Annex A

(normative)

Geometrical features of pressuremeter probes

A.1 Geometrical specifications for probes

Table A.1 shall be read in conjunction with 4.1 and Figures 3 and A.1.

NOTE It may occur that the inner part of the slotted tube described above is used as a 44 mm outside diameter probe with flexible cover in smaller diameter borehole. Conversely, 76 mm diameter probes can be used. They consist either of a 74 mm flexible cover probe or of a 58 mm flexible cover probe used as inner part of a slotted tube probe.

A.2 Selecting pressuremeter probe and components

The pressuremeter probe pressure loss, including the slotted tube when applicable, shall be as small as possible when compared with the expected value of the limit pressure at test depth.

Key

• 1 probe axis
• 2 gas supply pipe
• 3 liquid supply pipe
• 4 membrane and cover fixing rings
• 5 rubber cover
• 6 central measuring cell rubber membrane
• 7 drain valve
• 8 slotted tube

The choice of probe major components shall be guided by the following conditions:

a) for the central cell membrane p_m ≤ 80 kPa

b) for the whole probe

when p_LM ≤ 900 kPa, then p_el ≤ p_l/4 + 25 kPa

when p_LM ≥ 900 kPa, then p_el ≤ min {[p_l/18 + 200 kPa]; 350 kPa }

Annex B

(normative)

Calibration and corrections

B.1 Measuring devices

All control and measuring devices shall be periodically checked and calibrated against reference standards (ENV 13005:1999) to show that they provide reliable and accurate measurements. The calibration interval shall be such that the resolution required can be verified.

NOTE 1 Verification of the required resolution can be based on the record of previous calibrations.

The uncertainties of measurements summarized in E.2 shall be considered.

If one part of the system is repaired or exchanged the calibration shall be verified.

A copy of the latest calibration test report shall be available at the job site.

In addition to the calibration of the measuring devices, corrections shall be applied to the field readings for the pressure loss and the volume loss of the whole equipment. If the stiffness of the central measuring cell membrane is not given by the supplier, then it must be independently measured as given in B.2.

NOTE 2 Pressure loss is due to the added stiffness of the central measuring cell membrane, the flexible cover and the slotted tube (if any). It varies with the probe inflated volume.

NOTE 3 Volume loss is due to the expansion of the pressure line, the pressure measuring device and the compression of any gas contained in the liquid injected into the central measuring cell. It varies with the probe pressure.

B.2 Pressure loss of central measuring cell membrane alone

The pressure loss value p_m which is a constant value for each batch of central measuring cell membranes shall be obtained from the membrane supplier. If this information is not available, it shall be determined by using an inflation test on each membrane as described in B.2.1 and B.2.2.

The membrane pressure loss value shall be known before testing so as to set the correct pressure difference between the central measuring cell and the guard cells.

B.2.1 Preparation of pressuremeter probe for central cell membrane pressure loss test

The probe shall be fitted with the central measuring cell membrane only, connected by a short connecting line (less than 2 m) and held vertically. The central measuring cell and the line shall be purged to remove air bubbles. Then the membrane shall be inflated at least three times by injecting a volume of liquid equal to 700 cm³ (or 550 cm³ for a short probe used within a slotted tube).

For this operation, the pressurizing and read-out unit shall be fitted with a pressure measuring device accurate to better than 10 kPa.

The device measuring the injected volume shall be zeroed by bringing the centre of the measuring cell to the level of the pressure measuring device.

B.2.2 Measurement of central cell membrane pressure loss

The membrane shall be inflated in pressure increments Δp equal to 10 kPa. Each pressure level shall be held constant for 60 s. The volume of liquid V₆₀ measured at 60 s shall be used to plot the curve:

V₆₀ = f(p)

The membrane pressure loss p_m shall be given by the pressure for which the volume of liquid injected in the cell is equal to 700 cm³ (550 cm³ for the short probe in a slotted tube).

B.3 Checking measuring devices at site

Readings of the analogue and digital indicating instruments of the control unit (CU) shall be compared with any other available measuring device (e.g. against display of the data logger, additional pressure gauges, etc.) at least at the beginning of each new contract. Any difference shall be investigated.

Further, the control unit shall be checked for correct operation of pressure and volume measuring devices as specified in a written procedure, for instance by comparing the readings obtained on the various pressure transducers and in the case of procedure B between the volumeter and the data logger display.

The equipment shall be corrected, replaced or repaired when the difference between readings is larger than the following values:

• a) for pressure readings either
  • 5 % of the mean value of the two readings, or
  • 1 % of the full scale measurement, whichever is the larger;
• b) for volumes: 3 cm³.