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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%. [138]
Excavation is done using a special clamshell-shaped digger or a hydromill trench cutter, suspended from a crane. The excavator digs down to design depth (or bedrock) for the first wall segment. The excavator is then lifted and moved along the trench guide walls to continue the trench with successive cuts as needed.
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 ...
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
[18]: 5 There is an observed declined in groundwater storage in many parts of the world. This is due to more groundwater being used for irrigation activities in agriculture, particularly in drylands. [19]: 1091 Some of this increase in irrigation can be due to water scarcity issues made worse by effects of climate change on the water cycle.
As a tunnel or excavation progresses the roof and side walls need to be supported to stop the rock falling into the excavation. The philosophy and methods for rock support vary widely but typical rock support systems can include: Rock bolts or rock dowels; Shotcrete; Ribs or mining arches and lagging; Cable bolts; In-situ concrete
One of the earliest and most critical tasks in a submarine pipeline planning exercise is the route selection. [5] This selection has to consider a variety of issues, some of a political nature, but most others dealing with geohazards, physical factors along the prospective route, and other uses of the seabed in the area considered.