1. (12pts) The figure below is an existing pavement system for interstate highwa
ID: 1714134 • Letter: 1
Question
1. (12pts) The figure below is an existing pavement system for interstate highway with moduli and drainage coefficients as shown. Given R. 95% So-0.30, the current (initial) serviceability (PSI)i-3.2 and terminal serviceability (PSI)t- 2.2. If the thickness of theP la is 12 inch, determine the ESALs for the remaining life of the rigid pavement using the AASHTO 1993 design charts. Detail all the STEPS of the design procedure using charts 18k SAL PCC Slab-Elastic Modulus - 5 x 10* psi, Road bed Modulus of Subgrade reaction -200 pci, Modulus of Rapture 600 psi Drainage Coefficient = 0.8 I nad Transfer Coefficient Solution: 2. (8pts) For the above pavem allowa shoulders. ent system use the PCA method to determine the 18-kip SAL ble number of load repetitions for both Fatigue and Erosion failures. Assume no concrete Solution:Explanation / Answer
For question number 1
AASHTO equation for EASL
Log ( W18 ) = Zr x So + 7.35 log ( D+1) -0.06 + log (DPSI/3)/( 1+ ((16240000/(D+1)^8.46))+ (4.22+0.32Pt)log ((Sc Cd (D^0.75 -1.132)/(215.63J( D^0.75 - (18.42/ (Ec / K)^0.25)))
Where W18 is EASL ; Zr is standard normal deviate; So is standard deviation; D is pavement thickness in inches ; DPSI is difference in pavement serviceability index for beginning and terminal; Sc is modulus of rupture and K is subgrade modulus
Thus log ( W18) = 6.8027
Thus EASL = 10^6.8027= 6348922.133
For question number 2 PCA method to be used
For no concrete shoulder and K= 200 pci and pavement thickness of 12 inches equivalent stress = 137 psi
Therefore stress ratio = 137/ 600 = 0.228 <0.45
Thus no. of cyclic repetitions as per fatigue criteria is infinite
No. of cyclic repetitions as per erosion criteria
Erosion factor as per PCA table for no dowel no concrete shoulder = 2.53
Interpolating from graph we get allowable load repititions as per erosion criteria > 100,000,000
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