Question

A Portland Cement Concrete (rigid) pavement is to be designed using AASHTO empirical design method. The pavement should have an 8" granular sub-base having elastic modulus (E_sb) of 50x10³ psi. The resilient modulus of the subgrade is 5000 psi, and lying just 5 feet above rock strata (bed rock).

(a) Determine the design k value, assuming loss of support factor (LSF) of 2.

(b) Use the k value obtained from (a) to determine the thickness of the rigid pavement.  

Assume concrete elastic modulus (E_c) = 5 x 10⁶ psi , Modulus of rupture (Sc) = 650 psi, load transfer factor J = 3.2, drainage coefficient C_d = 1.0, present serviceability loss ∆PSI = 4.2 — 2.5 = 1.7, reliability R = 95%, standard deviation S_o = 0.29, and total ESAL W₁₈ = 5.1 x 10⁶.

Answer 1

Given

Subbase Elastic modulus Esb=50*103psi

Soil Resilient Modulus MR=5000psi

Subbase thickness Dsb=8in

According to AASHTO, guide for design of pavement structure 1993

Figure 3.3

Compositivte modulus of subgrade reaction = 400pci

Loss os subbase support =2(given)

According to AASHTO , guide for design of pavement structure 1993

Figure 3.6

modulus of subgrade reaction = 400pci

effective modulus of subgrade reaction k (for lSF=2) =40pci

given,

18 kip equivalent single axle loads (ESALs) =5.1*106

For 95% reliability standard normal deviate ZR =-1.645

standard deviation S0= 0.29

allowable serviceability loss ΔPSI=4.2-2.5=1.7

Pt=4.2

load transfer coefficient.j=3.2

modulus of subgrade reaction (pci)=40pci

drainage coefficient Cd=1.0

PCC modulus of rupture (psi)=650psi

slab thickness (inches) required=D

solving to nearest half-inch D=7inch

the thickness of the rigid pavement d=7 in