Sinking: Wells and Shafts.
In 1881 the president of this section, Mr. Foster Brown, with Mr. Adams, read a paper before the Institution of Civil Engineers on “ Deep Mining of Coal in South Wales.”
In that paper the authors pointed out the great difficulty and expense attending the sinking of shafts through water-bearing strata and suggested that a boring might be put down in advance of the sinking, into which a pump might be placed to facilitate the operation of sinking. The water being pumped dewn in the boring below the bottom of the shaft the sinking would be done in dry ground and would go on without intermission.
The suggestion appeared to be a valuable one. In sinking shafts and wells through water-bearing strata on time honored methods there is not only the great cot but. what is often more serious, the great length of time taken in doing the work. A single well for town water supply often takes two or three years or more to execute.
The subject is of considerable local importance because of its bearing on the sinking of mining shafts, and it is on that account that I venture to bring it briefly before this meeting in Cardiff. The problem is simply that of keeping down the water in water-bearing strata in advance of the sinking operations, so that the excavation of the shaft or well shall be done in dry ground.
The ordinary method of shaft or well sinking is to sling a pump or pumps in the shaft and to lower the pumps from time to time as the sinking continues. Obviously the excavation has to be performed in water, and if the quantity of water to be dealt with is very great a large portion of the work has to be done by the men working in a depth of two feet or three feet of water. To facilitate the work and to reduce the water in which the men have to work, a sump is made under the suction pipe of the pump, shown in Fig. I, and it is the keeping this sump excavated in advance of the other work which is most difficult and tedious. Then there is the delay occasioned by the lowering of the pumps and providing the appliances necessary to the operation.
* A paper read before the British Association at Cardiff, by Henry Davey, M. I. C. E,
In the plan I now propose, the pump illustrated in Fig. 2 would be placed in a borehole made before the commencement of the sinking of the shaft. The only novelty in the pump is that of adapting it to the purpose. It is necessary that debris shall not go down the borehole in quantity sufficient to choke it up. That is provided against by means of a heavy taper shield of cast steel surrrounding the pump and resting on the edge of the borehole. The shield is perforated with holes inclined upwards towards the pump to allow water to get into the borehole, but to exclude debris. The shield is made very heavy and by its own weight follows the excavation around the pump and also protects it from injury through the blasting of the rock. The pump is made without a foot valve, the rod of the bucket working through the seating of a valve which rests on the top of the working barrel ; by this arrangement the drawing of the bucket also draws the valve ; and should the bottom of the borehole be filled up with sand it can be removed by lowering a scoop such as is used in making boreholes. The borehole should be made to a greater depth than that required for the pump to provide a space for sand and debris.
The application of this pump to the sinking of shafts would be varied to suit the local circumstances and the geological formation of the strata to be passed through. It would prolong the paper too much to go into all the details of various applications which might present themselves.
It is quite evident that in some situations the shaft might be drained by means of boreholes outside, as shown in pi in in Fig. 5, and this is a plan now being carried out in procuring water for town water supply.
It is the usual and necessary practice to provide duplicate pumping engines ; and where two engines are made to pump from the same well, the well must be very large that it may accommodate two sets of pumps, as in Fig. 4. Such wells are usually twelve feet to fourteen feet in diameter. To sink such a well in an ordinary way is a very long and costly undertaking, especially if quicksand is met with. On the completion of the well it may be necessary to drive adits to increase the water supply. A simple borehole is made very cheaply and very expeditiously—four thirty-inch boreholes can be put down in a very small fraction of the time required to sink a twelvefoot well in the ordinary way.
Instead of making a large well I put down four boreholes, as in Fig. 4, to accommodate the pumps to each engine. The boreholes being completed, the pumps are lowered into them and coupled up to the permanent engines. Immediately that is done the water found in the boreholes can be pumped and supplied to the town. Should it be insufficient then, a small well would be sunk in the dry to the bottom of the borehole pumps. The boreholes at the level of the pumps would be connected to the centre well and adits driven to collect more water. Should the boreholes yield sufficient water then there would be no necessity to sink the well.
Fig. 4 is the section of a completed well (shown in plan in F’g5). from which adits have been driven to collect additional water to that yielded by the boreholes. When such a well is made the changing of the working parts of the pumps may be done underground, thus obviating the necessity of drawing the pump rods from the top.
It would be absurd to advocate any particular system of well sinking as being universally applicable and expedient. My only excuse for bringing this paper before the section is that this system of making we♂lls and shafts certainly promises advantages under ordinary conditions, but the advisability of its adoption in any particular case must be a matter of judgment with the engineer planning the work. It may be of interest to the section to know that the practice of “dowsing** for finding water is not extinct in the West of England. There is a professional dowser in a county not far off and this man, for a sufficient inducement in the shape of the coin of the realm will, by means of a hazel twig, profess to find water. Holding the twig in his hand he will walk over the ground and coming to a place where water is to be found the hazel twig is said to turn down and give the indication that water will be found there.
The dowser has a considerable clientele among people said to be educated, but possibly not among members of the British Association.