ROOF BOLTING

Series

Series Name

Mining Review 11th Year

Issue

Issue No.

3

Date Released

Nov 1957

Stories in this Issue:

1. 1TIN MINE
2. 2CRUNCH: Northumbria
3. 3ROOF BOLTING
4. 4MARKS MANAGER

Story

Story No. within this Issue

3 / 4

Summary

BFI synopsis: how this modern technique helps safety underground in mines.
NCB Commentary - Above ground the earth looks solid enough, but miners know better.
Underground the strata of different rocks are always on the move under the varying loads they receive.
This is the sort of thing that can happen when the strata get out of control.
Normal supports - steel arches and so on - may only last a few months before they give way under the enormous stresses they are expected to bear.
Let’s look at the problem in model form. Imagine that these strips of hardboard are the different strata underground; put a load on them and they’re free to slide one over the other. In fact, the layers may break or separate from each other.
Now, here’s a new way of tacking the problem.
Drill holes in the rock strata and bolt them together. Now see what happens. The strips act together as if they were a solid beam and they’ll take a load many times greater than they would when they work separately.
Where conditions are suitable, this technique is being used extensively in British mines today.
Here are some of the gadgets that do the job.
A roof bolt is made to expand at one end by being pulled down hydraulically inside a steel tube.
All this, of course, happens inside the rock, and the sleeve having expanded holds the bolt firmly in place.
Underground, the practical part of the job can be done by a two or four man team.
First of all, a hole is drilled the right length straight up into the rock strata. A thing like a giant vacuum cleaner sucks away the dust. When the hole has been drilled the bolt, with its tension tube and expansion cylinder, can be slipped into the bore hole.
Power to work the hydraulics comes from a hand-operated pump. As the cylinder is doing the work of expanding the sleeve to anchor the bolt into the rock, a gauge on the pump shows the load which is being put on the anchorage. For a three-quarter inch bolt like this, eight tons is just right.
Now the cylinder and tension tube are removed. A patch plate is put over the threaded end of the bolt. The nut to hold the patch plate in position is run up and then finally tightened by an electric wrench which applies just the right tension to avoid straining the bolt or anchorage.
The same technique can be used right at the coal face.
This face has got into such a bad shape that there’s a very real danger of it having to be shut down, but quick action, using the roof bolting technique, can still make it safe for work to carry on.
Once the roof has been brought under control, conventional methods of support can be used again.
Another big advantage of the roof bolting system is that it saves on material and on storage space, both above and below ground.
At the best of times steel arches are an awkward load to handle. Supplies for a shift’s work can be cut down to very manageable proportions.
Even taking into account the cost of the special tools that are needed, money and labour are being saved - and look at the difference in the space you have to move around.
Safety, ventilation, and overall efficiency can be increased by the use of this forward looking technique.

Researcher Comments

Commentary recorded 10th October 1957.

Keywords

Mining; Safety devices; Engineering

Written sources

British Film Institute Databases   Used for synopsis
The National Archives COAL 32   /12 Scripts for Mining Review, 1956-1960

Credits:

Production Co.

Documentary Technicians Alliance

Sponsor

National Coal Board