§ 15.01.610. Manholes.

A.

General requirements. The contractor shall furnish and install watertight cast-in-place or precast concrete manholes at the locations shown on the drawings approved by the city engineer. Manholes shall be furnished complete with cast iron rings and covers. Manholes placed on longitudinal slopes greater than five percent, require "Precision Cover Systems, Inc." manhole risers and lids. Manhole spacing shall not exceed four hundred lineal feet unless otherwise approved by the city engineer. All manholes and mainline cleanouts shall be accessible with a mechanical pump truck for scheduled maintenance by the city.

B.

Foundation preparation. Dewatering of the site shall conform to the requirements for sewer trench dewatering in these specifications. Adequate foundation for all manhole structures shall be obtained by removal and replacement of unsuitable material with stabilization material; or by tightening with coarse ballast rock, or by such other means as provided for foundation preparation of the connected sewers, or as required by the city engineer. Where water is encountered at the site, all cast in place bases shall be placed on a one-piece waterproof membrane, so placed as to prevent any movement of the water into the fresh concrete. Precast base sections shall be placed on a well graded granular bedding course conforming to the requirements for sewer bedding but not less than eight inches in thickness and extending either to the limits of the excavation or to a minimum of twelve inches outside the outside limits of the base section. In the latter case, the balance of the excavated area shall be filled with select material well tamped to the level of the top of the bedding to positively prevent any lateral movement of the bedding when the weight of the manhole is placed upon it. The bedding coarse shall be firmly tamped and made smooth and level to assure uniform contact and support of the precast elements.

C.

Bases. All manhole bases shall be pre-cast and shall have pipe inverts and a resilient connection between pipe and manhole for each pipe connecting to the manhole unless otherwise noted and approved by city engineer. The rubber gasket boot PSX Series Six, or approved equal, shall be installed outside of the manhole and shrink-proof grout pipe connection will be put on the inside of the manhole. Cast-in-place bases shall be at least nine inches in thickness and shall extend at least six inches radially outside of the outside dimension of the manhole section. Precast bases shall be a minimum of nine inches in thickness. Concrete bases shall be placed upon a minimum of six inches of compacted one-inch minus gravel.

The concrete base shall be constructed so the first section of the precast manhole has a uniform bearing throughout the full circumference of the manhole wall. Sufficient mortar shall be deposited on the concrete base to provide a water tight seal between the base and the manhole wall. Concrete used in the construction of the base shall conform to six and one-half bag, four thousand psi concrete as specified in the concrete section of these specifications.

Where sewer lines pass through or enter manholes, the invert channels shall be smooth and semi-circular in cross section conforming to the details shown on the drawing, incorporating a four-tenths-foot drop through the manhole. Changes of direction of flow within the manholes shall be made with a smooth curve with as long a radius as possible. The floor of the manhole outside the flow channels shall be made with a smooth curve with as long a radius as possible. The floor of the manhole outside the flow channels shall be smooth and slope toward the channel at not less than one inch per foot.

Concrete pipe connections to manholes shall be achieved by use of manhole coupling adapters, rubber gaskets (ASTM C923 specifications), positive seal gasket system, or grouting a bell or spigot pipe at the appropriate location.

Upon written approval of the City Engineer, connecting boots may be used consisting of neoprene compound meeting ASTM C-443 specifications. The boot shall have a wall thickness of three-eighths-inch. The boot shall either be "cast-in-place" in the precast base or attached to the precast base by means of an internal expanding band. When the boot is attached to the precast base, a watertight seal between the boot and the precast base must be accomplished. An external band shall be supplied and used to clamp and seal the boot to the pipe. The band shall be made of 300 series non-magnetic corrosion-resistant steel. After the band has been placed, it shall be completely coated with a bituminous material approved by the city engineer.

The maximum size pipe that can be used in a forty-eight-inch manhole is PVC at fifteen-inch or concrete twelve-inch; all others shall be sixty-inch inside diameter. All manholes with three or more pipes entering the base shall be sixty-inch inside diameter.

All concrete for manhole bases shall comply with city approved specifications.

D.

Wall and cone sections. All manholes shall be precast, sectional, reinforced concrete pipe of either forty-eight-inch or sixty-inch inside diameter as specified. Both cylindrical and taper sections shall conform to all requirements of ASTM Designation C-76 for reinforced concrete culvert pipe with the following exceptions:

1.

The throat section of the manhole shall be adjustable, by use of pipe sections up to forty-eight inches in height.

2.

The taper section shall be a maximum of thirty-six inches in height, for forty-eight-inch diameter manholes and thirty-nine inches in height for sixty-inch diameter manholes, shall be of eccentric conical design, and shall taper uniformly to thirty inches inside diameter.

3.

The pipe used in the base section shall be furnished in section lengths of one, two, three and four feet as required.

4.

Reinforcing steel shall consist of a circular cage with a minimum cross sectional area of three-tenths of a square inch of steel per foot in both directions.

All joint surfaces of precast sections and the face of the manhole base shall be thoroughly cleaned and wet prior to setting precast sections. All joints, including grade rings, shall be set in butyl rubber gasket that is permanently flexible and non-shrinking. All joints shall be water tight and free from appreciable irregularities in the interior wall surface.

E.

Pipe connections. All pipes entering or leaving the manhole shall be placed on firmly compacted bedding, particularly within the area of the manhole excavation, which normally is deeper than that of the sewer trench. Special care shall be taken to see that the openings through which pipes enter the structure are completely and firmly rammed full of mortar to ensure water tightness.

F.

Backfill. Backfill around the manhole and extending at least one pipe length into each trench shall be hand placed and hand tamped with select material up to an elevation of one foot above the top of each pipe, regardless of the specifications for backfilling the sewer trenches adjacent thereto. The balance of the backfill shall conform to the requirements for trench backfilling.

G.

Covers and frames. All iron castings shall conform to the requirements of ASTM A 48 (Class 30) for grey iron castings. Rings and covers shall be thirty inches in diameter with machined bearing surfaces and with minimum cover weight of one hundred fifty pounds and minimum ring weight of two hundred thirty-three pounds. Any cover which tends to rock or tip will be rejected. In addition to the foundry name and year of manufacture, the cover shall be marked "SEWER" or "STORM DRAIN" as appropriate.

All manhole rings shall be carefully set to the grade shown on the approved drawings or as directed by the city engineer. The manhole covers shall be so installed to match the street profile. Where work is in paved streets, not less than six inches or more than eighteen inches shall be provided between the top of the cone or slab and the underside of the manhole casting ring for adjustment of the casting ring to street grade.

H.

Manhole steps. No steps shall be incorporated in manhole sections. All pre-fabricated holes for steps shall be filled in with shrink-proof grout.

(Ord. No. 2007-07-31, §§ 6.10—6.10.8, 7-10-2007; Ord. No. 2010-11-24, § 2, 11-23-2010)