China’s largest domestic TBM ready for Hefei reservoir drive

A 16.68m diameter slurry TBM has completed factory acceptance ahead of a 2.9km drive beneath Dongpu Reservoir in Hefei, China. Named China Railway 1662, the machine completed factory acceptance in Zhengzhou on September 15 and will be deployed on Lot 1 of the Hefei G4001 Link, also known as the North Second Ring Road West Extension.
The TBM was developed and manufactured by China Railway Engineering Equipment Group (CREG) in collaboration with Lot 1 contractors China Railway Tunnel Group and China Railway No.4 Engineering Group. The RMB3.17bn (US$445m) Lot 1 contract has a construction period of 1,460 days.
The wider North Second Ring Road West Extension crosses Hefei’s Shushan and Luyang districts and extends approximately 10.6km from the North Second Ring interchange to the Bailianyan Road expressway interchange.
Lot 1 runs approximately 3.8km from the West Second Ring Road/Qingxi Road interchange to Kexuedao Road and will provide eight traffic lanes. Its principal tunnelling element is a 2.9km shield-bored crossing beneath Dongpu Reservoir, constructed as twin, double-deck tubes.
The reservoir provides both flood-control and drinking-water functions, making the crossing an unusually sensitive application for a super-large diameter TBM.
China Railway 1662 has an excavation diameter of 16.68m, an overall length of 125m and weighs approximately 4,800t. Its accessible cutterhead system is designed to allow cutter replacement at atmospheric pressure with chamber pressures of up to 8bar, avoiding the need for hyperbaric cutter interventions.
The alignment presents a series of demanding tunnelling conditions, with the TBM required to pass close to the West Second Ring elevated highway and the reservoir dam, as well as beneath a protected drinking-water area.
The machine also has to negotiate steep gradients and tight-radius curves. Its thrust system incorporates hydraulic floating supports, together with high-precision guidance and segment-selection systems designed to maintain alignment and reduce loading on the thrust cylinders and segments when negotiating curves down to approximately 600m radius.
The TBM is fitted with a 38% opening-ratio accessible composite cutterhead and a dedicated muck-removal system. Excavated material is discharged by screw conveyor before being crushed outside the excavation chamber, allowing crusher maintenance to be carried out without personnel entering the pressurised chamber.
Construction of the reservoir crossing is already under way, with excavation of the TBM launch shaft and construction of the working-shaft base slab previously completed.
The project is one of a relatively small number in China to combine a super-large diameter shield-bored crossing beneath a major water-supply reservoir with a twin-tube, double-deck highway tunnel configuration.
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Facts Only

* A 16.68m diameter slurry TBM completed factory acceptance ahead of the drive beneath Dongpu Reservoir in Hefei, China.
* The machine, named China Railway 1662, achieved factory acceptance in Zhengzhou on September 15.
* The TBM will be deployed on Lot 1 of the Hefei G4001 Link, also known as the North Second Ring Road West Extension.
* The TBM was developed by China Railway Engineering Equipment Group (CREG) with contractors China Railway Tunnel Group and China Railway No.4 Engineering Group.
* The Lot 1 contract is valued at RMB3.17 billion (US$445m) with a construction period of 1,460 days.
* The wider road extension crosses Hefei’s Shushan and Luyang districts over approximately 10.6km.
* Lot 1 tunnels approximately 3.8km from the West Second Ring Road/Qingxi Road interchange to Kexuedao Road, providing eight traffic lanes.
* The principal tunneling element is a 2.9km shield-bored crossing beneath Dongpu Reservoir, constructed as twin, double-deck tubes.
* The TBM has an excavation diameter of 16.68m and an overall length of 125m, weighing approximately 4,800t.
* The cutterhead system allows cutter replacement at atmospheric pressure with chamber pressures up to 8bar.
* Excavated material is discharged by a screw conveyor before crushing outside the chamber.

Executive Summary

A 16.68m diameter slurry Tunnel Boring Machine (TBM), named China Railway 1662, completed factory acceptance in Zhengzhou on September 15. The TBM will be deployed on Lot 1 of the Hefei G4001 Link, known as the North Second Ring Road West Extension. The TBM was developed by China Railway Engineering Equipment Group (CREG) in collaboration with the China Railway Tunnel Group and China Railway No.4 Engineering Group. This Lot 1 contract is valued at RMB3.17 billion (US$445 million) and has a construction period of 1,460 days. The project involves tunneling beneath Dongpu Reservoir, which serves flood-control and drinking-water functions, making the crossing highly sensitive. The route extends approximately 10.6km across Hefei’s Shushan and Luyang districts. Lot 1 specifically runs about 3.8km between the West Second Ring Road/Qingxi Road interchange and Kexuedao Road, accommodating eight traffic lanes. The central tunneling element is a 2.9km shield-bored crossing beneath the reservoir, constructed as twin, double-deck tubes. The TBM has an excavation diameter of 16.68m and is designed for cutter replacement at atmospheric pressure up to 8bar.

Full Take

The project highlights a convergence of extreme engineering requirements—super-large diameter tunneling under critical water infrastructure while navigating complex environmental and topographic constraints. The TBM's design, specifically its ability to operate at atmospheric pressure for cutter replacement and handle tight-radius curves with hydraulic floating supports, addresses the inherent conflict between massive construction needs and sensitive constraints like the reservoir. The complexity lies in integrating this super-large crossing beneath a vital water source, which simultaneously requires flood control capacity and potable water security, positioning the TBM application as unusually sensitive. The pattern emerging is the scaling of infrastructure projects to meet high-stakes functional requirements; here, the engineering solution must balance efficiency (large diameter/high volume) with extreme constraint management (water safety, tight curves). The fact that the excavation methodology allows for external crushing and non-hyperbaric cutter maintenance suggests a focus on operationalizing safety within a high-pressure environment. The central implication is how large-scale infrastructure development necessitates novel mechanical solutions capable of managing simultaneous, often contradictory, demands—such as maximizing capacity while minimizing impact on sensitive environmental systems. What assumptions underlie the prioritization of this specific TBM configuration for this specific application over alternative tunneling methods that might exist? How does this highly specialized engineering precedent set a standard for future large-scale infrastructure crossings beneath water bodies?

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