Minimum fill height for ALL types of pipe is 12 inches as measured from the top of the pipe to the top of soil backfill, excluding any prepared stone base or pavement, unless otherwise shown on the plans, drawings, or fill height tables as referenced below.
During construction of pipe culverts, there are also requirements to be met for fill heights in respect to the construction equipment being operated over the culverts prior to completion of the finished grade.
Maximum fill height requirements for pipe culverts are dependent on both pipe material type and type of installation.
A. DRIVEWAY TYPE DEFINITIONS FOR MAINTENANCE
Due to the site specific aspects of driveway installation for NCDOT Maintenance forces, definitions must be made of what types of driveways may be encountered. The following classifications are as set forth by the "NCDOT Policy on Street and Driveway Access to North Carolina Highways
". These definitions also apply to subdivision roads that may receive future acceptance onto the North Carolina Highway System.
Facilities meeting the following definitions fall under the approval control of the Department's local District Engineer.
A driveway connecting to a State-maintained street or highway to provide entrance to and/or exit from a private residential dwelling for exclusive use and benefit of those residing within. This type of driveway is normally installed by NCDOT maintenance forces when pipe is furnished by others.
2. Residential Subdivision
A driveway connecting to a State-maintained street or highway to provide entrance to and/or exit from residential subdivisions, apartment complexes, mobile home parks, and condominiums.
A driveway serving a commercial establishment, industry, governmental or educational institution, business, public establishment, or other comparable traffic generator. (This classification includes single family residential streets, where required by the District Engineer)
B. MINIMUM COVER REQUIREMENTS FOR DRIVEWAYS
Minimum cover requirements for driveways are the same for all pipe material types, unless used for Commercial Driveways. The following minimum cover requirements should be applied by the District Engineer for driveways as defined in Section A above:
Minimum Cover Required|
(excluding any pavement used)
(excluding any pavement used)
NCDOT Roadway Design Manual|
NOTE: Due to site-specific conditions, some driveways may not be able to get minimum cover. In these situations, every effort should be made to achieve minimum cover and any deviations from the minimum requirements will require prior approval from the responsible NCDOT Engineer.
C. MINIMUM COVER FOR CONSTRUCTION EQUIPMENT LOADINGS
The Specifications require that no heavy equipment shall be allowed to operate over any pipe culvert until the backfill is completed to at least three (3) feet above the top of the pipe. This depth may be increased if, in the opinion of the Engineer, the Contractor's equipment would cause damage to the completed pipe culvert. In any event, however, it is the Contractor's responsibility to conduct his operations in such a manner as not to cause damage to any completed structure. Where possible, NCDOT personnel shall periodically inspect completed pipe culverts for possible damage caused by live loads developed from the construction operations. This minimum cover must be maintained until heavy equipment usage is discontinued and the Contractor is prepared to set the final grade.
D. MAXIMUM COVER FOR FINISHED GRADE
Appendix B of this Manual shows the maximum cover allowed above the pipe culvert once the proposed finished grade has been completed. These tables should be adhered to in order to decrease the effects of the dead loads imposed on the pipe by the soil envelope above. This data is dependent on pipe material used, class of pipe used, wall thickness, area of reinforcing steel, concrete strength, corrugation pattern, and thickness of material used.