226

Repairing Old Roads.

Length of base, 20 feet; length of top, 14 feet; height, 3 feet cross section, width of base, 7 feet; width of top, 1 foot; height, 3 feet; sectional area, 12 square feet; contents, 204 cube feet. The diagrams in the margin will show this clearly, the following being the mode of calculation:

The same principles apply to stacks of any dimensions, but it will be found convenient to have a standard measurement and supply the contractor with a wooden gauge.

In repairing or remetalling old roads, the surface of the road is to be well picked up and levelled, so that the new and old metal may bind properly: no part of the old metal should be removed and used as binding for the new layers.

A well made jhama road, laid with good picked material, should last without repairs, subject to ordinary town traffic, for three seasons: this, however, depends on the quantity and class of traffic.

Stone roads, or what are often called Macadamised roads (after Macadam, one of the first constructors of modern roads with broken stone), are laid with indigenous stone or ship's ballast broken into irregular cubes so as to pass through a ring of two inches in diameter. In Calcutta and its neighbourhood the stone used is either brought from Oodooa nullah in the vicinity of Rajmahal, and excavated from the low spurs of the Rajmahal Hills, or is ballast from Bombay, Melbourne or

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Stone or Macadamised Roads.

227

Mauritius. Laterite is much used in Madras, but is too

soft to stand much traffic. stones are the best kind. upon a foundation of stone boulders, or, where they are not procurable, on a well-laid soling of sound hard bricks. A stone road made without soling, though it may be, to all appearance, a hard sound road, will never bear heavy traffic, the subsoil will yield more or less under the superincumbent weight, and in long continued wet weather, especially with the tremendous tropical downpour of these latitudes, the mud will work up to the surface and the road will speedily become impassable. I do not overlook the fact that Macadam maintained that no foundation of large stones or other material was necessary even in the softest soil, but recommended that the foundation be made of broken stone the same as the surface.

Granite, trap, and hard limeAll stone roads should be laid

Where a good foundation of boulders has been first laid, a six-inch layer of broken stone will form a good lasting road; but where bricks are used over a soft subsoil, at least eight to nine inches of metal will be necessary at first construction to ensure a good trafficable road. The amount of traction power required varies very considerably on roads of different construction, and is much less in proportion to the strength and hardness of the surface.

It has been proved by experiment that, "on a well made pavement, the power required to draw a wagon was 33 lbs. on a road made with six inches of stone of great hardness laid on a foundation of large stones, the power required was 46 lbs. on a road made with a thick coating of broken stone laid on earth, 65 lbs., and on a gravel road laid on earth, 147 lbs.”

Stone for road-making must be broken into sharp

228

Construction of Stone Roads.

angular forms. They then wedge together into a hard compact mass. According to Macadam no binding material should be used, but in this country the use of binding is universal, and care must be taken that the binding used is good dry brick and lime rubbish without any admixture of earth or clay, which would make the road muddy during rainy weather, or where streets are copiously watered. The transverse section of the road should be gently convex. As footpaths are seldom used in this country, pipe drainage is not required; but there must be provision for letting the surface water pass freely into the side drains, which should be of sufficient depth to drain not only the surface but the whole formation. It should always be borne in mind that the best stone,—that is to say, the hardest and toughest, though perhaps more costly at the outset, is the least so in the end. The best material for stone roads, as before noticed, is tough granite. Water is the worst enemy to good roads; it is therefore one of the first principles of road-construction that they should be kept dry; no water being allowed to lodge on the road surface.

A useful material for raising and metalling lanes and byroads, where there is little traffic, is often available in towns where any large manufactories, mills or foundries exist, in the slag, cinders, ashes, and scoriæ from the fur

naces.

In some parts of England, and on the Continent of Europe, as in Silesia, slag is largely used in road-making. It is not available, however, in sufficiently large quantities here to make it of value for that purpose, but occasionally sufficient quantities of it, mixed with ashes and cinders, are procurable in suburban districts, to form a dry

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Shade Trees Beneficial or Hurtful?

229

substantial surface to small lanes and footpaths. It merely requires to be laid on the road surface, levelled and rolled with a light roller. Where there is little or no wheel traffic, it will last with a little attention for a long time, and add greatly to the comfort of the residents at a very small cost.

During the hot weather the stone composing road surfaces is very apt to work loose: all loose stones should be gathered up and removed, as they are not only likely to throw horses down or lame them, but each stone, as a heavy wheel passes over it, acts as a pick to loosen others, the mischief thus repeats itself, and the road, if neglected, soon becomes almost impassable. Great economy will result from a regular attention to, and immediate repair of any small portion of road surface which has worn out.

There is some difference of opinion as to whether trees are beneficial or hurtful to road surfaces. Some authorities consider that where trees are planted close to and overhanging a road, the droppings from the leaves injure the surface, and their shade keeps it from drying properly.

Others consider that they do more good than harm, by protecting the surface from extreme heat. I think that if the undoubted comfort to the wayfarer be added to the probable benefit, the balance is in favor of planting trees, so as to give the greatest amount of shade with the minimum of obstruction to traffic. American engineers hold, that shade is objectionable on earth roads though admissible on stone roads, and their objections, so far as they go, have reference more to the exclusion of the sun from the road surfaces in winter, when the roads are dangerous and slippery from frost, than to any other question.

230

Faulty Construction of Embankments.

The metalled portion of a road should not be less than sixteen feet, to allow vehicles to pass each other with ease.

Although probably few Municipalities have to undertake extensive works of this class, it may happen that those situated near the sea-board, or contiguous to the large tidal rivers, may require protective works of the kind, and a few words on the subject of constructing, protecting, and maintaining embankments may therefore not be out of place.

Whilst engaged in the construction and maintenance of such works, and the reclamation of tidal lands at Port Canning and in the 24-Pergunnahs, Sunderbunds, I had exceptional opportunities of studying the system of embanking them in vogue and in detecting its faults and weaknesses, and an improved system was introduced by me in the works under my charge, with great advantage. The common faults were: the construction of embankments with insufficient slopes, especially on the river face; the digging of the earth required for the construction from irregular holes or pits (locally termed chokats) from both sides of the embankment indiscriminately; and the throwing up of long lengths of rough embankment without beating, ramming, and consolidating the material whilst moist and plastic. The evils resulting from these errors were: first, the erosion and instability of the embankment from insufficient slopes; secondly, the holes from whence the earth had been dug being below high water level, the earth was kept constantly moist and soft, mud crabs burrowed freely through the softened base of the embankment, there was continuous percolation backwards and forwards as the tides rose and fell, and the embankment being thus rendered unstable, settled, and cracked, leaked,