Installation Of Model 4820 Jackout Pressure Cell In Slurry Trenches; Figure 14 - Model 4820 Jackout - Geokon 4820 Instruction Manual

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2.2.4 Installation of Model 4820 Jackout Pressure Cell in Slurry Trenches

The Jackout Pressure first needs to be assembled into the Jackout frame. The assembly is
shown in Figure 14. The support plate has a circular hole cut in it and bolt holes to fit the
Jackout Pressure Cell (JOPC), and is connected to one end of a double-acting hydraulic
jack by means of steel struts. The support plate and reaction plate are cambered top and
bottom to prevent them from snagging on the sides of the slurry trench. The reaction plate
is attached to the other side of the double-acting hydraulic jack. The jack is attached
firmly to the rebar cable and arranged so that the plates are free to move outwards. The
hydraulic line and signal cable are tied off to one of the rebars at intervals of one meter (~
three feet).
When the rebar cage has been lowered to its proper depth, the jack is activated, forcing
the two plates out against the trench walls.
Figure 14 - Model 4820 Jackout Pressure Cell Installation
Observation of the pressure indicated by the JOPC (see Section 3 for readout
instructions) will indicate when the cell has made contact with the wall. Pump up the jack
until the JOPC reading indicates a pressure roughly 70 KPa (10 psi) greater than the
slurry pressure at JOPC depth. This ensures that the cell is bearing against the walls of
the trench, and that the concrete grout pressure will not close the jack, which could allow
the reaction plates to move away from the trench walls. Check the JOPC reading from
time to time, because the pressure might bleed away if the walls of the trench are soft and
yielding. Repressurize as needed. Leave the jack pressurized until the grout has set up.