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