CHAPTER  1400. Sewer Manholes.

 

 1401.  General. The contractor shall furnish and install watertight pre-cast concrete manholes at the locations shown on the drawings approved by the Engineer.  Manholes shall be furnished complete with cast iron rings and covers.

 

 1402.  Concrete Bases. Manhole bases shall be of concrete conforming to the requirements of these specifications. Where sewer lines enter manholes, the invert channels shall be smooth and semi‑circular in cross section.  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 smooth and slope toward the channel at not less than one‑half inch per foot.

 

 1403.  Pre-cast Concrete Manhole Sections. All precuts sections including riser sections, cones, grade rings, and flat slab tops, shall conform to ASTM Specification C478 and a minimum dimension of 48".  Cones shall be eccentric.  Grade rings shall be a standard product, manufactured particularly for use in manhole construction and sized to fit the cones on which they are to be placed.  Wall thickness shall be not less than that of the cone.  Grade rings shall be not less than two inches (2") high, nor more than six inches (6") high.  All pre-cast components shall have tongue and groove ends.

 

 1404. Placing Pre-cast Manhole Sections. The walls shall be constructed true to line and grade as established by the Engineer.  A butyl gasket shall be placed on the groove of the lower section pipe prior to placing the next section of pipe. The entire joint shall then be completely filled with mortar and troweled to a smooth finish on both the inside and the outside.

 

 1405. Drop or Connecting Manholes. Drop manholes, wherever shown on the plans, shall conform in all respects to the requirements for standard manholes of the type or types used in the project, except for the additional drop detail as shown on the detail plans.

 

 1406. Covers and Frames. The size and shape shall be as detailed on the plans.  Manhole covers and frames with fiberglass or aluminum trash catches shall be of cast iron conforming to the minimum requirements of ASTM Designation A‑48‑46 Class #30 and be 400 pounds minimum weight.  Manhole covers shall be vented. Bearing surfaces shall be machined to flat, plane surfaces which provide for full contact between frame and cover.  Any cover which tends to rock or tip will be rejected.  All covers shall display word "SEWER'.

 

 1407. Steps. All manholes shall be provided with steps.  The steps shall be 1/2 inch grade 60 steel encapsulated in polypropylene. The steps shall conform to ASTM C‑478.  The steps shall be placed in the manholes at the time that the sections are cast.  No leakage at steps will be permitted.