A Treatise On The Principles And Practice Of Dock Engineering

250 DOCK ENGINEERING. probable result. Under such circumstances a suspension of pumping operations becomes imperative. Occasionally, leaks have been found to develop in the floor or sills of a lock or entrance subsequent to the completion of the work. In such cases the locale of the leak has been bored through to the underlying stratum and stand pipes, fitted into the holes, have been filled with cement grout, from a considerable height, to be cut off later as already described. This operation is best carried out at a time when the pressure of water within and without the lock is the same. Provided the holes are suffi- ciently close together, the whole of the underside of the floor may be coated in this way with a thin watertight diaphragm. Fissures in rock can be treated by the same process, and it is a common method for grouting up the interior of a cast-iron roller path after it has been adjusted by wedges and holding-down bolts to its proper level on the gate platform. Another course of treatment for cracks and fissures is that called stock-ramming, and consists in inserting into the borehole pipe lumps of clay worked up with cement or hydraulic lime, sand mixed with iron filings and sal ammoniac (rust cement) or stiff concrete, the material being forced home by blows from a heavy ram worked by hand or steam-power. Open joints may be caulked by rolls of canvas, partially tilled with soft cement. Large fissures are sometimes cut out, so as to form a rectangular recess into which a block of masonry is fitted, wedged up, and grouted. Cracks will often occur near the centre of a lock floor, owing to the unequal distribution of pressure over the foundation area, arising from the greater weight of the side walls. These manifestations of weakness may be prevented by adopting a floor, the section of which constitutes an actual or virtual inverted arch. The problem of the proper distribution of pressure over a lock area is a very important one, particularly if the strata be irregular and water- bearing. A variety of methods have been exemplified in different localities. If the ground be of an uncertain or treacherous character, such as clay interspersed with pot holes of quicksands, it will be well to effect the uniform distribution of the superimposed weight by the interposition of timber planking laid horizontally and arranged so as to break joint. A loose sandy foundation may be somewhat consolidated by driving a series of short piles at close intervals. A row of external sheet piling should not be neglected. An ingenious method has been devised for transforming a sand or gravel foundation into one of concrete, by impregnating it with Portland cement under air pressure. The following details relate to the manner in which the operation was carried out at the Port of Vegesack, near Bremen, on the River Weser : —* A pipe or shaft, lj inches in diameter, pointed at its lower end and per- * Neukerch on “ Constructing Foundations by forcing Cement into Loose Sand and Gravel by Air,” Min. Proc. Am. Soc. C.P., vol. xxx., p. 284.