UFC 3-220-01N
15 AUGUST 2005
TABLE 8-1.2
Factors Controlling Excavation Stability
Construction
Objectives
Comments
Activity
Investigate soil compressibility and
Dewatering
To prevent boiling,
effect of dewatering on settlement of nearby structures;
softening, or heave
consider recharging or slurry wall cutoff. Examine for
in excavation
presence of lower aquifer and need to dewater. Install
bottom, reduce
piezometer if needed. Consider effects of dewatering in
lateral pressures on
cavity-laden limestone. Dewater in advance of excavation.
sheeting, reduce
seepage pressures
on face of open cut,
and eliminate
piping of fines
through sheeting.
Excavation and
Pipe trenching,
Analyze safe slopes (see UFC 3-220-10N) or bracing
Grading
basement
requirement (see Chapter 3), effects of stress reduction on
excavation, site
over-consolidated, soft or swelling soils and shales. Consider
grading.
horizontal and vertical movements in adjacent areas due to
excavation and effect on nearby structures. Keep equipment
and stockpiles a safe distance from top of excavation.
Excavation Wall
To support vertical
See Chapter 6 for wall design. Reduce earth movements and
Construction
excavation walls, to
bracing stresses, where necessary, by installing lagging on
stabilize trenching
front flange of soldier pile. Consider effect of vibrations due to
in limited space.
driving sheet piles or soldier piles. Consider dewatering
requirements as well as wall stability in calculating sheeting
depth. Movement monitoring may be warranted.
Dewatering
To prevent boiling,
Investigate soil compressibility and effect of dewatering on
softening, or heave
settlement of nearby structures; consider recharging or slurry
in excavation
wall cutoff. Examine for presence of lower aquifer and need
bottom, reduce
to dewater. Install piezometer if needed. Consider effects of
lateral pressures on
dewatering in cavity-laden limestone. Dewater in advance of
sheeting, reduce
excavation.
seepage pressures
on face of open cut,
and eliminate
piping of fines
through sheeting.
8-4
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