Engineering Rock Mechanics

Questions and answers: excavation principles 261

Displacsments occur because

rock resistance

removed

EXCAVATION ROCK MASS

Effea 1: Displacements and rock failure

Intact rock

squeezed out

El& slides bnulbes

Out

Effect 2: Stress rotation

Effect 3 Water flow

EXCaV

as

Disdnlnuities

the stress concentrations around the excavation do not depend on the
excavation size: for example, caverns (in a given stress field and elastic
rock) with spans of 1 m, 10 m and 100 m (and having the same shape)
will all have the same stresses induced around them.

415.10 (a) Can drill and blast excavation rates be significantly

increased from those currently achieved?

(b) Can tunnel boring machine penetration rates be significantly

increased?

(c) Are new methods of excavation likely to be introduced?

A15.10 (a) Drill and blast excavation rates (using customary equip-
ment, methods and materials) are unlikely to be significantly increased,
because after decades of use the drill and blast technique has already
been optimized. Given the cyclical nature of the drill and blast process,
significant improvements are unlikely.
(b) In principle, TBM penetration rates can be significantly increased
because there is little difficulty in supplying large amounts of en-
ergy to these machines. The increased rates may occur, for example,