3.3 Base Selection
Many factors are considered beyond material testing and acceptance in accordance with the characteristics identified in Item 247. Selection factors often considered are:
- availability and cost
- surface thickness
- subgrade stiffness and strength
- lateral confinement
- traffic volume and loading.
From these factors, a number of different selection matrices may be generated. The applicability of these factors may be weighed quite differently in each district.
An example of a decision matrix for the selection of base grades is contained in Table 3-8. Grades recommended in a chart similar to Table 3-8 should be chosen based on local experience and historical performance.
Shoulder Width | HMA Surface Thickness | Traffic (Design ESALs)1 | Base Grades |
---|---|---|---|
< 3 ft. | Surface Treatment | < 500,000 | 4* |
> 500,000 | 1-2 | ||
HMA < 3 in. | All traffic levels | 1-2 | |
HMA > 3 in. | < 500,000 | 4* | |
> 500,000 | 1-2 or 5 | ||
> 3 ft. | Surface Treatment | < 500,000 | 4* |
> 500,000 and < 3,000,000 | 1-2 or 5 | ||
> 3,000,000 | 1-2 | ||
HMA < 3 in. | < 500,000 | 4* | |
> 500,000 | 1-2 | ||
HMA >3 in. | < 500,000 | 4* | |
> 500,000 | 1-2 or 5 | ||
1 Percentage of trucks in addition to design ESALS should be taken into consideration.*Grade 1-2 requirements without minimum strengths. |