THE NEWCASTLE FORTIFICATIONS.
(BY OUR SPECIAL REPORTER.)
The Sydney Morning Herald
Tuesday 24 May 1881 Page 6 of 10
THE NEWCASTLE FORTIFICATIONS.
(BY OUR SPECIAL REPORTER.)
On Saturday last Colonel P. H. Scratchley, R.E., C.M.G., and Colonel C. F. Roberts, visited Newcastle for the purpose of inspecting the hill known as Signal Hill, near Nobby’s, upon which the fort recommended by Sir William Jervois and Colonel Scratchley is being constructed. Recently it was discovered that extensive coal-workings existed under the hill, and that it had been so much under-mined as to excite apprehension with respect to the security of the fortification works. The matter was reported to Colonel Scratchley by letter, dated the 14th ultimo, which he received about four days afterwards, and he then wrote to the Under-Secretary for Public Works, pointing out that it was necessary to obtain the opinion of an expert, and also of the Government Inspector of Collieries, as to the chance of any subsidence of the hill, and also as to the extent of the old coal workings.
Personally, from the information supplied, and considering the nature of the ground, he had no fear whatever that the works in progress would be effected, but it was desirable to have such opinions as those mentioned above, and also that a rough survey should be prepared showing the area occupied by the fort. Meantime the explosion of a blast used in connection with the excavating work carried on in the construction of the fort had either such an apparent or such a real effect upon a portion of the hill, in the way of loosening or shaking it, that the question arose whether it would not be wise to stop the work until something was done towards making the ground secure. Steps were immediately taken to ascertain as far as practicable the extent to which the hill had been under mined, and the course adopted was to reopen the old workings. These had been carried on in the old convict days all round the hill, and adits were found to have been made at every ten or twenty yards. As they were opened by removing the rubbish that filled them, it was seen that the passages into the hill were in most places very low, that they branched in various directions, and that, as far as could be ascertained, without knowing from actual inspection the extent of the workings, the hill was completely honeycombed. The condition of the headings and drives showed that the ordinary mining precaution of leaving pillars of sufficient strength to resist the pressure from above had not been followed. Instead of that, the pillars left as supports were very small and narrow, and the only object which appeared to have influenced those who directed the work of mining under the hill in years gone by was to get the coal out. This seems to have been done most completely.
The hill bears the reputation of having been the first place at Newcastle from which coal was obtained, and doubtless was the locality selected for the first coal-mining operations, because the out-crop of coal on the beach proved the existence of the mineral in the hill. Newcastle was a convict settlement in those days. Convicts worked in chains, with a file of soldiers in attendance; a formidable gaol, which has since rotted away, stood near the beach, not far from where the mines were opened ; and the taskmasters and gaolers were hard. Just where the fort is being constructed, a huge beacon was kept burning as a light to mariners – a practice that was continued until a lighthouse was built – and a large portion of the coal taken from the hill was used for this purpose. Six or seven feet of ashes were found by the workmen recently when engaged in excavating for the works connected with the fortifications. The circumstances that the hill was the first of the Newcastle coal-field to be discovered and worked, and that there was a large consumption of the coal obtained both for the beacon and for domestic purposes at the settlement, would necessarily cause the seam of coal that was found to be extensively opened out, and the hill to be pretty well exhausted of the mineral before the workings were abandoned. This is more likely to have been the case if the seams further inland had not been discovered at the time, or if, though one or more of them had been discovered, appliances were not at hand to work them: and it explains the present appearance of the hill.
As far as the passages that have been opened indicate, all the good coal that existed in the hill has been taken out. The seam was a very narrow one, not more than from eighteen to twenty-four inches, and as this good coal was taken out of the bill the space was filled in with rubbish which coal miners call “gob,” and which consists of inferior coal, mixed with the dirt which falls, from the roof and sides of a mine, and accumulates on the floor. So completely was the hill worked, that in some places not only are there the usual headings and boards, or passages running at right angles to one another, but extensive chambers, so low that one must almost creep to get along them, but so open as to leave a cavity under the hill which suggests very great insecurity unless proper precautions be adopted in the way of suitable supports to the roof. In all the passages timber was left by the convicts, but it was very small and in the lapse of years has in many instances become rotten and unsafe, and as the men who recently have been working with a view to ascertain the number and extent of the passages have met with this timber they have removed it and placed in its stead new props of good size and strength. But even this change has failed in one or two instances to keep the material overhead in its place, and by “creeping,” as the technical term for the subsidence of strata is, the roof has come down upon the supports and bent or split them most undeniably. This led Colonel Scratchley on Saturday to give directions that for the present no further passages should be opened out, as it was evident that taking out the rubbish and admitting the air into the interior of the hill had the effect of removing a support of more or less strength, and causing the material, of which the roof of the headings and boards were formed, to decompose and fall. In addition to the workings beneath the hill, there are one or two cracks or fissures on the surface, and near where the casemate battery is being constructed, which have ugly appearance, but it is believed that the portion of the hill where they exist can very well be dispensed with, and after it has been removed the face of the hill can be sloped, grassed, and made perfectly secure.
The main question to be considered is the course that should be taken with the underground workings. Concussion is the great element of danger, and this would, of course, be present in any active operations with the guns of the fort. Colonel Scratchley is decidedly of opinion that with proper precautions everything may be made as secure as if the hill were perfectly solid. He has decided not to stop the work of constructing the fort, not only because he considers there is no necessity for stopping the work, but also because this hill is absolutely the onlv site suitable for the fortifications. Anv other hill in the locality would be too far South for the purpose, and Nobby’s, the only site northwards, is too near to the entrance channel of the harbour, and is moreover more insecure than the hill where the fort is being built. Nothing could be better than the range of fire which the guns on Signal Hill will have, and as far is the fortification works have progressed they appear excellent in every way. How far the firing of the heavy guns will affect the underground workings is a matter that has yet to receive further attention. Considering the generial solidity of the hill, and the depth below the excavations for the fort, at which the coal workings have been carried on, Colonel Scratchley does not think the fortifications will be affected by the underground passages, but at the same time it is necessary to guard against all risks, and the point to be settled is one that cannot well be disposed of without consultation with a competent mining authority.
The contractor for the fortifications has been stopped from proceed ing further with the opening out of the underground workings, and a competent mining engineer, possessing not only a thorough knowledge of coal mining, but a perfect ac quaintance with the Newcastle district, will be called in to give his opinion with regard to the condition of the hill. Having done that, Colonel Scratchley will separate the work of constructing the fortifications from that of filling in or otherwise dealing with the underground passages, and have the latter done by contract in order to save unnecessary expense. His idea of the manner in which this work should be dealt with is probably the best that can be adopted, and it possesses the merit of being supported by the opinions of at least two independent authorties on the subject in Newcastle. He proposes that in a gradual and systematic manner the full extent of the workings shall be ascertained, that cross-walls of brick and cement 14 inches thick shall be built in the headings at every 15 or 20 feet, and then that the remaining spaces shall be filled with sand or other material, the mouths of the headings being closed with walls of sufficient thickness to completely exclude the air and so prevent any further disintegration of the shale which forms most of the roofs in the passages. All the timber props will be left as they are, to form additional supports to the roof. Getting this work done as far as possible by contract will of course considerably reduce the cost and it is believed that it can be done for, at the most, £2000. Colonel Scratchley will visit Newcastle again next Thursday, and will probably be accompanied by the Colonial Architect.
When the fort at Newcastle is completed it is expected that it will prove one of the most effective of its kind. The excavations for the guns, for the passages to and from the magazine, and for the shelter of the men, are in a very forward state, and as the concrete work progresses, it bears a very solid and finished appearance. Three 12-ton guns in barbette will command the approach to the port seawards, a casemate battery manned with three 80 pounders will defend the torpedo station and the submarine mines inside the harbour and an 80-pounder gun, also in barbette, near the casemate battery, will possess a range of fire from Nobby’s to the A A Co’s coal shoots.
The circumstance of so much dead weight on the hill as the presence of these guns will cause has been suggested as somewhat dangerous to the stability of the place, seeing that the ground has been so much undermined, but, though Colonel Scratchley does not attach much importance to this, he has decided not to have the roof of the casemate battery constructed until necessity for it arises, and this will relieve the top weight on one part of the hill considerably.
Transcribed by Doug Lithgow