Clause in the specifications that relieves the contractor of financial responsibility for certain events not under his control. Examples include acts of God, war, earthquakes, floods, and strikes

A ground improvement measure carried out by inserting bars, rods or tubes at the face so as to form a splayed arch ahead of the tunnel. It can involve areas of jet grouting or ground freezing. Previously, the term was used more narrowly. It related to polling boards driven on a splay ahead of the face of an excavation.

Traveling frame used to strip, collapse, and erect full-circle or arch forms.

Tunnel linings of performed metal or concrete

Timber or metal surfaces which retain wet concrete to form desired shape

Air at atmospheric pressure.

The height above the still-water surface of the highest part of a floating body.

A 3- to 8-ft long steel bar with a slot along its entire length, inserted in drilled holes of slightly smaller diameter around the periphery of a tunnel. The slot causes the stabilizer to be in compression and exert an outward anchoring force to tie rock-blocks or strata together and prevent their loosening or falling out.

Tunnel excavation to full cross-sectional size with each blast or shove. Distinguished from heading, bench, and multiple drift.

Process in which the complete concrete lining in a tunnel is poured in one operation. See Arch pour, Invert pour.

An excavation of the whole face in one operation.

Smoke produced in the construction site.

Walls or surfaces placed inside the structural walls of a tunnel or cavern. Furred out walls are usually for aesthetics purposes or to provide a space for water seepage and collection.

One of a number of tunnels driven sequentially and in parallel. They are progressively connected one with another to form a single tunnel of larger cross-section. May also be called drifts

Drill jumbo which has an open space in the center large enough for muckers, cars, and locomotives to pass through the jumbo; supported by separate rails, tracks, or tires.

A device that acts as a seal between two contacting surfaces.

(5) Temporary Immersion Gasket: This is usually an extruded rubber section that acts as a seal when it is compressed. After completion of the permanent joint, the seal is no longer needed. This type of gasket is commonly used in the United States.

(4) Soft-nosed Gasket: See Gina Gasket, above.

(3) Omega Gasket or Seal: This seal, shaped like the Greek letter Omega (W) is installed across flexible immersion joints from within a tunnel after immersion and joining. It may form a secondary permanent seal or it may become the primary seal. It is bolted to the internal faces each side of the joint. It may be replaced in a similar manner on an as-needed basis. Because of its shape, it can sustain fairly large longitudinal and transverse movements at the joint.

(2) Gina Gasket: A proprietary form of gasket used to seal immersion joints, particularly on concrete tunnels. It consists of a full-bodied rubber section able to transfer large compression forces, and a soft nose able to provide an initial seal under low compression. For binocular sections, each circular tunnel usually has its own gasket around the perimeter, whereas most other forms of tunnel use a single gasket around the external perimeter. The gasket provides a temporary seal and compression contact face during immersion installation, remains in place, and may provide a permanent seal at flexible joints.