« السابقةمتابعة »
work as efficiently as an experienced well-sinker. On the application of the Jham (vide supra) the top of the cylinder is loaded with logs of wood and heavy articles that may be at hand; a fork-like prop with a pulley is fixed in the ground, so that the rope which runs over the latter, and to which the Jham is fixed, should run centrically over the well; the Chah-kun then descends with the Jham, and with his hands and feet (for the natives use both with equal facility,) forces the instrument into the soil until it gets properly loaded, when it is drawn up, the contents removed, and the same operation is continued until the work is completed. After the soil has been removed beyond five or six feet below the surface of the water, the Chah-kun's duty is constant diving.* I have known them to remain half a minute and nearly a minute under water without any respiration. Each man is relieved at the end of the hour, and in hot weather the cold that they suffer in their escape from the well is severe to a degree; large fires are kept burning for them to recover themselves at, and a liberality on this point is one of the chief agreements between the well-sinker and his employer. In the cold season the annoyance from change of temperature is infinitely less, and the people themselves have often assured me that they could in this weather do twice the quantity of work, and with one-half of the labour to themselves, that they could do when the weather is hot, and when the evaporation was so rapid.
In describing the process required for the sinking of one well for common village purposes, we have only now to shew how the application of a number of these wells in conjunction can be turned to account for the purposes of securing a good foundation; for this purpose I shall give plans and sections of some of the works on the Doab Canal, explaining the method adopted in these works, and also shew how, under different circumstances, the same plan of foundation has been used with equal effect.
The course of operations depends on whether the wells used in foundation are placed close together, or at a distance. For piers of bridges with extensive waterway and heavy superstructure the former is usually adopted; in other cases, the wells are placed four feet apart, and connected together by masonry arches, upon which the wall, pier, or building is constructed.
In Canal works, however, it is often an object to obtain a running line of wall for foundation unbroken by divisions or points of separation, through which the substrata, when consisting of a loose sandy soil,
* In very deep wells, where the neemchuck exceeds twenty-five feet from the water's surface, the Jham is worked by long poles fixed to the handle, and the work is most tedious.
might escape, especially where there is a head water with springs opposed to it. In locks or descents, for instance, constructed in sand, where the subsoil in addition to its own natural spring water has that of the Canal to act upon the flooring of the lower chambers, there is a considerable tendency to the removal of the sand under these lower floorings, which seriously affects the stability of a work, and is only to be provided against by enclosing all the subsoil in continuous lines of foundation. I shall hereafter describe a remedy invented by Col. John Colvin, C. B. of the Engineers, formerly Superintendent of the Delhi, and Superintendent General of, Canals; but in the meantime it is evident that where wells or cylinders are used, the continuity of a wall is imperfect under any circumstances; for place them as close together as possible, there is still a separation-the curtain so much desired is wanting. The methods adopted by me in the two cases, first, where wells are sunk close together, or leaving a space of six or eight inches, which is the least that can be safely given, and, secondly, when at a greater distance apart, are these-piles, and as the English engineers now term it, concrete (an article which, I may observe in passing, has been in use in Hindoostan from time immemorial); the former in the works on the Doab Canal varying from sixteen to five and a half feet in length, and the latter laid in as deeply as possible between the piles, and allowed to stand for some days to settle and indurate. The piles are made of young Saul trees (Shorea robusta) cut in the forests in the northern slope of the Sewalik hills, in the Deyra Dhoon; or when only five and a half feet long, of the species of rafter called by the natives Kurri, the smaller sort averaging from ten to twelve feet long and three and a half inches square, sawed out of Saul timber in the forest, and imported in immense abundance into the plains swung on the back of bullocks by the Brinjarris, or class of people who lead a roving life, employing their cattle in this species of work. The concrete consists of kunker, an alluvial lime rock peculiar to India-of stone boulders from the river broken into fragments-the gutta or refuse of lime kilns, mixed with a proportion of cement, consisting of two or three parts of soorkhee, or pounded brick, and one part of the best stone lime thrown in and well mixed together with a pole, sharp at one end and blunt at the other; the former to stir up the mixture for a certain time, and the latter to ram it down until it is properly placed in position.
The figures in plates 1 and 2 represent these methods in detail, with the neemchuck and tools used by the well-sinkers; and in plate 4, which is a plan and section of falls and locks as constructed on the Doab Canal, the application of both will be easily recognized.
The depth to which a cylinder of six feet in the diameter can be sunk during the day by one party of well-sinkers through a sandy stratum as far as ten feet, varies from two and a half feet to four inches. It is desirable when the well has to be sunk to this depth only, to expedite the depression of the three or four last feet as much as possible, so as to get the cylinder to its full depth, without leaving it during the night, and allowing the loose soil to settle round it, and give it a firm embrace. It is very difficult at times to free the sides of the cylinder from the hold which the sand has in this case upon them, but even with a very heavy weight applied to the top half a day may be expended in this way, without getting the well to move at all-a remark equally applicable in pile-driving through sand, where the advantages of driving the last pile that is driven during the day to its full depth, is well known. I have seen a pile, length twenty feet and diameter eight inches, which has been driven ten feet on the previous evening, resist on the next morning the weight of the pile engine for forty successive strokes-the weight of 250 lbs. falling through a space of ten feet, the head of the pile becoming perfectly shattered and useless. The following table will give an approximation to the expense of sinking cylinders of the above mentioned diameter to a depth of ten feet, and although the difficulties attending the operations from which this table was formed were greater than would be generally experienced, a very tolerable idea of the expense of well-sinking will be exhibited.
Soil, sandy, mixed with clay, but free from stones or kunkur; full of springs, with the canal head water ten feet above the point at which the cylinder commenced sinking; outer diameter of well six feet, and in some instances eight feet, and inner diameter four and six feet respectively; machinery employed night and day in keeping the water down to the level on which the wells were built; windlass used with the Jham; period of operation between January and May.
Or average per running foot Rs. 2:0:4
The cost of building a cylinder of the above diameter, viz. 6 feet and 10 feet high, may be thus
giving the average cost of well-sinking, using a cylinder of six feet in diameter and carried to a depth of ten feet at Rs. 4: 13:2 per running foot. In the above table, however, as I before remarked, the items are dependent on difficulties which in well-sinking from a plain surface-from the level of a garden for instance-would not be met with. In wells situated in this way, and of similar dimensions in every respect to those upon which our data are formed, the expense varies at from three rupees six annas to four rupees per running foot, the difference depending on the cost of labourers-the price of materials remaining constant. The masonry of well-building I have generally found to vary from eighteen to twenty rupees per 100 cubic feet.
In wells of from sixteen to twenty feet depth the expense per running foot has been found to vary from Rs. 7-8 to Rs. 8-8, using the cylinder above noted; to a greater depth, however, they require to be of larger dimensions; but it would be interesting to discover the progressive advance in expense on each ten feet of well-sinking; it would possibly advance in a series with a common multiplier of two, leading to the following table as an approximation-the upper line representing depths of cylinder in feet up to fifty, the second the cost per running foot, and the lower the actual cost of well at each depth as noted in the upper line.
4 Rs. 40 Rs.
8 Rs. 160 Rs.
30 ft. 16 Rs. 480 Rs.
The two first columns are formed on my own practical observation, and the third is from the cost of village wells, extracted from the statistical notes of the Revenue Surveyors in the upper portion of the Doab, plus the expense of undersinking the first sixteen or twenty feet, which in village wells is generally built up. Whether the progression which holds in these may be extended further, as I have proposed in the fourth and fifth columns, may be easily shewn by reference to the Engineer officers who built the bridges on the East Kallee Nuddee, and Hindun rivers; (to Captain Debude, and Lieutenant Alcock,
* The M.S. is blank in these spaces.-EDs.
these notes are especially addressed); the piers of the Hindun bridge resting on wells up to the limit of the table above proposed.
It must be recollected that the cylinders are supposed to be undersunk from the commencement through a sandy soil, and with spring water at the surface-as must usually occur in foundations where the The cost of application of them for that purpose would be necessary. village wells, which although thirty or forty feet deep are only undersunk on reaching the springs, is proportionably less.
With reference to the value of obtaining a connected curtain, or line of running wall in foundation, where the interference of spring water renders undersinking necessary, Colonel Colvin, C. B. of the Bengal Engineers, proposed a plan of sinking square masses or parallelopipedons of masonry, piercing these masses by wells, as represented in Fig. 1. Pl. 3. The plan succeeded in every respect. In those of from ten to fifteen feet long and four feet wide, undersinking to a depth of ten feet in sand mixed with small shingle was carried into execution with perfect success in the foundations of the dam over the Somhe river. Water was, at the point where the dam had to be constructed, immediately on the surface; the object of the dam was to retain the supply of and water to a considerable height to throw it into the Delhi Canal, maintain a supply during the dry months. Circular wells were objectionable for the reasons which I have before explained, and it was a desideratum to get such a foundation, that the head pressure of water should affect the leakage under the dam as little as possible. Fig. 1. Pl. 3. will explain the method adopted, the spaces between the boxes on the first row being covered by those in the second line.
The method put into practice in sinking these masses is similar to that in cylinders, but greater care is required in regulating the operation of the well-sinkers, so that the mass may be lowered equally. The curb, or neemchuk, is a platform of wood equal in size to the base of the masonry, with round or oval holes cut for the wells, as shewn in Fig. 1. Pl. 3. I have used these masses in lengths of twenty-one, feet, by four feet wide, to a depth of ten feet, with perfect success, giving three wells in each. I should however limit the dimensions to fifteen feet by four feet, with two wells elliptical, five feet by two and a half each, which with proper care will be sunk to a depth of ten feet through sand without any difficulty. There appears no reason why a whole foundation of a work within certain limits might not be sunk in this way. It is often a difficult matter to obtain foundation for a bridge with an arch of twenty feet span where the soil is sand although the drainage is not liable to freshes or any violence of current. A bridge of this sort, with a roadway of fifteen feet, would