Section 7 2. Installation
SECTION 7 SANITARY SEWER GRAVITY COLLECTION SYSTEM
A. Proper and suitable tools and equipment for the safe and convenient handling and laying of pipe shall be used, conforming to manufacturer’s recommendations. At the time of lying, the pipe shall be examined carefully for defects, and should any pipe discovered to be defective after being laid, it shall be removed and replaced with sound pipe by the Contractor at his expense.
B. Excavation and backfill for trenches and manholes shall be specified in the Sitework Excavation and Backfill for Utilities and Structures Section, of the CMB Public Works Manual.
C. Where location of sewer is not clearly defined, install the sewer so it shall not be closer than 6 feet horizontally, pipe face to face (10 ft. preferable) with a water supply main or service line. When the bottom of the water pipe will be at least 18 inches above the top of the sewer pipe, the horizontal spacing may be a minimum of 6 feet separation, pipe face to pipe face (see section (IV)( A) (4) for pipe material to be used).
D. Trench widths in stable soils shall provide a 12-inch maximum clearance on each side, between the outside of the pipe barrel and the face of the excavation, or sheeting if used, when measured to a point 12 inches above the top of the pipe. Minimum trench widths under the same conditions shall be minimum 6-inches on each side. Minimum trench widths are required to provide room for a man to place and compact the haunches and initial backfill material. In unstable soils (defined as peat, mulch or other organic soils, elastic silts and clay or fine sands below the water table), trench widths shall be a minimum of five (5) nominal pipe diameters in width when measured at a point 12-inches above the top of the pipe to accommodate trenching and compacting equipment and requirements.
E. Bedding and initial backfill 6 inches below and 12 inches above sewer mains and services shall be coarse sand with no rocks larger than ¾ inch diameter.
F. Shape the bottom of the trench by hand to give substantially uniform circumferential support to the bottom of each pipe. When applicable, pipe laying shall proceed upslope with the spigot ends pointing in the direction of the flow.
G. The pipe shall be laid in the prepared trench, true to line and grade. The pipe barrel shall receive continuous, uniform support with no pressure being exerted on the pipe joints from the trench bottom.
H. A “Green” plastic detector tape with metallic foil and with the words “CAUTION SEWER LINE BURIED BELOW” printed at 30″ intervals along the tape, shall be placed 18″ above all sewer mains and laterals.
I. Each pipe to be laid true to line and grade as indicated on the drawings and in such manner as to form a close concentric joint with the adjoining pipe and to prevent sudden offsets of the flow line. The pipe shall be laid so that the identification markings are located on the top of the installed pipelines The Contractor shall use surveying instruments to maintain alignment and grade. At least one elevation shot shall be taken on every pipe joint.
J. The interior of the sewer pipes shall be kept clean and free of all dirt and superfluous materials. Where cleaning after laying is difficult because of small pipe size, a suitable swab or drag shall be kept in the pipe and pulled forward past each joint immediately after the joining is completed. During suspension of work for any reason at any time, a suitable stopper shall be placed in the end of the pipe last laid to prevent mud or other foreign material from entering the pipe. Adequate support shall be provided in this case to retain pipe in place against uplift due to water in trench. Any pipe found defective shall be immediately removed and replaced with sound pipe.
K. Sewer pipes shall be installed in accordance with latest revision of ASTM D2321 and the Uni-Bell Plastic Pipe Association’s “Recommended Practice for the Installation of PVC Sewer Pipe”.
L. Manholes shall be constructed as indicated on drawings in accordance with the City of Miami Beach Standard Details. Manhole pipe openings are to be sealed with elastomeric grout or approved equal. No molding plaster will be allowed.
M. The invert channels shall be formed of brick or brick rubble thoroughly bedded and covered with sand-cement grout, accurately shaped to a semicircular bottom conforming to the inside of the adjacent sewer section. Steep slopes outside the invert channels shall be avoided. Changes in size and grade shall be made gradually and evenly. Changes in the direction of the sewer or entering branch shall be a smooth curve with radius as long as practical.
N. After the manholes have been installed and inspected by the City for cracks and defects, two (2) coats (a minimum thickness of 8 mils each dry of protective material, Kopper’s 300M or equal) shall be applied to the inside surface of the manhole at the job site. This material shall be applied in accordance with the manufacturer’s specifications and cover all voids. The coats shall have contrasting colors so as to be easily verified.
O. Manhole to sewer main connections:
1. PVC sewers: The first joint at both influent and effluent sewers at each manhole, including service laterals, shall consist of an approved manhole coupling grouted into the manhole wall, and providing a continuous watertight elastomeric gasket seal between the coupling and the pipe inserted therein. The coupling shall have an increasing tapered interior from the gasket groove to allow flexibility for the pipe in the event of future settlement of the manhole or pipeline. The first length of PVC pipe into or out of the manhole shall be two (2) feet long, maximum, and shall be either plain-end by plain-end, or plain-end by bell. In the first option, the next joint shall be a double bell PVC repair coupling (no stop) with a maximum one (1) inch gap between the pipes inserted therein. In the latter option, the next joint shall be another two (2) feet long section maximum, of plain-end by bell PVC pipe.
2. Ductile Iron Pipes: The first length of pipe into or out of the manhole shall be a 2-foot length of plain end by plain end ductile iron pipe (i.e. two (2) feet, as measured from the outside wall) grouted directly into the opening in the manhole wall. This Plain End to Plain End short sleeve shall be joined to the spigot end of an adjacent ductile iron or to the Vitrified Clay Pipe with a Fernco Adapter.
3. Vitrified Clay Pipes (VCP) : shall be removed and replaced with either PVC or DI pipe. New pipes are to be connected to the existing VCP by appropriate Fernco adapters.
4. Where a service lateral enters a manhole at an elevation of two (2) feet or less, an internal drop shall be provided. For drops over two (2) feet above the sewer main invert, a drop connection on the exterior, with a cleanout extension into the manhole shall be provided. No brick manholes are allowed with outside drops.
P. Frames and Covers: Cast iron frames and covers shall be set in a bed of mortar and carefully adjusted to elevation shown on the drawings. A minimum of 3 and maximum of 5 courses of brick shall be provided under frames for adjusting manhole cover elevations. Interior shall be sealed as specified above for the manholes.