The Pencel Pressuremeter
Sunil Sundaram
Foundation Design
Spring 2004
About the Pressuremeter Instrument used to run in-situ soil loading tests by
expansion of cylindrical cavity 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
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
Figure 5.2: PPMT Control Unit (After Roctest 1986a)
Cylinder/piston asssembly
To probeFill/Bleed
Pressure Gauge
Fiberglass box
Volume counter
Handle cover
00000
2500
0
kPa
Test
Test
Closed
Fill Bleed
Valves
Tubing
64
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
Pressure correction Volume loss correction
Probe Insertion Probe is connected to EW steel drill rods Hydraulic pressure used to insert rod
Pressuremeter – Working contd… Test Execution
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…
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
Current technique is very tedious and error-prone
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 Measures displacement of a piston causing
volume change Connected in parallel with piston using mounting
brackets and linkage rod Pressure Transducer
Measures pressure corresponding to volume change
Connected in series with existing pressure gauge
Instrumentation contd…
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
Recording of data process is faster Less manpower required to conduct tests Less human error