Precast concrete manhole sections bear upon a cast-in-place base resting on eight inches of Class 2 aggregate base or one and one-half inches of drain rock for bay mud. The structure features a concentric cone top reducer, a concrete collar, and a two-inch pavement finish around the manhole frame and cover. Reinforcing steel consists of number five bars placed at twelve inches each way within the base and wall sections, supplemented by additional number five bars at pipe openings. A dimension table provides sizing parameters for pipe diameters ranging from twenty-four to forty-eight inches. Joints are sealed watertight with neoprene gaskets or ram-neck.
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