01-32_GENERALS_SUMMER25_PT - Flipbook - Page 17
cannot be used in Type 4 soil, which 昀氀ows
too easily and can collapse the hydraulic
supports over time.
Protect workers with a trench box, a steel
structure designed to withstand the weight
of collapsing soil if trench walls fail. “For
smaller jobs, trench boxes are typically
used due to their availability and convenience,” Smith says. “But it’s important
to note that the box only o昀昀ers protection
when you’re in it.”
Whether you use shoring or trench
boxes, either system must be designed
by a professional engineer based on the
identi昀椀ed soil conditions at your project—and installed per the manufacturer’s
instructions and engineer’s drawings.
How continuous inspections can improve
trench safety
Of course, the goal is to prevent a cave-in
from happening in the 昀椀rst place. Even
with proper sloping and other controls,
it’s important to frequently inspect the
trench walls for signs of weakness. The
longer a trench has been exposed—to
water, evaporation, vibration, and
more—the greater the chance that its soil
conditions could change.
Conduct a thorough inspection at the
start of each workday and at every shift
change. Workers who enter the trench
should also be trained to spot the signs of
soil weakening or failure and should be
continuously looking for them.
“And the construction regulations also
require a worker to be above the trench,
monitoring conditions from there, even if
a trench box is in place,” Smith says.
Cracking is the most obvious sign of trench
weakness, as is water seeping from the
walls (or, conversely, if the trench walls are
drying out). Beyond that, you should also
check any hydraulic supports being used
in the trench for cracks, bends, and other
defects. And monitor the pressure gauge,
too. Under too much force, the hydraulic
struts may leak internally and fail.
If soil weakness is identi昀椀ed, immediately evacuating anyone in the trench is
job number one. Excavation equipment
can be used to strip loose or cracking
material from the wall, before further
sloping is undertaken or additional supports are installed.
But remember that a support system
has to be designed for the soil found in
the trench. “What happens if you thought
you were working in Type 2 soil and your
system was designed for that, but then
conditions change or you hit a pocket of
Type 3 or 4 soil?” Smith asks. “Well, to
ensure worker safety, the law says you
need to redesign the support system for
that new soil type—or at minimum, get
it in writing from your engineer that
the supports are still appropriate for the
conditions.”
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