GC-4.2 - MANHOLES

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4.2.1 Scope of Work. The work shall consist of furnishing all materials, equipment, and labor necessary for the construction of manholes and accessories at the location and in accordance with the details of the plans and as specified herein. Manholes shall be of the precast-concrete or poured-in-place concrete type. Items not specifically mentioned, but necessary for completion of the work shall be considered as incidental to other items in the contract.


4.2.2 Materials.

4.2.2.1 Concrete for manhole bases, pipe encasement, or cradle shall conform to the requirements of Chapter VI of these specifications except that the slump shall be four (4) inches plus or minus one (1) inch.

4.2.2.2 Cast iron fittings and piping with mechanical joints shall be in accordance with USASI Specification A21, Class 50 and the plan details.

4.2.2.3 Cast iron frames and covers shall conform to the requirements of the Standard Drawing San-1.

4.2.2.4 Precast concrete manholes shall receive an application of asphaltic waterproofing paint on the exterior at the plant site.


4.2.3 Construction Methods.

4.2.3.1 If manholes are constructed of precast sections, each precast section shall be set in a preformed, bitumastic gasket material. A minimum of 6” bedding material shall be used under manhole base.

4.2.3.2 Inverts shall be precast or constructed with cement mortar after all precast sections are in place. Inverts shall be smoothly finished to assure smooth flow through the manhole with a minimum of two-tenths fall across the manhole and in accordance with the plans.

4.2.3.3 The elevation of manhole cover shall be adjusted to the required grade by shimming with concrete ring laid in a bitumastic material. Type “A” frame and covers shall be used in all areas.

4.2.3.4 Manholes shall be waterproofed on the exterior. Inlet and outlet pipes shall be joined to the manhole with a gasketed, flexible, watertight connection or any watertight connection arrangement that allows differential settlement of the pipe and manhole wall to take place.

4.2.3.5 Cold Weather Requirements. Whenever the temperature of the surrounding air is below 40 degrees F, or when the possibility exists that the temperature will fall below 40 degrees F within the 24-hour period after concrete operations, concrete placed in the forms shall have a temperature between 80 degrees F and 100 degrees F. All concrete shall be maintained at a temperature of not less than 50 degrees F for at least 72 hours, and shall be protected from freezing for at least an additional 72 hours or for as much time as is necessary to ensure proper curing of the concrete. The housing, covering, or other protection used in connection with curing shall remain in place and intact for at least 24 hours after the artificial heating is discounted. No dependence shall be placed on salt or other chemicals for the prevention of freezing. Contractor will be held responsible for any damage to concrete as a result of cold weather operations.

4.2.3.6 Finishing. The top surfaces of structures shall be struck off with a straight edge and finished with a wood float. Forms will be removed between 12 and 24 hours, and all exterior form ties shall be removed to a depth of one (1) inch below the surface. All fins caused by forms, joints, and other projections shall be removed, and all pockets cleaned and filled with mortar. All exposed surfaces shall then be wetted and hand rubbed with a rubber float using a sand and cement mixture to obtain a smooth and uniform texture as directed by the Engineer.

4.2.3.7 Curing. As soon after the completion of the specified finishing operations as the condition of the concrete will permit without danger of consequent damage thereto, all exposed surfaces shall either be covered with plastic sheet, or covered with earth and/or burlap, or when not required to be painted, sprayed with liquid conforming with ASTM designation C309.

4.2.3.8 Backfilling. Manholes, which lie within an area to be paved, shall be backfilled with granular material meeting the requirements for bedding materials specified hereinbefore. This material shall be placed and thoroughly compacted. All other manholes shall be backfilled with earth materials and shall be placed and jetted in the same manner as for sewer lines, specified hereinbefore.

4.2.3.9 Removal of Forms. Forms shall remain in place until, in the opinion of the Engineer, it is safe to remove them. In determining the time for removal of forms, consideration shall be given to the location and character of the structure, the weather, and other conditions influencing the setting of the concrete, and the requirements for curing and finishing.


4.2.4 Method of Measurement. Manholes exceeding eight (8) feet in depth will be measured to the nearest 1/10 foot.


4.2.5 Basis of Payment. Manholes up to six (6) feet in depth include all labor, equipment, materials, backfill, excavation, concrete base, cone, ring, and cover, and all fittings and appurtenances for sealing the manhole or construction drops associated with the manhole and acceptance testing, as well as the sidewalls, and will be paid for at the base price of each manhole complete in place. Additional payment will be made for any depth over six (6) feet at the unit bid price per vertical lineal foot. All excavation for manholes shall be included in the unit price per manhole. No direct payment will be made for furnishing and placing asphaltic paint, premolded, asphaltic filler, or other types of joint separators. The cost therefor shall be included in the price bid for the item of work of which they are a part.

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