A comprehensive estimation of the probability and the degree of the possible injury or damage to health in a hazardous situation in order to select appropriate safety measures.

A process by which specific measures are devised and implemented to eliminate or reduce the level of risk.

A round steel bar, sometimes very long but usually less than 25 ft long, equipped with an expandable anchor at the far end, inserted in drilled holes around the periphery of a tunnel to tie rock-blocks or strata together and prevent their loosening or falling out. It may be locked into the hole mechanically or with some type or grout. It may be tensioned or untensioned.

A spontaneous and violent detachment of a slab or slabs from over-stressed rock. See also popping rock.

A 5- to 40-ft long steel reinforcing bar inserted in drilled holes around the periphery of a tunnel and anchored or sealed with mortar or polyester resin to tie rock-blocks or strata together and prevent their loosening or falling out.

The provision of larger stone or rock to prevent erosion or dredging

A modified core recovery percentage in which only sound pieces of rock core 4 in. or more in length are counted as recovery. RQD is considered a more accurate gauge of a rock's engineering "quality" or competence than is the gross recovery percentage. It is stated as the cumulative percent of the core run occuring in pieces greater than 4 in. long.

The distance broken rock will be thrown down the tunnel when the round is exploded.

A tunnel driven in consolidated natural material (i.e., "rock") which requires use of rock excavation methods such as blasting, channeling, wedging, or barring, or a tunnelling machine making use of specially hardened cutters.

A cutter consisting of a circular metal disk with hardened rim or teeth, mounted on bearings set in the rotating face of a TBM and rolled in an arc across the rock face under force; the resulting concentration of force or of stress spalls the rock. See also disc cutter.

The configuration of the upper portion of a tunnel section above the springline. The crown or back of a tunnel.

Bolts equipped with an expanded anchor at one end and a nut and washer at the other. Installed in drilled holes to tie rock together. Also known as rock bolts

Protection provided to the waterproofing membrane on the roof against accidental damage.

A cycle of rock excavation consisting of drilling blast holes, loading, firing, and then mucking.

A measurement of alignment that distinguishes between single tube and multiple tube configurations for the purpose of equating the utility of borehole surveys. For example, one borehole may be used to survey (theoretically) twice as many linear ft of tunnel for a double tube system as for a single tube system. Thus, one route ft in a double tube system comprises two linear ft of tunnel alignment; in a single tube system, route ft and linear are the same.

An operation of transporting and discharging unsuitable materials arising from the excavation, into a site previously selected for unsuitable materials.

Relatively sudden, uncontrolled flow of material into a tunnel from the face or the tunnel circumference.

Perfectly cohesionless materials (such as dry sand or clean, loose gravel) above the water table which flow into the excavated area while the tunnel is being excavated.