The Pencel Pressuremeter
Sunil Sundaram
Foundation Design
Spring 2004
About the Pressuremeter
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Instrument used to run in-situ soil loading tests by
expansion of cylindrical cavity
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Helps in the calculation of modulus of elasticity of the soil
Leads to the calculation of lateral pressure acting on the
piles.
Consists of two main parts
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Read out unit that rests on the ground surface
 This unit has both a pressure and volume reading
 Corresponding pressure can be obtained with the
change in volume in the cylindrical cavity
Probe inserted into the borehole
Fiberglass box
Fill/Bleed
To probe
Tubing
Test
Fill
Bleed
0
2500
Valves
kPa
Closed
Pressure Gauge
Test
Cylinder/piston asssembly
0000 0
Volume counter
Handle cover
Figure 5.2: PPMT Control Unit (After Roctest 1986a)
Pressuremeter - Working
Filling and saturation of the control unit


Control unit should be saturated to ensure no air
is trapped in the cylinder or filling lines
Calibrations
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Pressure correction
Volume loss correction
Probe Insertion

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Probe is connected to EW steel drill rods
Hydraulic pressure used to insert rod
Pressuremeter – Working contd…
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Test Execution
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Valve turned to “Test” position once desired depth
has been reached
Constant volume increments of 5 cm3
Pressure measured after rest period
Rest period could vary with soil type
On completion of test, deflate probe
Remove probe or advance probe to lower level
Pressuremeter – Working contd…

Interpretation

Draw the raw data curve and corrected
pressuremeter curve (Pressure vs. Volume)
Pressuremeter – Working contd…
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Each point on the raw curve corresponds to a
point on the corrected curve
V corrected = V read – V calibration
P corrected = P read – P calibration + P hydro
Dismantling and Mounting of a Pencel Probe
Automation - Purpose
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
Current technique is very tedious and errorprone
Automation could:


Reduce human errors and to make the recording
process fast
Allow evaluation of rest time required for the
stabilization of soil pressure (depending on soil)
Instrumentation

Linear Potentiometer

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Measures displacement of a piston causing
volume change
Connected in parallel with piston using mounting
brackets and linkage rod
Pressure Transducer

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Measures pressure corresponding to volume
change
Connected in series with existing pressure gauge
Instrumentation contd…
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Both assemblies will be small enough to
mount within the existing case
Rechargeable power supply used to keep
system portable
Setup connected to the serial port of a
computer
Analog pressure and volume readings will be
converted to digital readings and recorded
with help of Analog – Digital converter
Conclusion
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Recording of data process is faster
Less manpower required to conduct tests
Less human error