Material

Confining Pressure

(PSI)

Regression Equation

Coefficient of

Determination

Standard Error of Estimate

Single variable regression equations

Sand

5

10

15

σd = 41.3 − 12.8 PR

σd = 100.4 − 23.4 PR

σd = 149.6 − 12.7 PR

0.998

0.998

0.978

0.3

0.5

0.9

Sandy

gravel

5

10

15

σd = 51.3 − 13.6 PR

σd = 62.9 − 3.6 PR

σd = 90.7 − 5.8 PR

0.992

0.997

0.975

1.9

0.3

1.5

Multiple linear variable regression equations

Dense

Graded

Materials

5

10

15

σd = 2777 − 105.7 PR − 18.0 e + 1.6 γ − 1575 Cu

σd = 4474 − 148.7 PR − 29.1 e + 1.8 γ − 2411 Cu

σd = 5392 − 179.9 PR – 34.8 e + 2.2 γ −2983 Cu

0.859

0.893

0.941

18.1

22.7

21.2