A.
The contractor shall not open more trench in advance of pipe laying than is necessary to expedite the work. One hundred feet shall be the maximum length of open trench permitted on any line under construction. Except where tunneling, jacking or boring is permitted by the Township or called for on the drawings, all trench excavation shall be open cut from the surface.
B.
The alignment and grade or elevation of each pipeline shall be fixed and determined by means of offset stakes or other approved methods. Vertical and horizontal alignment of pipes and the maximum joint deflection used in connection therewith shall be in conformity with the requirements of the specifications covering the installation of the pipe laid in each case.
C.
Trenches for force mains shall be carefully excavated so that the minimum cover over top of pipe will be 48 inches to existing street surface, or the future street surface when indicated, and so that the force main will slope continuously upward to point of discharge, to air release valves, if any, or to pump station. Greater cover at some locations along the line may be required due to street or ground profile and clearance of culverts, structures, utility lines, etc. Where force mains parallel gravity sewers, a separate trench may be dug, or a common trench may be dug providing a shelf of solid earth for the force main to rest on. When passing a manhole, the force main shall be bowed away from the manhole in a gentle arc not exceeding allowable deflection limits in accordance with manufacturer's recommendations or industry standards, whichever is more stringent.
D.
Trenches shall be excavated to a width which will provide adequate working space and pipe clearance for proper installation, jointing and embedment. The minimum permissible trench widths and clearances between the installed pipe and either trench wall shall be as follows:
Pipe Size (inches) | Minimum Trench Width (inches) | Minimum Side Wall Clearance (inches) | |
|---|---|---|---|
6 or less | 20 | 6 | |
8 | 22 | 6 | |
10 | 24 | 6 | |
12 | 26 | 6 | |
14 | 29 | 6 | |
16 | 32 | 6 | |
18 | 35 | 6 |
The stipulated minimum clearances are not minimum average clearances, but are minimum clear distances which will be permitted between any part of the pipe as laid and any part, projection or point of rock, shale, stone or boulder. |
E.
The maximum permissible trench widths below an elevation six inches above the top of the installed pipe shall not exceed the safe limit for the strength of pipe and class of bedding used. If so directed, the contractor shall provide evidence to the satisfaction of the Township Inspector that pipe strength is not exceeded relative to height of fill above the pipe, trench width and bedding class.
F.
The maximum trench width for cast-iron pipe and ductile iron pipe shall not exceed the outside diameter of the pipe plus 24 inches. Where necessary to reduce the earth load on trench banks to prevent sliding and caving, the banks may be cut back on slopes which shall not extend lower than one foot above the top of the pipe, subject to the limitations above.
G.
Unauthorized trench widths. Where, for any reason, the width of the lower portion of the trench as excavated at any point exceeds the maximum permitted in the foregoing tables, either pipe of adequate strength, special pipe embedment or Class A concrete arch encasement, as required by loading conditions and as determined by the Township, shall be furnished and installed by and at the expense of the contractor.
H.
The use of mechanical equipment will not be permitted in locations where its operation would cause damage to buildings, culverts or other existing property, utilities or structures above or below ground; in all such locations, hand excavating tools and methods shall be used.
I.
Mechanical equipment used for trench excavation shall be of a type, design and construction and shall be so operated that the rough trench excavation bottom elevation can be controlled, that uniform trench widths and vertical side walls are obtained at least from an elevation one foot above the top of the installed pipe to the bottom of the trench, and that the trench alignment is such that the pipe, when accurately laid to specified alignment, will be centered in the trench with adequate clearance between the pipe and side walls of the trench. Undercutting of the trench side wall to obtain clearance will not be permitted.
J.
Cuts in concrete pavement and concrete base pavement shall be no larger than necessary to provide adequate working space for proper installation of pipe, pipe line appurtenances and paving replacement. Cutting shall be started with a groove at least 1 1/2 inches deep along each side of the trench and along the perimeter of cuts for structures.
K.
Concrete pavement and concrete base pavement over trenches excavated for pipe lines shall be removed so that a shoulder no less than 12 inches in width at any point is maintained between the cut edge of the pavement and the top edge of the trench. Pavement cuts shall be made to and between straight or accurately marked curved lines which, unless otherwise required, shall be parallel to the center line of the trench.
L.
Bituminous pavement over trenches shall be removed so that a shoulder not less than 18 inches in width at any point is left between the cut edge of the pavement surface and the top edge of the trench. A minimum of 12 inches in width of base material shall be removed from the edge of the trench to subgrade.
M.
Pavement restoration or temporary restoration shall comply with the standard details of the contract drawings.
N.
Except where otherwise required, pipe trenches shall be excavated below pipe subgrade elevations to provide for the installation of granular fill pipe foundation material.
(1)
Bell holes. Bell holes shall provide adequate clearance for the tools and methods used in installing the pipe. No part of any bell or coupling shall be in contact with the trench bottom, trench walls or the granular fill when the pipe is jointed.