« PreviousContinue »
Archway Road, made with a foundation composed of Roman cement and gravel.
This road, of little more than a mile and a
broken stones, and the retentive soil below. Any water which may percolate through the surface, is received amongst the stones of the pavement, and runs from them into the next leading, or cross drain, and there escapes. Was there no pavement, the water must remain among the working materials of the road, or rest on the surface of the clay till again evaporated. Should frost succeed, the pavement prevents its acting on the clay, as the water has previously escaped; and as hard stone is not perceptibly altered by frost, it consequently can produce no effect on the surface. Where the water cannot escape, or when, from a want of the intermediate pavement, the frost reaches the clay, which always contains a considerable quantity of moisture; then that moisture or water is expanded by the operation of freezing, and heaves up the whole of the road. A subsequent thaw allows it to subside, but the connection between its parts being disturbed and broken, and the materials loosened, the first heavy weight that passes over them will go quite through, if only of moderate depth; or cut them into ruts when the depth is great. The substratum too is reduced to a semi-fluid state, and by the pressure of the hard materials and heavy weights, it is forced to the surface as the only means of escaping. If it is attempted to scrape this dirt away directly afterwards, much of the stone or gravel will unavoidably be mixed with it, and also removed. Whilst it remains, the road is scarcely better to travel over than a ploughed field ; and when removed, a hole is left on the surface." Extract from the sixth Report.
« In order to ascertain the most effectual mode of rendering the driving-way hard
half in length, was originally made by a private company, at a great expense, owing to the nature
and smooth, I caused an experiment to be made along a quarter of a mile, at the northern extremity of this road (the Highgate Archway Road), by constructing the roadway with a bottoming of Parker's cement and gravel, and with a coat of Hartshill stone laid upon it; and to ascertain what would be the comparative effect of using the same stone on the old surface of the road, I had a large quantity of it laid on between the arch and the Holloway road. The result is, that between the months of October and March last, full four inches of the stone on the old road, between the arch and the Holloway road, was worn away, where eight inches had been laid on, while not one inch was worn down where it was laid on the cement bottoming. This result corresponds with other trials where bottoming has been made with rough stone pavement.
“ The different parts of the Holyhead road which have been newly made with a strong bottoming of stone pavement, place beyond all question the advantage of this mode of construction; the strength and hardness of the surface admit of carriages being drawn over it with the least possible distress to horses. The surface materials, by being on a dry bed, and not mixed with the sub-soil, become perfectly fastened together in a solid mass, and receive no other injury by carriages passing over them than the mere perpendicular pressure of the wheels; whereas, when the materials lie on earth, the earth that necessarily mixes with them is affected by wet and frost, the mass is always more or less loose, and the passing of carriages produces motion among all the pieces of stone ; which, causing their rubbing together, wears them on all sides, and hence the more rapid decay of them when thus laid on earth, than when laid on a bottoming of rough stone pavement. As the materials wear out less rapidly on such a road, the expense of keeping it in repair is
of the sub-soil, which consisted of sand, clay, and gravel. A tunnel was in the first instance attempted to be driven through the hill, which, after having been executed for a considerable length, fell in ; the brickwork not being sufficiently strong to withstand the pressure of the clay and sand acting against it. After the failure of the tunnel that scheme was abandoned, and open cutting was resorted to.
The road-way was formed by laying on the natural soil a very large quantity of gravel and sand as a foundation, and this was covered, to a considerable depth, with broken flints and larger gravel. The carriage-way, however, notwithstanding this quantity of materials, was so heavy, loose, and difficult to draw over, that many carriages and waggons continued to go over the old steep road, and the company in consequence received little or no return for the capital they had expended in the work. This induced them to try every expedient they could devise, to improve the condition of the road, but without to take up all the road materials, and cover the subsoil with pieces of waste tin, over which gravel, flints, and broken stones were placed. All this, however, was of little or no use: the road continued imperfect, and even dangerous for fast coaches; the consequence was, that the Parliamentary Commissioners received complaints and petitions from coach-masters, and other persons who had occasion' to work horses over this road, praying that they would cause an examination into the state of the road, and have the defects remedied.
One of the schemes resorted to was,
proportionally reduced. The expense of scraping and removing the drift is not only diminished, but with Hartshill stone, Guernsey granite, or other stone equally hard, is nearly altogether avoided.”
In consequence of these petitions, a Select Committee of the House of Commons, in the year 1817, examined several witnesses upon the state of the road, and, amongst others, a director of the Company, Mr. Hoggart, who stated, that the annual expense of keeping the road in repair was 4201.
Notwithstanding the investigation which then took place, the road, as may be seen from Mr. Telford's Annual Reports to the Parliamentary Commissioners, still continued in a very bad and imperfect condition.
In 1829, the Parliamentary Commissioners made an arrangement with the Highgate Archway Company, for taking the road under their management, and for borrowing from the Trea
sury a sum of money to put it into complete repair. In order to accomplish this, several experiments were tried by draining the surface and subsoil, and by laying on a thick coating of broken granite ; but from the wet and elastic nature of the subsoil, the hardest stones were rapidly worn away by the wheels of carriages, but much more by the friction of the stones themselves against each other; for, in a very short time, they were found to become as round and as smooth as gravel pebbles, even at the bottom of the whole mass of road materials; it was therefore evident, that to form a perfect road, which might be kept in repair at a moderate expense, it was necessary to establish a dry and solid foundation for the surface broken stones ; but as no stones could be obtained for making a foundation of pavement but at a very great expense, a composition of Roman cement and gravel was suggested by Mr. M`Neill, and this, on trial, was found to answer effectually. The manner of laying down this cemented mass, and constructing the road, is fully detailed in the following evidence, given by Mr. M`Neill before a Select Committee of the House of Commons, in May, 1830: –
“ Are you the resident engineer under Mr. Telford, on the road from London to Shrewsbury ? Yes.