Pavement Design
The development area appears to be just beyond the City of Fountain city limits in El Paso County. Presuming the development will be annexed into the City of Fountain, the governing specification for roadway design will be The City of Colorado Springs Engineering Criteria Manual (if the development remains in the County, the El Paso County Engineering Manual will govern; the two documents produce similar pavement designs).
The following information is provided for general consideration and applicable to residential roadways serving the subdivision, commercial roadways providing access to the subdivision, and commercial parking pavements. Final pavement designs will be required for jurisdictional acceptance, and are typically performed with soil samples obtained from roadway areas after the deepest public utilities have been installed. Typical pavement sections based upon RMG’s experience with the soils encountered on this site are presented below.
The silty sand encountered in the Test Borings will form the subgrade of pavement sections, and its stability and strength are critical to pavement design. The soil consists of well-graded silty sand. This material will typically classify as A-1 or A-2 soils in accordance with the American Association of State Highway and Transportation Officials (AASHTO) classification system. These soils are considered “excellent to good” as subgrade material.
The California Bearing Ratio, CBR, is an indication of the mechanical strength of pavement subgrades and is a key factor in determining pavement section thicknesses. A-1 and A-2 soils will typically produce CBR’s of 10 or higher. At these values the minimum pavement sections prescribed in the Engineering Criteria Manuals will be sufficient for expected traffic loading in the proposed developments.
Pavement Thickness
Assuming an adequate subgrade CBR, typical pavement sections for residential roadways, paved parking areas, and for heavy vehicle loading areas are presented below, where HMA is Hot Mix Asphalt, and ABC is Aggregated Base Course.
Typical Hot-Mix Asphalt Pavement Section
| Traffic Level | HMA over ABC (inches) |
|---|---|
| Moderate Traffic / Some Trucks | 4.0 / 6.0 |
| Heavy Vehicles with Turning Motions | 6.0 / 6.0 |
As an alternative to the HMA section above, Rigid Concrete Pavements are often employed in areas where heavy vehicle loading is expected. These areas include drop-off/pick-up areas, loading docks, trash pick-up areas, and other locations where heavy trucks will be making frequent turning and braking movements. Rigid pavements may be constructed directly on proof-rolled non-expansive granular subgrade, the top one foot of which has been compacted to a minimum of 95% of maximum dry density as determined by ASTM D1557.
Typical Rigid Concrete Pavement Section
| Traffic Level | Portland Cement Concrete (in.) |
|---|---|
| Heavy Vehicles with Turning Motions | 5.0 in. |
This pavement information is for preliminary planning purposes only. CBR values will be based on the materials encountered at the time of development and will be dependent upon the soil material used for site fill and subgrade construction. We suggest evaluating the soil conditions after site grading and pavement layout to perform a proper design.