E1001A-171107
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6.2 CALIBRATION FOR VOLUME CORRECTION
This calibration must be done each time after assembling a membrane and saturating the
system. IT IS SUGGESTED TO REPEAT THIS CALIBRATION EVERY DAY OF USE
OF THE PRESSUREMETER TO ENSURE THAT 1) THERE IS NO LEAK, 2) THAT AIR
DID NOT INFILTRATE THE PRESSUREMETER, AND 3) THAT SYSTEM EXPANSION
HAS NOT CHANGED SIGNIFICANTLY. This procedure allows determining the system
expansion in order to calculate the net cavity volume change. The system expansion
comes from tubing expansion, membrane squeezing and from the compression of the
small quantity of air in the fluid. Typically it ranges from 0.006 to 0.016 cm
3
/ kPa,
depending on the T
ecalan’s length.
When a special test is to be performed (cyclic test, creep consolidation test, stress level
influence test…) with a special loading sequence, then a special calibration performed by
following a similar loading sequence is suggested.
1. Connect the Tecalan tubing to port No. 1.
2. Place valve No. 6 on "TEST".
3. Place the probe inside a rigid steel pipe: NW or AW drill casing or equivalent for the 70
and 44 mm diameter probes respectively.
4. Rotating the crank handle clockwise until reaching 500 kPa. Start chronometer. Maintain
pressure around 500 kPa by slightly rotating crank handle if necessary. Stop cranking at
least 5 seconds prior to recording readings. Record volume and pressure after 60
seconds.
5. Install the large crank handle.
6. Increase pressure by another 500-kPa step and take readings after 60 seconds as
described above. Repeat this procedure to 6,000 kPa.
7. When tests in very hard material are to be done
– where it is expected to exceed 6,000
kPa during the test - follow the same calibration procedure but using 1,000 kPa
pressure steps up to 10,000 kPa
8. Return the piston to its lowermost position to decrease the pressure and volume close
to 0.
Warning: Deflation of the probe must be done slowly
– see warning at section 5.1
7
TEST EXECUTION
7.1 MAKING OF THE BOREHOLE
The preparation of a quality borehole is essential for obtaining a satisfactory test. The
two most important things are 1) to make a borehole with a proper diameter (between
1.03 and 1.15 x diameter of the probe); 2) to cause the least disturbance possible to the
borehole wall. Various methods can be used depending on the type of soil and available
equipment. Rotary drilling with axial injection of prepared mud is the most versatile
method and is recommended for most cases. Methods using injection of fluids are
especially suited for the TEXAM since this pressuremeter requires fluid in deep
boreholes (deeper than 10 m) for deflating the probe.
7.2 INITIAL READINGS
1.
De-airing the unit.
Just before the test, disconnect the Tecalan tubing from the
control box, put the saturation hose in a bottle filled with water or anti-freeze, and de-