A rock tunnel boring machine which generally utilizes roller disc cutters as excavation tools and which moves forward by reacting (i.e., exerting shove forces) against the tunnel walls through a hydraulic gripper reaction system.

Part of a ground support system consisting of a tendon inserted in a drilled hole, secured at the remote end, usually by means of a grouted plug, and tightened or tensioned against the ground retaining member in the system. Se also rock bolt.

The rock located immediately above a tunnel which transfers the overburden load onto rock located on both sides of the tunnel. The zone of arching is usually equal in height to 1.5 times the tunnel diameter. Overburden rock / ground above the ground-arch remains unaffected by the tunnel operations.

The application of processes which strengthen the soil, especially by filling pores and increasing shear strength.

Water contained in the ground below the upper level (the water table) of subsurface water.

A pumpable slurry of neat cement or a mixture of neat cement and fine sand, commonly forced into holes drilled from a tunnel to strenghthen incompetent soil/rock or to prevent groundwater from flowing into the excavation. See also chemical grout.

A foundation formed by filling the space between the underside of an element of an immersed tunnel and the pre-excavated trench bottom with grout. Until this operation is complete, elements require temporary support

Injection of grout through drilled holes, under pressure, to fill seams, fractures, or joints and thus seal off water inflows or consolidate fractures rock.

Original name for shotcrete (sprayed concrete) sometimes still (inappropriately) used for fine-aggregate dry-mix shotcrete.

A form of mortar consisting of fine sand, cement, and water which is sprayed on freshly excavated rock by air pressure to prevent deterioration of the rock, and in some instances to provide structural support.

Tunnel excavation by means of hand-helded tools rather than by heavy, mechanized cutting or digging equipment.

Massive rock containing no significant joints. When fractures by blasting, it breaks across sound rock.

In construction, rock having a strongly bonded nature such as to require excavation by blasting or the use of specially hardened cutters; generally includes igneous and metamorphic rock and the more strongly bonded sedimentary rocks.

Dangerous gases produced by engines.

A thickening of a wall or slab to increase locally the bending strength and shear capacity of the section.

A source of posible injury or damage to health

Tower built over a shaft to support the ropes for raising and lowering men, equipment, and material in the shaft.

The area at the front of the tunnel construction beyond the completed ring. Or a small tunnel constructed ahead of the main tunnel

A small advance tunnel driven for the purpose of enlarging to creat the main tunnel; similar to drift, but generally driven above the springline as a top heading.

The wall of unexcavated ground at the advance end of a tunnel. Similar in use to face