(a) Timbered Sections. Excavation in short tunnels made beneath existing structures and/or under existing pavements or sidewalks, for the installation of pipe or conduits, shall be of sufficient size, height and width to permit the installation of the pipe and/or conduits, to permit proper bracing of the tunnel section and to permit ample room for the prosecution of the work and safety of the workmen.
Timbers used for support of tunnels shall be of good quality, reasonably straight grained and free from knots or other defects. All timbers shall, when placed for the support of the roof and sides of the tunnel, be fitted and wedged into place.
Cap and leg type of timbering, with sets not necessarily abutting, or longitudinal timbering, supported by vertical ribs, can be used, if the ground conditions warrant. If, however, in the opinion of the Engineer, ground conditions do not warrant this type of timbering, then there shall be installed a complete box or cant-type timber set, including necessary spreaders, cleats, sills and braces, with adjacent sets abutting.
All timbering, once installed in short tunnels, shall remain in place.
Pipe installed within short tunnel sections shall be in accordance with the governing general specifications for the type and kind of pipe involved.
Bell holes for B & S Sewer or Water Pipe shall be provided within the tunnel, if the type of timbering used does not involve the use of sills. If sills or flooring are used as part of the tunnel timbering, then all bell and spigot pipe shall be laid through the tunnel on blocking, and the space between the bottom of the pipe and the floor of the tunnel shall be thoroughly filled with sand.
Backfilling of all short pipe and conduit tunnels shall be made with fine sand, thoroughly rammed or flushed into place.
If shown on the drawings or designated in the project specifications, backfill shall be one- three-five concrete, or of the mix as designated in the project specifications.
(b) Jacked Sections. Jacked-in pipe lines beneath existing structures, pavements and railroad tracks shall be in accordance with the specifications contained in this subsection.
The size of the pipe to be jacked shall be as shown on the drawings and/or as designated in the project specifications. No pipe smaller than thirty-six inches in diameter shall be jacked into place. Pipe material may be either corrugated iron pipe or reinforced concrete pipe, as designated in the project specifications.
Corrugated metal pipe shall be fabricated from corrugated galvanized sheets, number eight gauge U.S.S. with the base metal made by the open hearth process. Rivets shall be made of the same material as the base metal, thoroughly galvanized. The base metal sheets shall be galvanized on both sides by the hot dip process at the rate of not less than two ounces per square foot of metal or one ounce on each side.
The corrugated pipe shall be especially fabricated for a jacking installation, with sections fabricated for field riveting. The pipe shall be furnished in lengths to suit the contractor. However, the sections should be as long as is possible for the contractor to conveniently handle and install.
Reinforced concrete pipe shall be of the tongue and groove type, conforming to the Standard Specifications for Reinforced Concrete Sewer Pipe, A.S.T.M. Designation C75, unless otherwise shown on the drawings and/or designated in the project specifications.
Adjoining sections of corrugated iron pipe shall be field riveted. Joints in reinforced concrete pipe shall be made with cement mortar and jute from the inside. Pipe shall be jacked-up grade.
A suitable approach trench shall be opened, adjacent to the top of the slope of the embankment. The approach trench shall be long enough to accommodate the length of pipe units to be placed and wide enough to provide sufficient working room. Guide timbers or rails for keeping the pipe on line and grade shall be installed in the bottom of the trench and heavy timber backstop supports installed at the rear of the trench to take the thrust of the jacks.
A timber bearing or pushing frame shall be built and furnished to fit or match the end of the pipe to be jacked, so that the pressure of the jacks will be evenly distributed over the end of the pipe. Two hydraulic jacks of sufficient power shall be used to apply pushing or jacking pressure.
Excavation shall be carried on from inside the pipe, eight to twelve inches ahead of the lead pipe. Excavation at the top and sides shall be approximately one inch greater than the outside periphery of the pipe. Bottom excavation shall be accurately cut to line and grade.
Once jacking operations are started, the work shall be carried on in successive shifts until completed, this to guard against the freezing of the line due to settlement and compaction of surrounding soil.
If the jacked-in pipe is to be used as a liner for an additional pipe or conduit, such additional pipe or conduit shall be laid and backfilled through the jacked-in pipe, in the manner previously specified in subsection (a) hereof, except as follows: water pipe installed in jacked-in pipe beneath railroad tracks shall not be backfilled.
If shown on the drawings, manholes of a size to accommodate the outside diameter of the jacked-in pipe shall be constructed on the two ends of the section or, in lieu thereof, the ends shall be suitably bricked off.
(Ord. 352. Passed 10-22-62.)