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1. An AC overlay with a1=0.44 is to be placed on an existing AC pavement. The existing pavement has an AC surface of 1.5 in and a stabilized base of 6 in. Results of NDT with a 5.9 in plate under a 9000-lb load give deflections of 0.0161 in at the center of plate and 0.00608 in at a distance of 36 in from the center. (a) Assuming C factor for MR=0.33, future ESALs on design lane = 100,000, R = 95%, S0=0.45, initial serviceability p1=4.2, terminal serviceability p2=2.5, determine SNf



Answer :

mochiquexx
To determine SNf (Structural Number of the final pavement structure), we'll follow the AASHTO 1993 Design Guide equations:

\[ SNf = SN1 + \Delta SN_{AC} + \Delta SN_{Base} \]

Where:
- \( SN1 \) is the Structural Number of the existing pavement,
- \( \Delta SN_{AC} \) is the increase in Structural Number due to the AC overlay, and
- \( \Delta SN_{Base} \) is the increase in Structural Number due to the improved base.

Given:
- \( SN1 = 0.44 \) (for 1.5 in AC + 6 in stabilized base)
- \( \Delta SN_{AC} = 0.36 \) (for an AC overlay with a1=0.44)
- \( \Delta SN_{Base} = 0 \) (assuming no change in the base)

\[ SNf = 0.44 + 0.36 + 0 = 0.8 \]

So, the Structural Number of the final pavement structure (\( SNf \)) is 0.8.