Environmental Engineering Reference
In-Depth Information
(a)
Gage
Gage
Surface
Detectors
Detectors
Surface
Photon paths
Min = 50mm (2 in.)
Source
Photon paths
Source
Direct Transmission
Backscatter Mode
(b)
FIGURE 3.3
(a) Sand cone density device being used to measure
in situ
density of a compacted subgrade test section for an
airfield pavement. (b) Nuclear moisture density meter used to measure
in situ
density.
Measurements of D
R
Laboratory testing:
See ASTM D4254-00 and Burmister (1948). Maximum density is deter-
mined by compacting tests as described in the above section, or by vibrator methods
wherein the dry material is placed in a small mold in layers and densified with a hand-held
vibrating tool. Minimum density is found by pouring dry sand very lightly with a funnel
into a mold.
D
R
measurements are limited to material with less than about 35% nonplastic
soil passing the No. 200 sieve because fine-grained soils falsely affect the loose density. A
major problem is that the determination of the natural density of sands cannot be sampled
undisturbed. The shear-pin piston (see
Section 2.4.2)
has been used to obtain values for
γ
N
,
or borehole logging with the gamma probe is used to obtain values (see
Section 2.3.6).
Field testing:
The SPT and Cone Penetrometer Test (CPT) methods are used to obtain esti-
mates of
D
R
.
Correlations:
Relations such as those given in
Figure 3.10
for various gradations may be
used for estimating values for
γ
D
and
γ
L
.
