Environmental Engineering Reference
In-Depth Information
Loading
machine
frame
Proving
ring
Screw
jack
FIGURE 3.64
Laboratory CBR loading device (electric motor is
often used to drive jack at a rate of 0.05
in./min).
used) while the penetration resistance is recorded. The CBR is determined as the ratio of
the test resistance at 0.1 in. penetration to the standard resistance of crushed stone at the
same penetration (1000 psi or 70.3 tsf) (Asphalt Institute, 1969).
Field Test Procedure (ASTM D4429-93)
The plunger is jacked against the reaction of a truck weight. The test should not be per-
formed during the dry season because resistances will be higher than those to be relied
upon for pavement support. Field values are usually lower than laboratory values, prob-
ably because of the effect of confinement in the lab.
Soil Rating System
A soil rating system for subgrade, subbase, or base for use in the design of light traffic
pavements in terms of CBR values is given in Figure 3.65. Typical CBR values for com-
pacted materials are given in Table 3.39.
3.5
Deformation without Rupture
3.5.1
Introduction
Forms of Deformation
Ideal Materials
Elastic deformation: Stress is directly proportional to strain; the material recovers all defor-
mation upon the removal of stress (Figure 3.66a).
 
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