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.

A mixture of cement, aggregate, and water projected pneumatically at high velocity from a nozzle onto a surface to produce a layer or layers of concrete. Shotcrete normally incorporates admixtures, especially accelerators, and may also include fibers. (also called Sprayed Concrete). (see dry-mix shotcrete, gunite, and wet-mix shotcrete)

The act of advancing a mole or shield with hydraulic jacks.

The process of advancing a subaqueous tunnel shield while its face is closed.

The pedestrian walkway at the side of a street (U.S. usage). Equivalent to pavement in U.K. usage

An extremely fine by-product of the manufacture of silicon metal as the gases escaping from the electric-arc furnace condense. It is used in concrete and shotcrete to improve their properties. In shotcrete its use reduces rebound increases thickness per pass, and improves properties of the hardened shotcrete.

A lung desease caused by breathing dust from rock drills over a long period of time. Rocks with high silica content are the most harmful.

Spelling in United States for Cill.

Crew of men located at one entrance to the tunnel who only excavate one heading at any one time for this entrance.

To excavate a shaft downwards from the surface, in distinction from raising.

Container used in hoisting muck from a shaft.

Rock cut through by finely parallel joints and/or cleavage planes so that it breaks into tabular plates upon exposure in an excavation.

The crumbling and disintegration of rock or hard soil upon exposure to air or water

The operation of enlarging a pilot shaft to full diameter by conventional methods.

Section of the discharge line from a concrete placer that is embedded in the fresh concrete during arch or full-circle pour.

The polished and sometimes striated surfaces on the walls of faults and shear zones, resulting from rubbing during earth movements. Sometimes referred to by construction people as "slicks".