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In addition to resource abundance, deep-sea mining benefits from high-grade deposits and lower operational costs compared to terrestrial mining due to reduced overburden removal. Optimizations such as reduced trench depth can cut mining time by 26% and increase deposit value by 53%. [147]
Tunnel Construction. Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management.
Excavation may be classified by type of material: [1]: 13.1 Topsoil excavation; Earth excavation; Rock excavation; Muck excavation – this usually contains excess water and unsuitable soil; Unclassified excavation – this is any combination of material types; Excavation may be classified by the purpose: [1]: 13.1, 13.2
Various geotechnical engineering methods can be used for ground improvement, including reinforcement geosynthetics such as geocells and geogrids, which disperse loads over a larger area, increasing the soil's load-bearing capacity. Through these methods, geotechnical engineers can reduce direct and long-term costs. [12]
Continuous trenching involves using a large cutting chain excavator system then using the trench box and hopper to continuously back-fill the trench with reactive media. Continuous trenching can be fast and thus, inexpensive, but can only be used for trenches less than 50 feet deep.
The risk of cave-in increases from surcharge load, which is any weight placed outside the trench near its edge. These loads include the spoil pile (soil excavated from the trench) or heavy equipment. These add extra stress to the walls of the trench. Inability to escape the trench because of steep and unstable walls, which may be difficult to ...
Cut and fill construction uses the spoils from cuts to fill in defiles to create straight routes at steady grades cost-effectively. Cuts are used as alternatives to indirect routes, embankments, or viaducts. They also have the advantage of comparatively lower noise pollution than elevated or at-grade solutions.
The trench is then carefully back-filled and the surface is reinstated. Top-down method: Side support walls and capping beams are constructed from ground level by such methods as slurry walling or contiguous bored piling. Only a shallow excavation is needed to construct the tunnel roof using precast beams or in situ concrete sitting on the walls.