Geoscience Reference
In-Depth Information
Fig. 17.17. N
q
vs. H
c
/
D for horizontally loaded pipes in dry and moist sand
active zones in front of and behind the pipe, respectively. In contrast, partially saturated
sand ruptures along distinct failure planes, creating a coherent mass of soil that is pushed
forward and lifted in concert with the relative lateral movement of the pipe.
Figure 17.17 shows the maximum dimensionless force, N
q
, vs. dimensionless depth,
H
c
/
D, derived for partially saturated and dry sand tests with the experimental data of
Turner (2004) and Trautmann and O'Rourke (1985). Note that predicted curves for a
friction angle of 30
◦
are not shown in Figure 17.17. Loose, dry sand consolidates during
lateral loading, which, in effect, increases the friction angle and N
q
values, and results in
larger horizontal displacement to attain maximum load. Moist sand placed in the loose
condition typically consists of a bulked, collapsible structure with inconsistent density,
for which a uniform mass friction angle is not appropriate. Lateral loading of pipes in
loose sand will result in collapse of the bulked structure and compaction of the sand,
thereby increasing the dry unit weight and friction angle. With the available evidence
from this and previous studies, a percent increase in N
q
from dry to moist loose sand
cannot be reliably predicted. Further experimental investigation is needed to confirm the
force-displacement behavior of loose moist sand.
