4.3 Equipment

4.3.1 Apparatus

(1)P The expanding section of a pressuremeter, defined in 4.2, shall have a length to diameter ratio greater than 5.

(2)P The diameter of the flexible membrane shall be capable of expansion without bursting by:

  • 50 % if the Ménard method is required;
  • 50 % if an FDP is required;
  • 25 % if a PBP is required;
  • 15 % if an SBP is required in soils;
  • 10 % if an SBP is required in weak rocks.

(3)P If a volume displacement type probe is used, volume changes shall be measured either in the control unit, at the surface, or in the probe.

(4)P If a radial displacement type probe is used, displacements shall be measured directly on the membrane circumference, at three or more equidistant points in the plane perpendicular to the axis through the centre of the probe.

(5)P The thrust machine and push rods used to jack an FDP into the ground shall comply with the specification for cone penetration tests.

4.3.2 Measuring equipment

(1)P Volume measuring gauges shall be capable of measuring changes in volume equal to 100 % or 50 % of the initial volume of the expanding section of the probe depending on the test method specified (100 % for the Ménard method).

(2)P The applied pressure shall be measured either in the control unit at the surface or in the probe and the gauge or transducer shall have a sensitivity compatible with the pressure range required for the ground being tested.

(3)P The working range of a pressure transducer or gauge shall be suitable for the ground to be tested.

(4)P The resolution of all electrical measuring devices and any associated data acquisition systems shall be within 0,1 % of their full working range. The resolution of all other measuring devices shall be within 1 % of their full working range.

4.4 Test procedure (p. I)

4.4.1 Calibrations

(1)P Calibrations for all probes shall be reliable, repeatable, accurate and traceable to standards.

(2)P Results of all calibrations shall be available on site for inspection.

(3)P The following calibrations shall be required:

  • volume displacement type probes:
    • pressure transducers or gauges;
    • volume displacement gauges;
    • system expansion;
    • membrane stiffness;
    • membrane compression (if testing rock);
  • radial displacement type probes:
    • pressure transducers;
    • displacement transducers;
    • membrane stiffness;
    • membrane compression (if testing rock).

(4)P Transducers and gauges shall be calibrated prior to the start and following the completion of the testing programme. For MPM testing this only applies if no calibration has been performed within the last 6 months.

(5)P Calibration of membrane stiffness shall be carried out prior to the start of testing on site and after the completion of every borehole. A new membrane shall be calibrated before use.

(6)P The displacement and pressure transducers shall be re calibrated following any repair of the transducers readout/control unit and connecting cables.

4.4.2 Installation

(1)P The probe shall be installed in such a manner that the disturbance to the surrounding ground is kept to a minimum for the type of probe.

(2)P Boring to form a test hole below the base of a borehole for the insertion of an MPM or PBP shall be carried out using equipment, techniques and a flushing medium consistent with achieving minimum disturbance. For any particular test hole sampling requirements shall be specified.

(3)P The boring techniques and flushing medium used with a SBP shall be consistent with achieving minimum disturbance to the ground surrounding the probe.

(4)P The initial volume of a deflated volume displacement type probe shall be determined at the surface before it is lowered into the borehole.

(5) The orientation of the probe may be recorded prior to the start of insertion into the borehole and before it is removed, particularly when radial displacement probes are used.

4.4.2.1 Ménard and other prebored pressuremeters

(1)P The diameter of the test hole shall be kept close to the diameter of the deflated probe, but shall not be less than the diameter of the deflated probe.

(2)P If a test hole is to be used for one test only, then the probe shall be inserted into the test hole within 60 min after completion of drilling the test hole, provided the depth to the test hole does not exceed 30 m. For holes below that, more time may be used.

(3)P If the borehole is of a larger diameter than the test hole then the distance between the top of the expanding section of a probe and the base of the borehole shall be at least half the length of the expanding section.

(4)P For a long test hole in which a number of tests will be carried out, all boring and testing shall be completed within one working shift.

4.4.2.2 Self-boring pressuremeter

(1)P The SBP shall be bored continuously from the ground surface or from the base of a borehole. It shall be bored a sufficient distance beyond a previous test position or beyond the base of a borehole into ground that is unaffected by either the previous test or the drilling of the borehole.

(2)P The minimum distance between test locations shall be equal to twice the distance between the centre of the expanding section and the base of the probe. If a length greater than that distance is required, then the length to be self-bored shall be specified.

(3)P During self-boring of a SBP the setting, type and rotational speed of the cutter, type and characteristics of drilling fluid, the drilling fluid pressure, rate of advance and ram pressure shall all be adjusted to ensure minimum disturbance without causing undue risk of damage to the equipment.

(4)P In free draining soils an expansion test shall be started as soon as practically possible following the completion of self-drilling. In all remaining soils and weak rocks there shall be a minimum of 30 minutes and a maximum of one hour between completion of self-boring and the start of the expansion test.

4.4.2.3 Full displacement pressuremeters

(1)P When a FDP incorporates an electrical cone, it shall be jacked into the soil between test levels at (20 ± 5) mm/s either from the base of a borehole or from the surface.

(2)P An expansion test shall be started as soon as practically possible following the completion of jacking.

Eurocode 7 Geotechnical design — Part 3: Design assisted by fieldtesting