FWD BackCalculation of Existing Pavement Structure

Pavement Structure

Critical Responses

Overlay Thickness Design (Critical Responses) Rutting—Vertical strain on top of the subgrade, within the unbound/bound base and AC layers Fatigue cracking—Horizontal strain at the bottom of AC layers Thermal cracking—Tensile stress at the surface of the AC layer

Structural Responses for AC/AC Overlays Critical structural responses are: –Tensile strain at the bottom of AC overlay –Tensile strain at the bottom of original AC layer –Vertical stress at the top of the subgrade

Structural Responses for AC/AC Overlays AC Overlay Existing AC Pavement  r Base Subgrade  v  r Bond Milling and Tack Coat

Structural Responses for AC/AC Overlays Other considerations: –Not all design procedures consider both strains at the bottom of the overlay and existing layer –Both strains should be examined as a minimum –If the existing layer is extensively cracked it may be modeled as a granular layer, thus consider only strains at the bottom of overlay

EverStress Input

EverStress Load & Evaluation Locations

EverStress Output

Pavement Deflection

EVERCALC General File

EVERCALC Deflection File Mil = 1/1000 inch

EVERCALC Output File

EVERCALC Summary File

EVERCALC General File

EVERCALC Output File