TM 5-822-13/AFJMAN 32-1018
c. Thickness design. The thickness requirements for a plain concrete pavement on a modified soil foundation
will be designed as if the layer is unbound using the k value measured on top of the modified soil layer. For
stabilized soil layers, the treated layer will be considered to be a low-strength base pavement and the thickness
determined using the following modified partially bonded overlay pavement design equation:
(eq 7-1)
where
ho = thickness of plain concrete pavement overlay required over the stabilized layer, inches
hd = design thickness of equivalent single slab placed directly on foundation determined from layered
elastic method
Ef = flexural modulus of elasticity of the stabilized soil. The modulus value for bituminous stabilized
soils will be determined according to the procedures in appendix B of TM 5-822-5/AFM 88-7, Chap. 3.
The modulus value for lime and cement stabilized soils will be determined using equations in
appendix B of TM 5-822-5/AFM 88-7, Chap. 3
hS = thickness of stabilized layer, inches
7-4. Reinforced Concrete Pavements.
Figure 7-1 is a design chart for determining the thickness of reinforced concrete pavement based on the thick-
ness of the plain concrete pavement and the amount of steel to be used in the pavement. Figure 7-1 also shows
the maximum allowable length of reinforced concrete slab.
7-5. Design Examples.
a. The input information needed for the design are as listed in paragraph 2-2. Based on the trial pavement
sections, the critical stresses and strains are computed using the elastic layered computer codes. Damage from
each vehicle group is summed and the design thickness is determined when the cumulative damage is equal to one.
b. In the computation, the following values are used.
(1) The interface between the concrete slab and the subgrade soil is assumed to be frictionless and the
parameter equal to 10,000 is used in the computation.
(2) The moduli and Poisson's ratio of the PCC and the subgrade are 4,000,000 psi, 0.2, 10,000 psi, 0.4,
respectively.
(3) The tire contact pressure is assumed to be 70 psi. In tracked vehicle, the track width is constant and
the contact pressure varies with the gross load.
c. Example No. 1. This example is to show the procedures for determining the elastic modulus values of
unbound granular base and subbase courses from figure B-l.
(1) Assume a concrete pavement having a base course thickness of 4 inches and a subbase course thick-
ness of 8 inches over a subgrade having a modulus of 10,000 psi. Initially, the subgrade is assumed to be layer
n + 1 and the subbase course to be layer n. Entering figure B-l with a modulus of layer n + 1 of 10,000 psi and
using the 8-inch subbase course curve, the modulus of the subbase (layer n) is found to be 18,500 psi. In order to
determine the modulus value of the base course, the subbase course is now assumed to be layer (n + 1). Entering
figure B-l with a modulus of layer n + 1 of 18,500 psi and using the 4-inch base course curve, the modulus of the
base course is found to be 36,000 psi.
(2) If, in this example, the design thickness of the subbase course had been 12 inches, it would have been
necessary to divide this layer into two 6-inch-thick sublayers. Then, using the procedure above, the modulus
values determined for the lower and upper sublayers of the subbase course and for the base course are 17,500,
25,500, and 44,000 psi, respectively.
d. Example No. 2.
(1) As an example of the application of the design procedures given for nonstabilized foundations, deter-
mine thickness requirements for a plain concrete road to carry the following traffic:
Passenger cars
2,000 per lane
per
day
Panel and pickup trucks
1,300 per lane
per
day
Trucks, 2-axle
150 per lane
per
day
Trucks, 3-axle
50 per lane
per
day
For each type of vehicle, the operations per coverage ratios are obtained from table 5-1 and used to convert
operations to coverages according to axle configurations. The computed coverages for each axle type are tabu-
lated in table 7-1.
7-2
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