Shield Machines and Tunnel Boring Machines (TBMs) are large-scale machinery used in tunnel construction. While they share some similarities, there are key differences between them.
TBMs are generally divided into two main types: open-type tunnel boring machines and shielded tunnel boring machines. On the other hand, Shield Machines can be classified into various types, including hand-dug shield machines, compressed shield machines, semi-mechanical shield machines, mechanical shield machines (which include open-face cutting shields and compressed shields), slurry shield machines, earth pressure balance shields, hybrid shields, and special-shaped shields.
TBMs are typically used for hard rock excavation, often employed in mountain tunnels or large water diversion projects. Shield Machines, designed for soft ground excavation, are primarily used in urban subway construction and smaller pipeline projects. The structural differences are notable: TBMs are modern support-based machines with their structure consisting of excavation, support, and drive components, as well as transportation and assembly equipment. The support function of a Shield Machine’s excavation face is provided by the soil's cohesion and the resistance within the mesh's thickness range. As the Shield Machine advances, the soil is extruded through the mesh, and the mesh's opening area is adjusted based on the soil properties.
Differences Between TBM and Shield Machine:
1: Geological Conditions:
- Shield Machine: Primarily used in soft ground conditions, such as silt, new soil, and gravel layers.
- TBM: Designed for rock formations, especially hard rock, in tunnel construction.
2: Structure and Working Principle:
- Shield Machine: Aims to stabilize the excavation face using the shield method, achieving excavation, muck removal, and support construction (lining the tunnel).
- TBM: Generally employs an open-type excavation, with different cutting tools, muck removal equipment, and propulsion principles.
3: Construction Efficiency:
- Shield Machine: Suitable for weak ground, with a slower construction speed but minimal impact on the surrounding environment. The monthly progress is typically 200-300 meters.
- TBM: Excavates faster in hard rock, with higher efficiency, making it suitable for long-distance and large-section tunnel construction. The monthly progress can reach 600-700 meters.
4: Environmental Impact:
- Shield Machine: Has minimal impact on surface structures and traffic during construction, making it ideal for urban subway projects.
- TBM: Due to its high-efficiency rock-breaking capabilities, it reduces environmental disruption, making it suitable for long-distance mountain tunnels.
In summary, TBM is a broader concept, and a Shield Machine is a type of TBM specifically designed for soft ground and water-bearing strata. Both play essential roles in tunnel construction.