnelling methods have been widely applied to traverse various types of strata, facilitate rapid construction, and cause less interference to the surroundings. E undercrossing of the Yellow River by Lanzhou Metro Line 1 is the first urban rail transit traffic tunnel along the Yellow River and is located in an area with a high content of large-sized sandy cobble stratum being saturated, which presented many technical challenges to the construction project. The sandy cobble strata in the riverbed of the Yellow River are characterized by a high cobble content, poor cementation, large permeability coefficient, and high water content, which make it more difficult for the Lanzhou Metro Tunnel to pass through. E paper presents a systematic analysis and summary of a series of problems that were encountered when the shield method was used to undercross the Yellow River for the Lanzhou Metro Tunnel with the intent to improve shield construction technology, to document our experience in sandy cobble stratum, and to provide a foundation for subsequent similar projects. The groundwater table on the tunnel site was higher than the tunnel roof in elevation; there was a risk of water surge in tunnel construction by the shield method
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