Mumbai University > Civil Engineering > Sem 8 > Construction Engineering

Marks: 10Marks

The Popular methods are:

a) Full face method

b) Heading and bench method

c) Drift method

d) Cantilever car dump method

DRIFT METHOD:

Rock tunnelling is carried out first in smaller section of the proposed tunnel and then widened. This method is called as drift method. Drifts may be classified as:

Centre drift:

Main operations involved are:

The centre drift generally 3m x 3 m to 2.5 m x 2.5 m is first driven through portal to portal. Size should be sufficient to accommodate the tunnelling machinery, labour and mucking equipment.

Holes for enlargement are ring drilled with a drill set upon the axis of the tunnel. Rings are usually 1.2 m apart.

Side drift

Side drift is occasionally used in large tunnels in bad ground.Important operations involved are:

Two drifts are advanced along the sides of the tunnel,shown in figure . Breakups are then made into the arch and permanent timbering is erected to support the roof,which leaves centre core to be removed after tunnel is completely timbered

The core provides a working floor, for placing timbering. Temporary braces to hold the roof are set, before removing centre core, Sometimes concrete lining is placed before removing the core.

Top drift

When a smaller section,choosen for mining lies in the top it is known as top drift.

The drift section may be ABCDEF or BCEF.The size of the top heading is decided to suit the class of rock and equipment used. Portion 2 is drilled vertically downwards, loaded and mined under the lined roof.

Bottom drift

In this method, the lower part is first blasted and cleared for the full length.

i. The drift section may be ABCDEFGH or BCFG.

ii. The portion 2 is then drilled upwards and blasted down.

iii. Cross section of the bottom heading 1 should be such that muck from 2 provides enough room for drilling and scaling the roof.