15 AUGUST 2005
Plastic soils with high natural moisture are difficult to process for proper
moisture for compaction
Stratified soils may require extensive mixing of borrow.
Embankments on Stable Foundation. The side slopes of fills not
subjected to seepage forces ordinarily vary between 1 on 1-1/2 and 1 on 3. The
geometry of the slope and berms are governed by requirements for erosion control and
maintenance. See Engineering Manual for Slope Stability Studies for procedures to
calculate stability of embankments.
Embankments on Weak Foundations. Weak foundation soils may
require partial or complete removal, flattening of embankment slopes, or densification.
Analyze cross-section stability by methods of UFC 3-220-10N.
Embankment Settlement. Settlement of an embankment is caused by
foundation consolidation, consolidation of the embankment material itself, and
secondary compression in the embankment after its completion.
See UFC 3-220-10N for procedures to decrease foundation settlement or
Significant excess pore pressures can develop during construction of fills
exceeding about 80 ft in height or for lower fills of plastic materials placed
wet of optimum moisture. Dissipation of these excess pore pressures
after construction results in settlement. For earth dams and other high fills
where settlement is critical, construction pore pressures should be
monitored by the methods of UFC 3-220-10N.
Even for well-compacted embankments, secondary compression and
shear strain can cause slight settlements after completion. Normally this
is only of significance in high embankments, and can amount to between
0.1 and 0.2 percent of fill height in three to four years or between 0.3 and
0.6 percent in 15 to 20 years. The larger values are for fine-grained