Choosing the Right Shoring for Your Project,"By Gabrielle Shirdon and Ed Oakley, Published in Trenchless Technology Magazine
Even
trenchless projects require shoring from time to time and when
necessary, these can take the form of steel sheet pile and bracing or
slide rail. Shoring is used on jobsites where pipe jacking, boring and
directional drilling are necessary and the job is in a confined work
area where adjacent structures such as railway lines, roadways and
utility crossings are present.
These
trenchless shoring techniques are designed for safety, ease of
installation and to reduce labor costs. It is the contractor's job to
evaluate these solutions and choose which works best for the project
and make sure it is engineered properly.
Hydraulic Waler Framing System
Traditional installation methods
of sheet pile and bracing require impact hammers with cranes and leads
and extensive welding of the walers to create a support frame. Now
there is another product on the market that reduces the size, reduces
installation time and saves you more money. The new system is called
the Hydraulic Waler Framing System.
Mabey
Bridge & Shore, a national company specializing in shoring systems,
is one of a limited number of companies to offer this innovative
system. The Hydraulic Waler Framing System consists of heavy-duty
walers that can provide a clear span up to 52ft. Additional lengths are
possible by supplying hydraulic or mechanical struts. Walers are
modular with a moment connection to provide a variety of lengths. The
walers are also provided with hydraulic ends that adjust up to 3.1ft.
Installation time onsite is reduced by the use of a male/female pinned
end, therefore no cutting or welding of steel is required.
No waler
seats need to be welded to the sheet pile due to the use of hanging
chains. An excavator mounted vibratory hammer is suitable for driving
sheets; this reduces crew size and the cost of additional equipment
such as cranes with leads, impact hammers, or crane mounted vibratory
hammers with separate power packs. This can cut costs from the
traditional methods by thousands of dollars.
Most
applications require sheet pile with toe-in and walers in the top few
feet of the excavation. Alternative application can be supplied if
toe-in for the sheet pile is not an acceptable option. When rock is
encountered at the bottom of the excavation, a no-toe design can be
used with multiple levels of bracing. The pinned corner connections and
hydraulic walers facilitate the installation of walers lower levels.
Slide Rail System
In
contrast, the slide rail system appears more like a panel shield or
box. The slide rail system consists of double walled steel panels,
vertical rails, and steel cross braces of various designs depending on
the soil loads and system configurations. It is installed by pushing
the panels and vertical rails into the ground by an excavator. The
interior earth is excavated as the slide rail is pushed into the ground.
This is
a good solution because a dig and push method is used which is
vibration-free and provides solid support for the surrounding earth and
adjacent structures; it is also easy to put together and the variety of
panel sizes ensures flexibility in its configurations. Another benefit
to the slide rail system is that it can be installed and removed
completely from aboveground.
In
general, the type of shoring solution used for a construction project
depends on the cost, available equipment, soil type, the nature of the
project and contractor experience and preference. What is certain is
that the scheme needs to be engineered by a registered professional
engineer and abide by OSHA standards. Contractors are careful to select
the proper equipment because the wrong equipment could cost them a lot
of time and money and decreased productivity. Not to mention possible
loss of lives.