Engineering Rock Mechanics

272 Rock reinforcement and rock support

working capacity of each bolt, T, is 150 kN, what area of the roof will

each bolt support?

(b) Would you anticipate any ancillary problems with this bolting

pattern?

(c) In the circular tunnel, in which directions and at which locations

would you install the bolts?

A16.5 (a) To find the area of roof p~ ___ -I+t ____
each rock bolt will support, we equate
the rockbolt load, 150 kN from A16.4,
to the support pressure times the roof
area required, A. Then 150 = 18.75A,
or A = 150/18.75 = 8 m2 of roof per @-----
rockbolt. If a square rockbolt pattern
is being used, there will be 2.8 m
between rockbolts, as illustrated to

upwards at the tunnel roof).

(b) The 2.8 m spacing between the bolts is sufficient to provide the

necessary strategic rock support, but the rock is only supported at the

heads of the rockbolts. This means that there are areas of exposed rock,

>2 m across, from which rock blocks can fall. The detachment of the small

blocks is avoided by using wire mesh that is attached to the bolt heads.

The picture below illustrates such a square rockbolting array with wire

mesh (although the bolt spacing shown here is less than 2.8 m).

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the fight (which is a sketch looking ___________ @ ___________ .@

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Rockbolt heads