A. Trenches shall be excavated to the necessary width and depth for proper installation of pipe and shall have vertical sides. Minimum widths of trenches shall provide at least 12-inch clearance between the sides of the trench and the outside face of the pipe. The depth of trench shall be 6 inches below the bottom of the pipe barrel.
B. If the existing soil below the bottom of the pipe barrel bedding depth is found to be unsuitable, the Water Department may order extra excavation below the bedding grade.
C. Whenever unstable soil that is incapable of properly supporting the pipe or structure is encountered below the bottom of a structure, as determined by the Water Department, such soil shall be removed to the full width of the trench and refilled with bank run gravel containing no stone over 4 inches in diameter, placed in 12 inch lifts and thoroughly compacted. Crushed rock or screened gravel may also be used to replace unstable soils. No excavation shall be made below the limits of the excavation called for on the plans or herein specified without prior approval by the Water Department.
D. Pipe and fittings shall be laid accurately to the lines and grades indicated on the drawings. The deflection of alignment at a joint shall not exceed the appropriate permissible deflection as specified in the following tabulation:
Pipe Deflection Allowances
Maximum permissible deflection for full-length pipe*
* Maximum permissible deflection for 18-foot length, maximum permissible deflections for other lengths shall be in proportion to their length as compared to 18-foot long pipe.
Size of pipe |
Push-on Joint |
Mechanical Joint |
4 inches |
10 inches |
16 inches |
6 inches |
10 inches |
14 inches |
8 inches |
10 inches |
10 inches |
10 inches |
10 inches |
10 inches |
12 inches |
10 inches |
10 inches |
16 inches |
7 inches |
8 inches |
NOTE: The above-tabulated allowances are more stringent than those allowed by pipe manufactures and are the values recommended by the AWWA.
E. At all times when pipe laying is not actually in progress, the opened ends of the pipe shall be closed by temporary watertight plugs or by other approved means. If water is in the trench when work is resumed, the plug shall not be removed until all danger of water entering the pipe has been eliminated.
F. Push-on joints shall be made up by first inserting the gasket into the groove of the bell, then apply a thin film of special non-toxic gasket lubricant over the inner surface of the gasket that will be in contact with the spigot end of the pipe. The chamfered end of the plain pipe shall be inserted into the gasket and then forced past it until it seats against the bottom of the socket.
G. With mechanical joints, surfaces against which the gasket will come in contact shall be thoroughly cleaned prior to assembly. Tightening of the bolts shall be done in a diametrical opposite pattern to ensure equal pressure has been applied to the fitting and mechanical joint.
H. Prior to installation of sleeve-type coupling the pipe ends shall be cleaned thoroughly for a distance of 8 inches. A follower and gasket in that order shall be slipped over each pipe to a distance of about 6 inches from the end, and the middle ring shall be placed on the already laid pipe end until it is properly centered over the joint. The other pipe end shall be inserted into the middle ring and brought to proper position in relation to the pipe already laid. The gaskets and followers shall then be pressed evenly and firmly into the middle ring flares. After the bolts have been inserted and all nuts have been made up finger tight, diametrically opposite nuts shall be progressively and uniformly tightened all around the joint.
I. If effective sealing of the joint is not attained, disassembly of the joint is required and thoroughly cleaned and reassembled. Bolts shall not be over stressed to tighten a leaky joint or fitting.
J. All valves, fittings and appurtenances shall be set and jointed as indicated on the drawings. Where indicated or necessary to prevent joints or sleeve couplings from pulling apart under pressure, suitable socket pipe clamps, tie rods, and bridles shall be provided. Bridles and tie rods shall be at least 3/4 inch in diameter except where they replace flange bolts of smaller size in which case they shall be fitted with a nut on each side of the pair of flanges.
K. The Contractor shall furnish and install all support necessary to hold the piping and appurtenances in a firm substantial manner at the lines and grades indicated on the drawings.
L. All fittings shall be backed up with concrete thrust blocks as indicated on the standard details. Where adequate backing cannot be obtained, suitable joint restraint shall be used. Megalugs or equivalent restraints shall be used on all new mains where pipe meets fittings.
M. Processed sand or 1/2 inch stone shall be used for bedding pipes and fittings. A depth of 6 inches of sand is required below pipes in a ledge or rock zone. Processed sand or stone bedding shall be placed to the full width of the trench and continue to an elevation of 12 inches above the top of the water main and fittings. Above this point backfill shall be suitable material from excavation, or if directed by the Water Department, it may be required to use bank run gravel containing no stones over 4 inches. This material shall be thoroughly compacted in 12-inch lifts to the top of the trench.
N. Minimum cover over water mains shall be 5 feet, maximum cover will be 7 feet unless approved or directed by the Water Department. All depth measurements shall be from the top of the piping being installed to the finished grade.
O. Except where otherwise directed, 2 feet minimum horizontal and vertical clearance shall be provided between the exterior or the water mains and other structures. Where a new main passes under or over utilities, it shall cross without use of bends.
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