1. All structures shall consist of straight pre-cast reinforced riser sections, a top eccentric conical section and a monolithic base section, except that a flat top section shall be used whose shallow cover requires a top section less than 4 feet. Base section shall allow for a 4 foot sump depth. 2. Pre-cast structures shall be manufactured with a minimum compressive strength for the concrete of 4,000 PSI on a 28 Day Test. The circumferential steel reinforcement for riser sections and base walls shall be 0.12 square inch per lineal foot (both ways). Reinforcing in the bottoms of bases shall be of the same design. Precast concrete barrel sections with precast top slabs and transition sections shall be designed for a minimum of H-20 design loading per AASHTO HS-20-44; ASTM C478 Spec for “Precast Reinforced Concrete Manhole Sections.” 3. Each section of the pre-cast manhole shall have two holes for the purpose of handling and laying. 4. Each Barrel section shall have tongue and groove joints.
