China Unveils Hybrid Tunnelling System for Challenging Geology

China has introduced a novel tunnelling system, designated Xianglong, which reportedly combines boring and blasting capabilities. Developed by Tsinghua University and the China Railway Science & Industry Group, this 4.5 metre diameter machine integrates traditional tunnel boring methods with drill and blast techniques into a single unit. Laboratory testing conducted by Tsinghua indicates the new apparatus can achieve excavation rates 30 percent faster than conventional tunnel boring machines.

Credits: economictimes

The Xianglong machine was recently unveiled in Wuhan. This new tunnelling system is specifically engineered to address a range of acute challenges frequently encountered during the excavation of deep mountain tunnels. Such subterranean environments are known for their highly variable and often unstable geological compositions. Operators regularly contend with formations of soft rock that are susceptible to squeezing shut, abrupt and violent rock bursts, and sudden, significant inflows of water and mud, all of which pose substantial operational hazards.

Historically, project engineers have relied on distinct methods to overcome these subterranean difficulties, each possessing inherent limitations. The conventional drill and blast procedure, for example, proves effective in penetrating hard and heterogeneous rock formations. And while this method offers a degree of flexibility, it is widely recognised as both a protracted and inherently dangerous undertaking, involving the use of explosives and manual clearing.

Conversely, the tunnel boring machine, or TBM, offers rapid excavation rates under stable, predictable geological conditions. But these sophisticated mechanical borers typically struggle significantly when faced with abrupt transitions in ground composition, becoming inefficient or even stalled when the rock structure changes from hard to soft, or encounters unexpected water ingress. The developers at Tsinghua University and China Railway therefore aimed to integrate these disparate capabilities into a singular, more adaptable piece of machinery.

The technical mechanism underpinning the Xianglong's operation involves an innovative dual cutterhead configuration. This design features a hollow cutterhead positioned strategically alongside a central boring unit. This arrangement grants the machine distinct operational flexibility: it can initiate excavation by blasting first and subsequently boring, or alternatively, bore through material before deploying explosive charges. Critically, the system is designed to perform full-face boring without requiring any manual adjustments or swapping of components, streamlining the entire tunnelling process.

Embedded safety protocols are a key aspect of the Xianglong's design. This includes the integration of a robust explosion proof shield, specifically engineered to safeguard the machine's sensitive electronic systems. The shield offers protection against the concussive forces and debris generated during controlled blasting operations. According to Interesting Engineering, laboratory assessments conducted by Tsinghua University suggest this integrated operational approach facilitates excavation speeds reported to be 30 percent quicker than those of conventional tunnel boring machines.

With a diameter of 4.5 metres, the Xianglong is notably smaller than the average tunnel boring machine typically deployed on large infrastructure projects. This more compact size could allow its use in constricted environments or for projects where a smaller bore diameter is a specific requirement. So the machine's first operational deployment is scheduled for a pumped storage hydropower station. This demonstration project, located in Henan province, represents the initial phase of real-world performance validation.

During this initial deployment at the hydropower station, engineering teams are tasked with meticulously collecting comprehensive field data. This data acquisition process is considered essential for monitoring the Xianglong's performance across a range of operational scenarios. The information gathered will subsequently inform further refinements to the machine's design and operating procedures, aiming to optimise its efficiency and confirm its reported capabilities under actual working conditions. This ongoing evaluation forms a crucial step in the wider adoption of the dual-method technology.

• The Xianglong is a 4.5 metre diameter boring and blasting machine developed by Tsinghua University and China Railway Science & Industry Group.

• The machine integrates tunnel boring with drill and blast methods, offering operational flexibility for varied underground conditions.

• Laboratory tests indicate it achieves excavation rates 30 percent faster than conventional tunnel boring machines.

• Its initial deployment is at a pumped storage hydropower station in Henan for field data collection and performance validation.

Source: Interesting Engineering