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Dewatering
The removal of water from granular soils, it is normally carried out within an impermeable cut-off wall and by using well points.

Diaphragm walls
A concrete retaining wall (usually reinforced) which is constructed in panels from the ground surface. Excavation for panels is undertaken by a long-arm excavator, with the ground supported by bentonite mud or similar. Once the reinforcement cage has been lowered into place, concrete is poured into the slot, displacing the mud. Once all panels have been cast, excavation of the ground within may proceed.

Double shield
A tunnel boring machine that is formed of two sections, each being capable of independent forward movement, this allows concurrent excavation and building of a tunnel lining.

Dowel bar/Shear dowel
Reinforcement which crosses a zone of shear, limiting movement.

Drill and blast
The excavation of a tunnel, shaft or cavern in rock using explosive charges placed in holes drilled in the face.

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