each wall to provide a bond between old and new work. Great pains should be taken, before placing new concrete in contact with an old surface, to remove from the latter all dust, loose stone, laitance, or scale, wet it thoroughly, and wash or thinly plaster it with cement grout first before placing the new con crete. Foundations. Piles are ordinarily used for sewer foundations in soft soil. They usually support a timber platform, but in FIG. 62.-FIFTY-TWO-INCH CONCRETE SEWER. some instances concrete is placed directly upon and around their heads. For driving them, the ordinary pile-drivers are used, or they are sunk by the water-jet. If they are to support platform timbers they must be driven carefully to line and sawed off accurately to grade. It will sometimes be advisable to drive the piles before the excavation has proceeded very far, using piles considerably longer than actually required, as the jarring of the banks of the trench may thus be avoided, as well as the inconvenience of moving the driver through or over a trench full of braces. The objection to this plan, aside from the cost of the additional length of the piles, is that they interfere with the excavation. If a platform is used without piles, sills should be placed under the planking, although in the case of small sewers these may consist of 2-inch plank only. Such platforms may serve to distribute the load and prevent local settlement and motion of the soil during construction, while the loading due to the sewer is non-uniform and continually changing, even though they are of little service in furnishing support to the completed structure. Manholes and Flush-tanks. When laying a pipe sewer, the manholes are not usually constructed until the sewer has been completed beyond them, pipes being omitted from the line where . the manhole comes, including the length of pipe that enters and the one that leaves the manhole, these last being laid when the manhole is built. Manhole bottoms are most conveniently made of concrete. If the soil be soft or wet, it is well to place a plank platform under the concrete. If the soil is not such as to assure the support of the manhole walls without any settlement, special precautions against settlement should be taken, as by using piles, providing a wide footing for the walls, or building steel beams into the bottom that extend across the manhole and under and possibly beyond the walls. The channel through a pipe-sewer manhole is sometimes built of brick, but a split pipe is better. If brick be used, the inside of the channel should be plastered with a coat of neat Portland cement. (If any branch channel in a manhole is not to be used at once, it should be closed temporarily to prevent deposits forming in it.) The bench may be built up of brick plastered on top with cement, or of concrete. The author prefers to make the whole manhole bottom of concrete, a wooden or sheet-metal core being slipped into the opposite pipes and spanning the manhole to give the shape to the channel; or the splitpipe invert being put into exact position and held there by braces until the concrete sets under and around it. In leaving the manhole opening in a brick sewer, the end brick in every alternate course of the outside ring may be laid radially, thus presenting toothing protruding at right angles to the sewer barrel. In this, steps with horizontal treads can be built of brick trimmed to the necessary shape, from which the manhole can be carried up without danger of its sliding off the sewer. The brick in a manhole may be laid as all headers, all stretchers, all on end with their edges exposed or a combination of these. Bats may be used in large or small proportion, or not at all. A strong manhole can be built by using three courses of stretchers to one of headers, all whole brick, until a diameter of about 3 feet is reached, and from there to the top using three courses of square bats to one of headers. The outside of the manhole should be plastered as the wall is built, since it may be impossible to reach it afterward. The head should be set and the opening back-filled as soon as the brick-work is completed. Flush-tanks are built in a manner similar to the above. These, except at the very top, and catch-basins and inlets, are usually larger in diameter than manholes, and are built throughout of whole brick. Extra care should be taken to have all joints filled with cement and tight, and the work well bonded. After the cement in flush-tanks and catch-basins has fully set, they should be given on the inside two or three washes of neat-cement grout, laid on with a whitewash or similar brush, care being taken to cover the entire surface with each coat, which should be allowed to dry before the next is applied. This will seldom fail to give a tight wall. Concrete would seem to be especially adapted to flush-tanks, as it can be made watertight more readily than can brick. The concrete should be made of a rich mixture, with an aggregate especially porportioned for securing imperviousness. Gravel will generally give more impervious concrete than stone. It should be mixed just wet enough to flow into place in the form when joggled with a shovel. No water should be turned into the trench for flushing or other purposes before the cement in these appurtenances, as well as in the sewer, has set. CHAPTER XIII MAINTENANCE ART. 57. NECESSITY FOR MAINTENANCE It is the too general rule that when a city has constructed a system of sewers it considers its duty done, and permits any kind of connection to be made with them, by anybody and in any way, and takes no more thought of its sewers until compelled to do so by some obnoxious conditions therein. This is all totally wrong, and even criminal. While it is not probable that any well-designed and constructed sewerage system will ever become worse than no system at all, it will not work at its best efficiency and free from objectionable conditions if unattended to, any more than would any mechanism. Moreover, a considerable expense has been incurred to provide sanitary sewerage for the citizens, but if careless or penurious landlords or plumbers or ignorant householders are permitted to construct between the sewer and the house, or in the latter, cheap and unsanitary house-connections and plumbing fixtures, the health of the citizens is endangered and complete return for the outlay for sewers is not received. No dread of paternalism should interfere with the proper performance by the city of its manifest duty to require that all sanitary" piping and fixtures throughout the city are sanitary, and the sewers should be in the charge of an experienced officer who is held responsible for their cleanliness and efficiency. The first necessity for this oversight will come with the connection of the dwellings to the sewers. ART. 59. MAKING HOUSE-CONNECTIONS No house-connections should be attached to a sewer except in the presence and under the direction of a city inspector and by a party who is under bond to follow the city's regulations for such work. No house should be allowed to connect with the sewer until its construction is entirely completed, including plastering and sanitary fixtures, owing to the danger that mortar and rubbish may otherwise be admitted to the sewer. No connection should be made with a sewer except at a branch provided for that purpose. If there should be no branch within a short distance, one may be inserted in a brick sewer by cutting through its wall and building a slant firmly in place or, in a pipe sewer, by removing a pipe and inserting a branch pipe in its place. If 3-foot lengths of pipe were laid in the sewer a few 3-foot lengths of branch pipes may be kept on hand for this purpose. (Branch pipes are generally used in 2-foot lengths.) To remove a pipe from a sewer it may be broken to pieces with a hammer, care being taken not to crack the adjacent pipe. Then, with a cold-chisel used with some care, the upper half of the bell facing this opening is broken away and likewise the upper half of the bell of the branch pipe to be inserted. This is then dropped into place with the branch on the wrong side and revolved, thus bringing to the top of the sewer that part of both pipes where the bell is wanting. The joint is then made, Portland cement being substituted for the missing portions of the bells. In breaking the cap or plug out of a sealed branch, care must be taken not to break any part of the pipe. If broken, the pipe should be replaced by a new one, as above. If the branch is cracked, it may be left in, but should be surrounded with rich cement concrete well compacted. It is absolutely not permissible to cut a hole into a pipe sewer and insert the house-connection therein, as it is almost impossible to obtain a junction that will not leak or to prevent the connection-pipe from protruding into the sewer. The house-connection should never be larger than the branch which it enters, but should preferably be smaller. A 4-inch pipe is large enough for any residence or small hotel or, in general, for 90 per cent of all the buildings in most cities. On a grade of 40 it can carry the simultaneous discharge of ten |