The removal of loose pieces of rock adhering to the solid tunnel surface after blasting.

A slip form on an invert pour; anything used to strike off a concrete pour.

Following trench excavation and before immersing an element, a gravel foundation is prepared by screeding to close tolerances and onto which elements are placed directly without further adjustment. Temporary supports at bed level are not required.

The equipment required to be installed on diesel engines, whose purpose is to dissolve or neutralize exhaust gases.

A method of constructing a concrete wall in poor ground by means of a continuous row of concrete-filled boreholes. Alternate holes are bored in two successive series such that adjacent piles overlap.

A permanent tunnel lining of concrete that is usually placed after mining operations have been completed.

A condition safe from unwanted intrusion

A monolithic section of a tunnel element only separated from other segments by vertical joints. For concrete tunnels, a segment is typically the length of a single concrete placing operation. Some tunnel elements, particularly in the Netherlands, consist of a number of discrete segments held rigidly together during installation by temporary prestress and joined by expansion joints.

Sections of iron, steel, or precast concrete which can be bolted or keyed together to make up a ring of support or lining. Iron or steel segments are generally referred to as "liner plates"; concrete segments may be referred to as "panels".

See division of communities

One steel rib or unit of timber framing to support the sides and roof of a tunnel.

A pipe or conduit for transporting liquid waste for treatment or disposal

The network of sewers for a community

A vertical or near-vertical excavation or opening to provide access to an underground facility or construction operation

A device to transfer shear across a joint. Shear dowels are sometimes used in concrete tunnel elements across immersion, closure or expansion joints to provide continuity of alignment. Such shear dowels must permit relative longitudinal movement. For immersion and closure joints, the dowels would be embedded in cast-in-place concrete at the joint face after immersion.

A device to transfer shear across a joint, usually a moveable immersion joint. In concrete tunnels, the shear key components may form integral parts of the structure of each element. The keys are usually placed in the space between the end bulkheads adjacent to the immersion gaskets so that they can be inspected and repaired if necessary.

A local geologic structure resulting from the relief of earth stresses by he formation of a multitude of minute, closely spaced fractures with slight slipping or faulting along each.

A movable steel tube, framework, or canopy shaped to fit the excavation line of a tunnel and used to provide immediate support for the tunnel and protect the men excavating and providing the long-term support. May be fitted with a cutting device for excavating the tunnel lining. See also soft-ground shield and gripper shield.

An extension to the rear of the shield skin which supports soft ground enabling the tunnel primary lining to be rected within its protection.

Foreman of heading crew.