CHAPTER XIII LARGE MAINS Examples of long pipes and aqueducts Conspicuous examples of American cities which have gone far afield for water are Los Angeles, which brought in a new supply from 235 miles away; San Francisco, 154 miles; New York, 120 miles; Tulsa, Oklahoma, 60 miles; Pheonix, Arizona, 32 miles; Butte, Montana, 27 miles; Denver, 25 miles; and Norfolk, and Portsmouth, Virginia, about 20 miles each. In Canada the city of Winnipeg brought in a new supply a total distance of 98 miles, while Victoria went 38 miles for its water. In Australia the Coolgardie pipe line is 351 miles in length, while the Apulian Aqueduct now being constructed to supply 266 communities in Southern Italy will have 152 miles of main trunk conduit and 841 miles of main and subsidiary branches leading therefrom. The near future will doubtless see a very large amount of capital invested in supply mains, so that the economic design of these mains is a live and important problem. Aqueducts The largest of these supply mains, commonly known as aqueducts, are generally, except at valley crossings, constructed of masonry built in trench or on enbankment or are masonry lined tunnels. They are generally placed at the computed level of the hydraulic gradient so as not to flow under pressure. Inverted syphons At crossings of valleys, inverted siphons, often called just siphons, are required, flowing under pressure. Some recent large siphons have been tunnels, called pressure tunnels, excavated in rock beneath the valleys. Where pipes are used for siphons they are essentially like other supply mains which form the subject of this chapter. Types of pipe available As a result of developments in modern manufacturing the engineer charged with the design of a supply main has at the outset four principal materials to choose from; viz., cast iron, steel, reinforced concrete, and wood. In the case of each material, there are two or more types of pipe available. In cast iron there are bell and spigot pipe, made in accordance with the standard specifications of the American Water Works Association; or, what is known as the "high tensile strength" bell and spigot cast iron pipe. For submarine work many types of cast iron ball and socket jointed pipe are available and these are sometimes used also under railroad tracks to reduce leakage. It is also possible to secure cast iron pipe with a mortar lining. In steel pipe the principal types are riveted, spiral, lock-bar and hammer-weld pipe, with various types of joints. Mortar lining has sometimes been used for steel pipes of the larger sizes. In reinforced concrete, there are available pipe cast in place and several types of precast concrete pipe, with joints at intervals of from 3 to 12 feet. The field of wood stave pipe offers the machine banded and continuous stave types. The staves themselves might be redwood, fir or pine. Period of use The use of cast iron pipe dates back over two hundred years; of steel pipe approximately forty-five years; of reinforced concrete pipe, about thirty-five years; of wood stave pipe, about forty or fifty years. Pipes of wrought iron plate were in use before steel pipe. Sheet iron pipe lined and covered with cement mortar has seen upwards of fifty years of use. Physical properties of various types of pipe Carrying capacity Cast iron pipe, lock bar and hammer-weld steel pipe, reinforced concrete and mortar-lined steel and cast iron pipe, and wood stave pipe all have smooth interior surfaces and comparatively high coefficients of discharge when new. For equal sizes it is doubtful if there are any strictly comparable gaugings which will prove con |