TM 5-818-1 / AFM 88-3, Chap. 7
Table 11-1. Excavation Protection-Continued
Soil Type
Identification
Problems and Mechanism
Preventative Measures
(1) Geologic maps and
Open cavities and cav-
(1) Avoid infiltration; col-
local experience
erns; soft infilling
lect surface runoff and
(2) Borings and soundings
in joints, cavities.
convey it to a point
to determine cavity
Dewatering can cause
where its infiltration
locations
cavity collapse or
will not affect
settlements of in-
excavation
filling materials
(2) Eliminate leaks from util-
ity or industrial piping
and provide for inspec-
tion to avoid infiltra-
tion continuing after
correction
(3) Avoid pumping which
causes downward seepage
or recharging
Collapsing soils
(1) See figure 3-16,
(1) When infiltrated
(1) Drainage and collection
Yd vs WL plot
with water, sudden
system to avoid water
(primarily
(2) Yd < 85 PCF
decrease in bulk
infiltration
lbess and vol-
canic ash)
(3) Large open "structure"
volume; may or may
(2) Preload excavation area,
with temporary source
not require load-
and pond with water to
of strength
ing in conjunction
cause collapse prior to
(4) Liquid limit < 45%
with seepage
excavation
plasticity index 0-25%
(2) Water action re-
(5) Natural water content
duces temporary
well below 100%
source of
saturation
strength, usually
(6) Optimum water content
capillary tension
for collapse between
or root structure
13-39%(3)
Low erosion
(Continued)
(Sheet 2 of 3)
11-7
Previous Page
