Category:733 Precast Concrete Box Culverts
733.1 Construction Inspection for Sec 733
733.1.2 Subgrade Preparation and Bedding
The bottom slab of concrete box-type structures should be placed on reasonably dry foundation material of sufficient uniformity to prevent differential settlement of the structure. The foundation need be only sufficiently stable that the material does not become mixed with concrete as the bottom slab is being placed.
It is the contractor's responsibility to provide a satisfactory foundation except when foundation material at grade is inherently unsound. Inherently unsound material is material hich, even if properly drained, would prevent satisfactory installation of reinforcing steel and placement of concrete.
If the foundation consists of material which can be stabilized by draining, it is the contractor's responsibility to provide drainage. In some cases involving sandy material and high groundwater table, contractors have elected to install well point drainage systems. This is one way of providing a suitable foundation, but it is at the contractor's option.
Sometimes the contractor elects to undergrade a few inches and backfill with granular material to provide an easily maintained base on which to construct the culvert. This is a satisfactory procedure. Payment should not be authorized for removal or replacement of material in this situation, or when the foundation is unsuitable due to improper methods of construction.
Some material may have a high organic content or may be a soil which will not permit satisfactory construction of the bottom slab even when properly drained. When this situation exists authorization may be given to remove and replace material, with payment to be made in accordance with Sec 206.6.3.
Payment for stabilizing foundations should be authorized only after the contractor has provided adequate drainage to establish that material is unsuitable. Undergrading must be authorized by documentation record. If the contingent item of granular backfill is involved an approved change order is required before payment can be made.
733.2 Material Inspection and Laboratory Testing for Sec 733
