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Earth Pressure Cells
Geotechnical Instrumentation
3500, 4800 Series
Operating Principle
Earth Pressure Cells are constructed from two stainless
steel plates welded together around their periphery and
separated by a narrow gap filled with hydraulic fluid.
External pressures squeeze the two plates together
creating an equal pressure in the internal fluid. A length
of stainless steel tubing connects the fluid filled cavity
to a pressure transducer that converts the fluid pressure
into an electrical signal transmitted by cable to the
readout location.
Advantages & Limitations
The 4800 Series Earth Pressure Cells use vibrating wire
pressure transducers and thus have the advantages of
long term stability, reliable performance with long cables
and insensitivity to moisture intrusion. All models also
include a thermistor for temperature measurements and
a gas discharge tube for lightning protection. Where
dynamic stress changes are to be measured a semi-
conductor type pressure transducer is substituted (see
Model 3500).
Cell performance depends strongly on the surrounding
soil properties. It would be prohibitively expensive to
calibrate a cell in the soil type specific to the application
being contemplated. However, studies have shown that
the most consistent cell performance is achieved using
cells of maximum stiffness with aspect ratios D/t >10
(D is the diameter of the cell, t the thickness). With
Geokon cells, maximum stiffness is achieved by using
hydraulic oil with less than 2 ppm of dissolved gas and
aspect ratios generally greater than 20 to 30. Tests on
Geokon cells in various types of soil have shown that
the cells over-register the soil pressure by less than 5
percent. This is probably no greater than the inherent
variability of the soil pressure distribution in the ground.
Typical of all closed hydraulic systems, earth pressure
cells are sensitive to temperature changes which cause
the internal fluid to expand at a different rate than the
surrounding soil giving rise to spurious fluid pressure
changes. The magnitude of the effect depends to a
greater extent on the elasticity of the surrounding soil,
i.e., on the degree of compaction and confinement, and
is difficult to predict and correct for. The built-in thermis-
tor is helpful in separating these spurious effects from
real earth pressure changes.

Model 4800 Earth Pressure Cell (front), Model 4820 Jackout Pressure Cell (center) and Model 4810 Contact Pressure Cell (rear).
Applications
Earth Pressure Cells provide
a direct means of measuring
total pressures, i.e. the
combination of effective
soil stress and pore water
pressure, in or on Bridge abutments Diaphragm walls Fills and embankments Retaining walls surfaces Sheet piling Slurry walls Tunnel linings
They may also be used
to measure earth bearing
pressures on foundation
slabs and footings and at
the tips of piles.
Earth Pressure Cells Model 4810
Spread Footing
Structure Wall
Lug
Hinge
Second thick
plate
Structure Wall
Lug
Cable
Transducer
Mortar Pad
Model 4800
cells are constructed
from two thin pressure sensitive
plates. They can be positioned in
the fill at different orientations so
that soil pressures can be measured
in two or three directions. Special
armored cables are recommended
in earth dam applications.
The Model 4810 Contact Pressure
Cell is designed to measure soil pres-
sures on structures. The backplate
of the cell which bears against the
external surface of the structure
is thick enough to prevent the cell
from warping. The other plate is thin
and is welded to the backplate in
a manner which creates a flexible
hinge to provide maximum sensitivity
to changing soil pressures.
Lugs on the side provide a means of
mounting the cell to concrete forms
or to steel or concrete surfaces. A
mortar pad beneath the backplate
ensures good contact with the struc-
ture surface. Cells are best installed
flush with the surface to which they
are attached. The fill material next to
the cell should be screened to remove
pieces larger than 10 mm.

Model 4800 Earth Pressure Cell.

Model 4810 installation in a spread footing.

Model 4810 Contact Pressure Cell for attachment to existing concrete surfaces.
Cells installed at the base of slabs
and footings to measure bearing
loads should always be positioned
inside the concrete with the sensitive
face pressed against the compacted
fill. Cells placed in the fill below the
concrete often become decoupled
from the soil pressure due to the
impossibility of adequately compact-
ing the fill around the cell.

Model 4800 Earth Pressure Cells installed
in fill for soil pressure measurement in
three directions.

Model 4815 pressure cell, with two thick
plates, for use in granular materials.
The
Model 4815
is a special cell
that effectively reduces the severity
of point loading when used in granu-
lar materials. The modification uses
two thick plates welded together at
a flexible hinge that helps provide
more uniform pressure distribution.

Side and frontal views of the Model 4810
installed on existing structure.
Model 4800, 4815 Earth Pressure Cells
Model 4810 Contact Pressure Cells
Model 3500 Earth Pressure Cell installed under railroad tracks.
Model 3500 Series Earth Pressure Cells
Hydraulic Hose
Reaction Plate
Reinforcement Cage
Hydraulic Ram
Signal Cables
Concrete
Tremie Pipe
Piezometer
Pressure Cell
Support Plate
Bentonite Slurry
Railroad Tracks
Ballast
Sand Fill
Pressure Cell
Model 4855
Pile Tip Pressure Cell
Rebar
Transducers
Crimper

Jackout Pressure Cell assembly installed in diaphragm wall.
The 3500 Series is similar in design
to the 4800 Series but the vibrating
wire transducer is replaced by a
semi-conductor type transducer (to
enable the measurement of dynamic
pressures) which can have an output
of 2mV/V, 0-5VDC or 4-20mA. Typical
applications are the measurement of
traffic induced stresses on roadway
sub grades, airport runways or under
railroad tracks.
The Jackout Pressure Cell is designed
for installation in diaphragm walls
(slurry waalls) to monitor soil pres-
sures on the walls as excavation
proceeds. This allows the build-up of
excessive pressures to be detected
in time to take remedial measures.
The Jackout Pressure Cell assembly
consists of the cell mounted on a
support plate, a reaction plate and
a hydraulic ram. This assembly is
attached, in its retracted position,
to the reinforcement cage and is
lowered into the slurry trench along
The Model 4855 Pile-Tip Load Cell
is used to measure pile-tip loads in
cast-in-place concrete piles (caissons).
Like the Model 4810, the pile-tip
pressure cell has a thick upper plate.
The cell is manufactured to be close
to the diameter of the pile and the
back plate is supplied with hooks or
sections of rebar to allow the cell
to be connected to the bottom of

Model 4820 shown in hydraulic ram assembly with piezometer and alone (inset).

Model 4855 Pile-Tip Pressure Cell installation
the reinforcement cage. Two vibrat-
ing wire pressure transducers are
connected to the cell to provide some
redundancy in the event that one
transducer is damaged during instal-
lation. An added feature is a remote
crimping mechanism to allow the
cell to be inflated slightly so as to
ensure good contact between the cell
and the surrounding concrete.
with the cage. When the cage is
in position the hydraulic ram is
extended by means of a hand pump
situated at the top of the wall and
connected to the ram by a hydraulic
hose. Pressure is applied forcing the
reaction plate and the cell against
the walls of the trench. This pressure
is maintained while the concrete
is tremied into the trench and until
the concrete cures. The cell may
be supplemented by a piezometer
attached to the support plate to
measure pore water pressures.
Model 4820 Jackout Pressure Cells
Model 4855 Pile-Tip Pressure Cells The World Leader in Vibrating Wire Technology
TM
Geokon maintains an ongoing policy of design review and reserves
the right to amend products and specifications without notice.
Geokon, Incorporated
48 Spencer Street
Lebanon, NH 03766
USA
1 603 448 1562
1 603 448

3216
geokon@geokon.com
www.geokon.com
©2007 Geokon, Incorporated. All Rights Reserved | Doc. Rev. F, 07/07
4800
4810
4815
4820
4855
3500
Transducer Type
Vibrating Wire
Vibrating Wire
Vibrating Wire
Vibrating Wire
Vibrating Wire
Semi-conductor
Output
2000-3000 Hz
2000-3000 Hz
2000-3000 Hz
2000-3000 Hz
2000-3000 Hz
2 mV/V, 0-5 VDC
or 4-20 mA
Standard Ranges¹
70, 170, 350, 700 kPa;
1, 2, 3, 5, 7.5, 20 MPa
350, 700 kPa;
1, 2, 3, 5 MPa
350, 700 kPa
1, 2, 3, 5 MPa
350, 700 kPa;
1, 2, 3, 5 MPa
3, 5, 7, 10.5 MPa
100, 250, 400, 600 kPa;
1, 2.5, 6 MPa
Over Range
150% F.S. (maximum)
150% F.S. (maximum)
150% F.S. (maximum)
150% F.S. (maximum)
150% F.S. (maximum)
150% F.S. (maximum)
Resolution
±0.025% F.S.
±0.025% F.S.
±0.025% F.S.
±0.025% F.S.
±0.025% F.S.
Infinite
Accuracy²
±0.1% F.S.
±0.1% F.S.
±0.