Resources

Subgrade Only

Step 1 — Convert CBR to Resilient Modulus

Assuming a subgrade with a CBR of 3, the subgrade resilient modulus is:

Step 2 — k-Effective Dynamic

With no subbase, En = Ê, there is 0 in. of subbase thickness, the soil's Poisson's Ratio is 0.40, and the effective dynamic k-value is:

Step 3 — Calibration Factor f

Again, with no subbase, En = Ê, there is 0 in. of subbase thickness, and the calibration factor is:

Step 4 — Dynamic and Static k

Dynamic k

130

psi/in.

Static k

65

psi/in.

Verify in the calculator by entering CBR = 3, clicking Apply to Subgrade, and clicking Calculate with no layers added.

One Subbase

Adding a 6-inch granular subbase with a modulus of 25,000 psi over the same CBR 3 subgrade with a Poisson's Ratio of 0.40.

Step 1 — Resilient Modulus (same as above)

Step 2 — Equivalent Modulus Ê

For a single subbase layer, Ê equals the layer modulus directly:

Step 3 — k-Effective Dynamic

With h = 6 in., En = 5,161 psi, Ê = 25,000 psi:

Step 4 — Calibration Factor f

Step 5 — Dynamic and Static k

Dynamic k

137

psi/in.

Static k

68

psi/in.

Verify in the calculator by entering CBR = 3, applying to subgrade, adding one layer at 25,000 psi and 6 in., and clicking Calculate.

Two Subbases

A 6-inch layer at 150,000 psi is added on top of the previous example, giving two subbase layers over the same CBR 3 subgrade.

Step 1 — Resilient Modulus (same as above)

Step 2 — Equivalent Modulus Ê

With two layers above the subgrade (E1 = 150,000 psi, h1 = 6 in.; E2 = 25,000 psi, h2 = 6 in.), the Odemark weighted mean uses E1 as the reference:

Step 3 — k-Effective Dynamic

Total h = 12 in., En = 5,161 psi, Ê = 69,866 psi:

Step 4 — Calibration Factor f

Step 5 — Dynamic and Static k

Dynamic k

176

psi/in.

Static k

88

psi/in.

Verify in the calculator by entering CBR = 3, applying to subgrade, then adding two layers: 150,000 psi / 6 in. on top and 25,000 psi / 6 in. below, and clicking Calculate.