(a) Single Wheel, Single Axle
e
(b) Dual Wheels, Single Axle
e
l
= 1.8 to 2.0 m
(c) Dual Wheels, Tandem Axles
e
l
= 1.8 to 2.0 m
(d) Single Wheels, Tandem Axles
e
Figure 4. Wheel and axle configurations.
construction). Alternatively, the guidance pre-
where s is the shear strength of the soil, c is the
cohesion, p is the effective stress, and φ is the angle
+ t
sented in Appendix A, which was developed
more recently than that listed in TM5-818-8
of internal friction. For soft clay subgrades at or
(1995), can be used to select a geotextile.
near saturation, moving wheel loads are transient,
meaning that undrained loading applies. Thus, the
angle of internal friction is zero and the undrained
Theory
Bender and Barenberg (1978) summarize the
shear strength of the soil is equal to its cohesion.
theory and tests that led to the design method
Based on the theory of plastic equilibrium, the ul-
described above. Using the MohrCoulomb fail-
timate bearing capacity, qd, for soil in this condi-
ure criteria for soils, the shear strength is
tion is
qd = (2 + π)c .
s = c + p tan φ
(2)
(1)
4
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