Foundations or No Foundations ?
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By Col. R. E. B. Crompton, C.B., M.Inst.C.E., Chairman C.M.U.A.
Those who followed the proceedings of the recent Road Congress at Paris wili most probably have noticed that the Continental engineers spent much of the time in discussing questions which have long since ceased to interest our English engineers, one of them being as to the .advisability of putting concrete foundations under the sett paving of the roadways in cities, Most English engineers are under the impression that this question was settled years ago, and that such foundations are always necessary. This, however, does not appear to be the case in France, or on the Continent, a large proportion of the sett paving met with in provincial towns there being simply laid in sand. At this admittedlyimportant International Congress, our Continental friends seemed to incline to the English practice, and a resolution was passed that in most cases such concrete foundation was desirable.
11though the English engineers did not benefit from this and other discussions of the same class which took place in Paris, the English-speaking engineers, i.e., those from the United Kingdom and America, did benefit greatly from the interchange of views on similar matters. One curious fact made itself fully evident, and that was that, although most of us have believed that a not inconsiderable proportion of our main Macadamised roads were constructed with a foundation of hand packed large stones, on which the ordinary coating of road metal was laid, rolled and consolidated, this method cannot be properly called a " Macadamised " road. A road with such a hand-packed foundation, and with consolidated broken-stone metalling above it, ought properly to be called a " Telford " road, whereas the Macadamised road is one which is constructed on the levelled formation surface with broken stone throughout, although in some cases this broken stone may be graded. It was easy to learn from the conversation of the English and Scotch engineers that a far larger proportion of the roads of England than anyone has any idea of are constructed purely as " Macadamised " roads, i.e., that no hand-packed foundation is used, and that this method of construction. applies to great lengths of our best roads, so that it by no means follows that this last method is inferior to that of Telford.
After all, the most important matter for the successful maintenance of a road appears to lie in the fact that the water should not be allowed to find its way under the surface of the road, either by direct percolation from above or by the side infiltration of any land water. The latter contingency can be, and is generally, provided against by suitable side drains, but percolation through the surface can now, only, for the first time, be provided against by making the metalling waterproof. The interesting question which now presents itself is what will be the ultimate effect of waterproofing a well-made Macadamised road. Many road engineers consider that a waterproof and well-consolidated road, made of good road metal, the intersticial spaces of which are filled with waterproof bituminous or tar material, can resist fast traffic, even if the thickness is cut down to a point far below that hitherto considered necessary for a first-class road of ordinary Macadam, where downward percolation must always take place. If this opinion is warranted by further
experience in road construction, it will have a most important bearing on the cost of new roads required to develop new countries, the chief cost of such roads being the carriage on suitable road material, which is often so great as to be almost prohibitive of extensive road making, but if— as appears quite probable—we find that one ton of road metal, waterproofed, can do the work of two tons of the same material left in its porous water-bound condition, an enormous impetus will be given to roadmaking in many districts in America, Australia, Argentine and other countries. This is one reason why all of us who are interested in commercial motors and their future development ought to take the keenest interest in the new developments of road-making. During the forthcoming winter, we shall watch how far the waterproof roads already laid stand the winter. There are now in existence lengths of waterproof roads of all classes. These may be graded from the best and consequently most expensive roads, which are made up with waterproof material front the bottom of the metalling right up to the sur face, and which in the future may cost from is. 6d. to 35. a superficial yard for this surfacing, down to the least costly, amongst which we may class the recent work that has been carried out on the Wandsworth roads and on the Hertfordshire roads, near St. Albans, Hatfield, and elsewhere, in which a road, immediately after being resurfaced with the hest road materials free from dirt or water-binding, has been sprayed under pressure with suitable tar. In this simple but cheap way, surprising results have been obtained. The tar has penetrated to nearly an inch from the surface, although the quantity used has been very small, and front this cause these roads have never been slippery, and the tarring has been carried out successfully
and without diminishing the tractive power of horses or of cars on gradients up to i in 21). The forthcoming winter will enable us to see whether this very small quantity of tar, only penetrating to an inch from the surface, will be sufficient to hold that surface together then, and, of course, if the winter is a severe one, and if we have long frosts and coatings of snow remaining on the roads for a considerable time, we may well expect to find that under such difficult circumstances this convenient and cheap method of waterproofing may be found short of perfection. At the same time, even if this is found to be the case, we ought not to he discouraged, as the cost of such treatment is so low that, even if it only prevented the road from breaking up and producing quantities of dust in summer, the treatment, which rarely costs more than -e:40 a mile for a road seven yards in width, would still be advantageous to the road user. It follows, therefore, that the problems our road people have to examine during the forthcoming winter will be to see which of these two classes of road is on the whole best for the road makers and for the road users, efficiency in both cases being governed by financial considerations_ A waterproofed road may prove to be strong enough, with reasonable penetration, consolidation, and depth of metalling, to carry heavy traffic without that fatal opening and loosening of the surface, and thereby to demonstrate that costly foundations are not the only solution.