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Backfill
A material used to replace excavated soil.

Bench
It is in situ ground at the lower face of a tunnel undergoing staged excavation.

Bentonite
Bentonite is clay composed, like fuller’s earth, mainly of the same clay mineral ‘montmorillonite’. It is used for synthetic reasons, expanding properties when water content increases.

Bolt pocket
A pre-formed recess in tunnel segment to accommodate bolts which hold segments together.

Bore
The internal diameter of a pipe or other cylinder, single tunnel e.g. Twin Bore.

Borehole
A hole driven into the ground to get information about the strata, or to release water pressure by vertical sand drains, or to obtain water, oil, gas, salt etc.

boringBoring/bored
Making a hole in the ground by means of
a rotating auger.


Box Jack/Jacked box
A fully built structure that is constructed and then thrust into final position from an adjacent jacking point.

Burden (blasting)
The burden of the toe of a blasting hole is its distance from the nearest free face measured at right angle to the hole.

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