Milling machines are widely used in various construction fields, including tunnel and ditch excavation, municipal pipeline excavation, highway pavement breaking, mining, rock and frozen soil excavation, open-pit coal mine excavation, surface renovation, and the steel industry and forestry.
Specifically, the main applications of milling machines include tunnel and roadway excavation and contour correction (especially suitable for areas unsuitable for blasting), channel and trench milling, asphalt concrete and cement concrete pavement milling, rock and frozen soil milling, tree root milling, building demolition, open-pit coal mining, mine construction, slope restoration, pipeline trench excavation, foundation treatment, and sand and gravel mixing (longitudinal milling machines), etc.
(1) Application in Tunnel Excavation: In most cases, milling machines are only used for excavating the tunnel outline. However, in suitable strata such as medium- and low-hardness rock layers and frozen soil layers, milling machines can be directly used for tunnel excavation. Especially in fractured rock layers and old loess, the excavation volume can reach 30-60 m³/h, with low disturbance to the strata and high safety during the excavation process.
(2) Milling Machines: Milling machines are particularly suitable for sections where blasting is not feasible. They are easy to operate, highly controllable, and produce clear and accurate excavation outlines. They can easily solve problems such as under-excavation repair, internal surface grooving, and side ditch excavation within the tunnel.
(3) Excavation: On-site excavation is generally carried out in two steps, i.e., the two-step bench method. Since all equipment needs to be stored on the benches, the distance between the upper and lower benches is 800-1100 m. Step-by-step excavation and support: After excavation, steel mesh, steel grid + shotcrete are used to support the tunnel. In soft rock, the depth of each excavation depends on the condition of the rock strata at the tunnel face and the pre-design by the tunnel design unit, generally 50-80 cm.
(4) Excavation Cycle: After excavation using a milling machine, the excavator exits the tunnel face and stops against the tunnel sidewall. Then, the loader begins excavation. After excavation, the support structure is immediately installed and shotcrete is applied, followed by the next cycle of excavation.
(5) Problems encountered during excavation immediately after support completion: The excavation speed of a milling machine in clay (taking a TD140 milling machine with a 30-ton excavator as an example) is approximately 30-60 m³/h. When using a milling machine in clay layers, it is rare for the cutter head to become stuck in clay and unusable. This can be solved by washing the cutter head with water or by milling some dry, hard surrounding rock.
