excavation components

Innovations such as finger guards and faster hydraulic pumps, quality control,
customer service, and presentation of tabulated data all help to
differentiate the manufacturers. However, because some parts are
inter changeable and because of the advent of replacement parts also
coming from different sources, it can be hard to identify the original
manufacturer. Since manufacturers hesitate to give out their design
and manufacturing information for competitors and new entrants
into the market to use, it is hard to find a set of engineering calculations
for trench jacks. OSHA only requires that the tabulated data
have a registered engineer’s stamp, and they do not review the engineering
calculations. Engineers who review shoring submittals are
asked to take the tabulated data on faith that the manufacturer’s
engineer knows what she or he is doing. The following engineering
calculations are intended to provide a more detailed understanding
of the structural aspects of trench jacks.

The design concept around trench jack engineering (Fig. 9.12) is
to first look at the safe working load, or bursting strength, of the
hydraulic cylinder and then check to be sure that all the components
will support the safe working load. The piston is axially loaded and
can fail in buckling. The cylinder barrel, in addition to confining the
fluid, has a bending moment applied to it due to the bending movement
of the piston arm. The oversleeve receives a bending load from
the buckled piston. Neither the barrel nor the oversleeve receives an
axial load. There is a 3/8-in pin at the dead block end holding the oversleeve
and the dead end piston block in place, and there are 3/8-in pins
holding the dead block and hydraulic block to the rail. The pins act
strictly to hold the jack together for handling and installation and are
FIGURE 9.12 Hydraulic trench jack cylinder.


From the excavations engineering handbook.