Engineering Rock Mechanics

Questions and answers: rock reinforcement and rock support 267

of allowing the rock mass to deform in order to reduce the support loads.
It is not necessary nor possible to stop all rock displacements; indeed, the
rock may displace until it reaches a natural equilibrium position.
The questions in this chapter examine basic aspects of the rock stabil-
ization concept. There are questions on rock reinforcement, rock support
and an intermediate case. The questions in this chapter do not cover
specific rock engineering design (these are in Chapters 18 and 20), and
are intended to enhance understanding of the principles involved and
hence which stabilization strategy is liable to be optimal for a given
engineering objective and circumstances.

16.2 Questions and answers: rock reinforcement and

rock support

Ql6.l When rockbolts are used for surface or underground excav-
ations to reinforce a fractured rock mass, the rockbolts will be sub-
jected to tension, shear and compressive forces. The diagram below
(from Windsor,19972) indicates the types of forces on rockbolts a to f.
Recognizing that rockbolts are designed to operate in tension with
little shear force applied, rate these rockbolt configurations in terms
of their suitability on this criterion alone.

b

C

f

Al6. I The types of forces on the rockbolts are

a: tension and shear

d: shear and tension

b: tension only

e: shear only

c: tension and shear

f shear and compression

Rating these configurations in order from best to worst according to the
criterion 'tension with little shear force applied' gives: b, a and c, d, f, e.

Q16.2 A rock block of weight W is bolted to a plane inclined at angle
(11 to the horizontal. Develop an expression for the bolt tension, T, in

• Wmdsor C. R. (1997) Rock Reinforcement Systems. Int. J. Rock Meck Min. Sci. 34,
  919-951.