Twelve-Inch Main Lowered While Under Full Pressure
An interesting account of the lowering of a 12-inch water main while under full service pressure is contained in the annual report of the water commissioners of Middletown, Conn. In all 1,500 feet of the big pipe were moved to conform to a new street grade. The methods employed are best described in the following excerpts from the report:
A profile of the pipe line was obtained by digging test holes over the water main at stations of the survey made for the improvement of the street and running levels. The profile of the water main thus obtained was very irregular and far from being parallel with the grade of the street. At many points it was indicated that it would be necessary to lower the main a maximum of 2 ft. in order to bring it with its gates and services below frost line, and that the total length to be lowered would be about 1,500 ft. All of the services in the street which had not been renewed in recent years were renewed with leadlined pipe and lowered. After this was completed a trench was dug along the 12-in. water main down to the proposed new pipe grade at each joint and wood blocking placed under each joint. The earth was then excavated between joints to pipe grade. The first section to be lowered was 700 ft. long. The water main and a hydrant were lowered for means of jack screws placed in pits under the spigot end of each joint with wood blockings. The lowering of the main in this section was successfully accomplished with the water mains under pressure and without cutting the water main or hydrant branch. The joints were of the usual bell and spigot type with 3-in. sockets calked with oakum and lead. This pipe was originally laid in 1896 and the exterior of it was as good as new; in face some of the paint markings upon the pipe were as bright as the day it was placed on the pipe. During the process of lowering this pipe no trouble was experienced with leaks. It was apparent that the method of using jack screws and blocking and the necessary jack screw pits could be improved upon in the next section of 800 ft. Therefore chain hoists with 6×6 timbers laid across the trench as supports were used in lowering this section in which were two intersecting street mains and one fire hydrant. This method was a saving over the jack screw method, in excavation, cost and time of lowering, as it was much more rapid and it was useful also in assuring the safety of operation. The greatest number of hoists that were used simultaneously was four. This method proved to be very successful from every point of view, and no trouble from leaks was experienced in this section. It was not necessary to disconnect or cut the main and hydrant branches and street branches to be lowered, and the mains were kept under full service pressure. It was necessary to disconnect the house services for only short periods. All of the gate valves in this section were carefully inspected and spindles repacked and all pipe joints were recaulked.