India and Indian Engineering. / Three lectures delivered at the Royal Engineer Institute, Chatham, in July 1872

by J. G. Medley

India abounds in rivers, streams, and watercourses of various kinds, and therefore the subject of [Bridges] is a very important one to the engineer; but before describing any of the permanent structures that have been built, it may be useful to say a word as to the temporary expedients employed on lines of road, when money is not forthcoming for the more expensive forms of construction. The first of these is a sort of Irishman’s bridge—it is no bridge at all; you go through the water instead of over it, by means of Paved Causeways, which are often employed on watercourses which contain no water for the greater part of the year, and are only flooded occasionally. The banks are cut down to a gentle slope on each side, and a pavement or solid flooring of masonry or concrete is built to afford a firm roadway for vehicles. If the water is too deep or the stream too strong, the traveller must wait till the flood goes down. You will find a good account of such a pavement across the River Soane in No. 2 of the ‘Professional Papers.’ It is a mile long by 12 feet wide, and answers its purpose very well.

On many of the great lines of road, Boat-Bridges are in use during the low-water season, which are taken up and replaced by ferry boats during the rains. The boats used are the ordinary native boats, with a platform laid on balks and saddles; but they are often troublesome when the river is falling, owing to the necessity of removing some of the boats before they are left high and dry. Cylindrical Pontoons are preferable in this respect, and are often used. There is a pontoon bridge over the Jumna at Agra, and a very fine one at Cawnpore, over the Ganges. You will find descriptions of these in the ‘Professional Papers.’

On the Hill roads, temporary bridges are very common. Some are very simple, consisting of a single suspended cable, on which is a sort of travelling cradle in which the passenger sits, and is hauled across by tackle from the shore end. Others consist of a rope for the feet and two others for the hands, the three being kept apart by triangular sticks, and if you are of an acrobatic turn of mind, they are convenient enough. More ambitious specimens have a suspended platform of bamboo 3 feet wide; and a neat Wire rope bridge of 200 feet span was built over the Jumna two years ago by some young officers who went out, with the help of the native sappers.

You will find another peculiar kind described in the ‘Treatise,’ and in No. 166 of the 4 ‘Professional Papers,’ put up by Major Lang, R.E., on the Hindustan and Thibet road. These are Sanghoos, consisting of beams weighted with stones, and gradually projecting one over the other until they meet in the centre. A Rope Suspension bridge worth study, over the Chenab, is described in No. 202 of the ‘Professional Papers.’ I would also draw your attention to the account of the Iron Suspension bridge over the Beosi at Saugur, described in No. 30 of the ‘Papers,’ erected forty years ago by an infantry officer with the unskilled labour of the district, and using materials procured on the spot. It is a good specimen of the way in which an officer is often called upon in India to exercise his mother-wit, and dispense with the ordinary means and appliances.

Of more permanent bridges, Timber structures are not much used in the plains, because wood is generally very expensive, and the extreme heat and damp loosen the joints and threaten decay to the timbers. You will, however, find several described in the books so often referred to, notably one over the Barra river, near Peshawur, by Lieutenant (now Major) Browne, R.E., one of my assistants at Roorkee lately.

Masonry Bridges of brick and stone are common enough, and you may often have to construct them. You will find several described in the ‘Papers,’ and the descriptions of the Morhur and Markunda bridges are especially good and suggestive. The piers and abutments of such bridges are generally founded on well-cylinders in the way I have already described, the number varying from three to ten according to the weight and size. In the bridges on the Lahore and Delhi Railway, great economy of construction was attempted by making each pier of one single well-cylinder, 12½ feet diameter inside, supporting a pair of lattice girders carrying a single line of rails. Now, as these were sunk from 40 to 50 feet below the bed, and had an additional height of some 20 feet to the girder above, the stability of such a long slender column was somewhat doubtful; and when the river scoured out its sandy bed down to the clay stratum in which the cylinder rested, the force of the stream, acting with such a leverage, threw over several of the piers;—at least, in this way I interpret the failures that occurred in these bridges last year. Had each pier been composed of two cylinders (one for each pair of girders and line of rails), with the two braced diagonally together, they would probably have stood.

I have not spoken of the calculations necessary for the Discharge of these rivers, and the Waterway of these bridges, because it is too long a subject to be treated of in a lecture. I will only say here that in no one single point is the Indian engineer so liable to make mistakes; there is nothing that requires so much study, and failures on account of insufficient waterway are of every-day occurrence in that country. And even when your bridge is built, and you have good reason for believing the waterway to be ample, so treacherous are these streams, that their course may change in a single night, and your abutments may be taken in reverse. In the bridge over the Sutlej, thirty-eight spans of 110 feet each were provided for the stream, and yet, when I saw it, not a drop of water was going under the bridge; the stream had shifted while the bridge was being built. Twenty other spans have since been added, the embankments have been made very massive and defended by spurs and groins at a great expense against the action of the river; yet there is no certainty that the river may not attack the embankment at some other point in the breadth of its valley (which is 5 miles across), and force its way through, leaving the bridge high and dry. By the last mail I see that one of the piers has failed, and all traffic is stopped.

Of Iron Girder Bridges there have been many fine specimens erected since the railways have been begun. Except a few small ones which have been constructed at Roorkee, they have all been made up in England, sent out in pieces, and erected on the spot. I especially commend to your notice the paper on the Tonse Bridge, in the ‘Professional Papers,’ as giving an excellent idea of the difficulties of this kind of work.