Category:731 Precast Reinforced Concrete Manholes and Drop Inlets

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731.1 Design

All concrete drop inlets in the standard plans and specifications are precast. Contractors are permitted to substitute cast in place drop inlets to the dimensions required for precast drop inlets. If special conditions require specifying cast in place concrete drop inlets, such as retrofit projects, special sheets are available by contacting Engineering Policy in the Design Division. Details for each type of precast drop inlet are shown in the standard plans.

731.1.1 Measurement for Payment

Measurement of precast concrete drop inlets, complete in place, will be measured to the nearest 1 ft. for the depth of the drop inlet. Depth is defined as the vertical distance from the uppermost precast section to the invert flowline as shown on the standard plan. Grates and bearing plates or curved vane grates and frames are paid for as separate items.

731.1.2 Type T Drop Inlets

Where two or more units of Type T drop inlets are required, measurement for payment will be the number of units times the depth, i.e., three units at 6 ft. depth, the pay quantity being 18 ft.

731.1.3 Quantity Sheet Procedure (Column Headings)

The suggested column headings for the accepted arrangement on the quantity sheet is as follows:

  • Col. 1 Station
  • Col. 2 Location
  • Col. 3 Type - A, B, C etc.
  • Col. 4 Depth "D" - As detailed in culvert sections. Depth is rounded to the nearest foot for each inlet for payment listed under appropriate size, i.e., "D" of 3.5 ft. would be 4.0 ft., "D" of 3.3 ft. would be 3.0 ft.
  • Col. 5 Grates and Bearing Plates or Curved Vane Grates and Frames from Standard Plan 614.10 or Standard Plan 614.11 by size of opening.
  • Col. 6 Class 3 Excavation
  • Col. 7 Remarks - Number and size of pipe openings required, etc.

731.2 Construction Inspection for Sec 731

These items are usually cast at a manufacturing plant and inspected by Division of Construction and Materials. Sometimes contractors elect to do their own precasting. If they do, the work should be inspected in accordance with applicable portions of Sec 1033, 1055, 1057, and 1066.

Final measurements are not required except for authorized changes which should be added to or deducted from plan quantity. The inspector should record enough information in a field book to show how the unit was built and this entry should be signed by the inspector.

731.3 Material Inspection and Laboratory Inspection for Sec 731

See Precast Drainage Units.