| Trench digging
is one of the oldest types of construction work documented in history.
Prior to World War II, trenches were dug by hand. As workers dug trenches
deeper, the sides of the trench had to be shored, or supported, to keep
the walls of the trench from collapsing. Following the war, innovations
were made in cable backhoes, and trench digging disappeared as an
established profession. By the 1950's, hydraulically-actuated backhoes
were developed, making it possible to rapidly dig very deep trenches. As a
result of backhoe innovations, and because there were no workers inside
the trenches during digging, trench walls were no longer shored.
A ll trenches have what is known as a stand-up
time. The stand-up time is the time that elapses from the time the trench
is dug until the trench walls start collapsing. Stand-up time is dependent
on many factors, including soil type, water content, trench depth, weather
conditions, and whether or not the soil has been previously disturbed.
Stand-up times can be as short as zero seconds or as long as several
months, and are difficult to predict. Before trenches are dug, someone can
take soil samples as a means of estimating stand-up time; however, soil
conditions can be dramatically disparate only a few feet from where the
soil sample was taken.
A fter a trench is dug, workers go down into the
trench, performing whatever work is necessary, such as laying pipe or
telephone lines, welding pipe, or installing valves.
I f the walls of the trench are not supported,
there is the possibility that the walls will collapse and trap the workers
in the trench. Historically, there have been between 100 and 300 people
killed in the United States every year due to trench collapses.
(Information for the previous story was obtained from http://ethics.tamu.edu/ethics/trench/trench.htm
and is a part of Texas A&M studies.)
W all shields have played an incredibly vital role
in protecting workers who risk their lives on a daily basis. These wall
shields have advanced dramatically from simple wooden structures to
enormous steel shields and massive columnar like cross members to ensure
their strength. The wall shield design is unique to the operation it
performs. The wall shield illustrated on the right is typical of a
trench shield where workers would work in an area the size of the trench
shield. In others the cross members would actually be higher (high
clearance shield). In these high clearance shields workers can easily pass
underneath the cross members and move along a much longer trench in
safety. Yet another type of wall shield resembles a box with 4 enclosed
sides. Many types of shields can be linked together and/or stacked to
allow a larger work area or deeper trench. |
CAD Drawing of the Reuhl Products
Wall Shield/Trench Box |
