Traditional handwork and timbering will always have their place in locations that are small and difficult to access, and where there is little other choice of mining method. Wholesale use of handwork has been replaced with mechanisation and many of the backbreaking elements of handwork have been engineered out by the use of small plant. But the principles of handwork still remain, are still in use and demand a strong eye for detail.
My ten straightforward rules of thumb are far from exhaustive. Experience cannot be learnt, but only won:
¦ Rule 1 Study precedent. The starting point for any study of precedent has to be Colin Mackenzie’s excellent ‘Traditional timbering in soft ground tunnelling’ available as a free download on the British Tunnelling Society’s website (www. britishtunnelling.com).
¦ Rule 2 The principal risks of tunnelling all arise out of the forces of gravity and pressure. In handwork detailing, it is essential to make both forces work for the mining team rather than against it.
¦ Rule 3 Ground conditions. The engineer must be satisfied that the method suits the ground. If the ground is inadequate then ground treatment needs to be considered. Even with minimising the area of ground opened at any one time, some degree of stand-up is required and it is important to ensure the safety of both the miner and any overlying structures. Ground water must be dealt with – be ready for water whether it is expected or not.
¦ Rule 4 Plan. The timbering and support should be designed. Ground loading and imposed loading must be taken into account when designing structural members. Once designed, the system must be detailed to ensure buildability. Plan the work in detail before opening the ground; drawings and methods of working must be in place – detail even the cut size of timber. Make sure access and boarding can be manually handled into position. Build contingency into the method – what should happen in case of a loss of power?
¦ Rule 5 Mechanise wherever possible. All tasks need to be considered; only resort to muscle and brawn when all other forms of power have been ruled out. Mini conveyors are preferable to muck skips; small excavators are preferable to clay spades.
¦ Rule 6 In detailing the design and in executing the work, the collaboration between miner and engineer is essential. Always seek the advice of the experienced miner and take heed of his opinion.
¦ Rule 7 Always allow the ‘break-up’ to be away from the portal or main tunnel structure from where the works are being driven. Ground close to existing tunnel structures is often distressed and it is important to mine away from that distressed ground into fresh ground before breaking up.
¦ Rule 8 Progression of the work should be by opening up small areas of ground and providing adequate support before opening more. Never allow the ground to move, provide support before it moves. Always grout tight.
Detail the support so that the miner is able to work within the safety of the support system.
Always consider access, ensure that the miner and back-up workers are working on a safe access.
¦ Rule 9 In breaking up, work to the high point, break up to the roof and then work down. Once the roof is supported, structures can be mined downward allowing mined muck to fall into the lower section and be conveyed out.
¦ Rule 10 Monitor, monitor and monitor again, whether that be for surface settlement, convergence or handwork. Frequent inspection of the works can validate the detail and ensure works are being carried out on accordance with the design. Left to their own devices, miners tend to do what in their opinion is best for the job but may leave a fundamental detail out. Circumvent the inevitable arguments that arise in such situations by clear communication with the miner before the work is carried out. Follow by regular inspection of the work as it proceeds. Woe betide the engineer who neither inspects work regularly or builds a rapport with the miner, for he may go into the workings one day and find a ‘cathedral’ opened up in handwork as a testament to the miners’ use of their clay spades, yet without a splinter of timber being used to support it.
Monitor and record outputs and establish what has worked well and what has not worked so well…and learn from our mistakes.
SUMMARY
Do not let the ground know you are there.
Finally, the use of the term ‘square works’ is, I believe, a misnomer. There is little that is square in hand works other than in the timbering of shafts –so the term square work is best confined to the muck skip.
