The determination of the grade for street resurfacing and reconstruction projects is limited by the amount of existing pavement that remains at, or close to, the original grade. In addition, except for increasing curb return radii, the existing curbs generally remain in place. Therefore, the existing top of curb grade as well as drainage are also limiting factors.
For partial resurfacing or reconstruction jobs, where the existing cross-sections are modified, usually no flow line grade change, or only a slight grade adjustment, is needed.
For total resurfacing or reconstruction, a new flow line grade may be established but will be limited as indicated above by the top of curb grade and drainage considerations. If a smooth flow line grade is developed and a uniform crown section is used, a smooth profile grade can be readily achieved.
E 564.1 In Meeting Existing Improvements
Where new grades are established, further study may be needed in meeting existing improvements that lie either between or within the intersections, and in providing drainage, particularly in flat areas.
E 564.11 Between Intersections
The drainage in flat areas may be improved by constructing an adequate pavement crown section and including concrete gutters. The concrete gutters should have an absolute minimum grade of 0.15 percent. If there is an existing gutter, it may have to be reconstructed to provide sufficient grade to drain.
Sufficient grade or “fall” between the high and low ends of the street may be achieved in the following manner:
- Assume the existing curb remains undisturbed and has a curb face of 8 inches. If the pavement flow line is raised 3 inches at the high end of the street, giving a 5-inch curb face, and the pavement flow line is lowered 1 inch at the low end of the street, giving a 9-inch curb face, the total overall “fall” of the street is increased a total of 4 inches. The values given in this example represent the desirable minimum and maximum heights of curb face.
- Where a drainage structure is located at the low end of the street, the warped gutter or local depression in the catch basin area is lowered as well as the approaching pavement flow line grade. If this is insufficient, it may be necessary, in addition to the above, to partially reconstruct and lower the existing catch basin, or to construct a new catch basin.
Changing of the street grade due to drainage problems or adjusting profile and cross-sections may require certain local grade adjustments to meet existing improvements. If these local grade adjustments cannot be made, the existing improvements must be remodeled, reset, or removed and replaced to meet the new grades. The facilities that are most generally encountered are driveways, roof drains, alley intersections, and manholes. The resetting of manholes is determined by other agencies, and the alley intersections are remodeled only up to a point deemed necessary to provide a smooth join. See Section E 510, Alleys.
A new grade should provide a 1-inch curb face for existing driveways but, where necessary, may vary between 0 inches and 2 inches. The pavement flow line should not cover more than one-quarter of the diameter of existing root drains. If these limits cannot be met by varying the flow line, it will be necessary to remove and reconstruct the roof drains and driveways to the new grade. Curbs and sidewalk removed for this purpose need be removed only up to the nearest joint immediately adjoining the reconstruction area.
When reconstructing longitudinal gutters, the standards for gutter hike-up must be met as indicated in Section E 641.111, Transverse Slopes. In some cases when standards are used, the existing surfacing adjoining the gutter may not form a smooth cross-section with the proposed edge or gutter. If by varying the outer edge of gutter within the prescribed limits, a smooth cross-section cannot be produced, a portion of the existing pavement may have to be removed or resurfaced. If the pavement adjoining the outer edge of gutter permits a smooth grade, but the pavement is broken, warped, or in unsatisfactory condition, sufficient pavement should be removed or resurfaced to produce a satisfactory cross-section. In any case, at least one foot of existing bituminous (asphalt) pavement adjoining a proposed new gutter should be removed to provide space for forming the gutter.
E 564.12 In Intersection Areas
In those projects where the intersection pavement remains, only that portion of pavement needs to be removed and reconstructed to make a smooth join and pavement profile line. Work may be required in the intersection where it is desired to increase the curb return radii (see Subsections E 633.3, Curb Return Radii, and E 392, Intersection Drainage) or to remove existing cross-gutters and replace with rideovers (see Subsections E 641.3, Cross-Gutters, and E 391.32, Rideovers), or where the work done between intersections does not permit a smooth join at the intersection.
In redesigning the intersection, the proposed grades should be plotted indicating the flow line, quarter line, and centerline of the street. These lines are produced across the intersection and the flow lines are also extended around the curb return. If the resulting riding lines and drainage are not satisfactory, it may be necessary to readjust the grades of the remodeled street as it enters the intersection, remove additional pavement from the legs of the intersecting streets, or both.
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