5 Test procedure
5.1 Assembling the parts
The cover, the membrane and possibly the slotted tube if required shall be selected according to the expected stress-strain parameters of the ground in which the probe is to be used. They shall each fulfil the specifications given in Annex A. Then the probe shall be linked to the control unit through the connecting lines.
The whole system shall be filled with liquid and purged to remove air bubbles.
5.2 Calibration and corrections
Calibration and correction shall be performed according to Annex B. Copies of the calibration results shall be available at the testing location.
5.3 Pressuremeter pocket and probe placing
In pressuremeter testing, it is paramount to achieve a high quality pocket wall. The procedures and requirements in Annex C shall be followed.
The preparation of satisfactory pockets shall be the most important step in obtaining acceptable pressuremeter test results.
Three conditions shall be fulfilled to obtain a satisfactory test pocket:
- the equipment and method used to prepare the test pocket shall cause the least possible disturbance to the soil at the cavity wall (see C.1);
- the diameter of the cutting tool shall meet the specified tolerances (see C.2.2);
- the pressuremeter test shall be performed immediately after the pocket is formed (see Table C.1 and C.1.2 and C.1.3)
NOTE An indication of the quality of the test pocket is given by the shape of the pressuremeter curve and the magnitude of scatter of the test readings (see D.2).
5.4 Preparation for testing
The pressure and volume control unit (CU) and the data logger shall be protected from direct sunlight. The position of the pressuremeter sounding shall be marked on a drawing and identified by its location details. If the sounding is inclined, its slope and direction shall be recorded (see Annex F). As next step, for each sounding:
- the acquisition and recording device, i.e. the data logger, shall be initialized (procedure B);
- the initial reading of each transducer shall be checked and, if appropriate, recorded (procedures A and B).
The identification parameters of the test shall be recorded, either in the memory device or on the data sheet with a carbon copy (see Annex F):
- test operator identification;
- file number;
- sounding number;
- type of probe;
- technique of pocket drilling (see Annex C);
- ground identification and description according to ISO 14688-1 and ISO 14689-1;
- method of probe setting;
- calibrations test references (see Annex B);
- elevation zc of the pressure transducer or value of zc
- zn for this transducer (see Figure D.1);
- elevation zs of the test location or depth (zN – zs) of the probe (see Figure D.1);
- differential pressure setting (see B.4.4).
5.5 Establishing the loading programme
The loading programme of a pressuremeter test shall be the relationship between time and pressure as applied by the probe to the ground (Figure 4).
At each pressure hold the pressure shall be held constant in the central measuring cell and in the guard cells for a time th of 60 s. In procedure A, if a variation in pr during a pressure hold exceeds the greater of 25 kPa or 0,5 % of the current pressure value pr, the final value of pressure shall be recorded.
The initial pressure increment Δp1 to be used shall be decided by the operator after observation of the drilling parameters, examination of the core or the drill cuttings and by instruction. Once the initial readings have been recorded, the operator shall observe the creep parameter ΔV60/30 and the differences ΔV60/60 between successive 60 s volume readings and as a result may change the pressure increment so as to:
- obtain approximately 10 points during the test and
- reach the end of the test (see 5.7.2).
- pt target pressures
- Δp pressure increment
- pr pressure hold during th
- C loading phase
- t time
- ti pressure increment time
- th duration of a pressure hold
- D unloading phase
The time ti for raising the pressure by the next step Δp shall be less than 20 s when the line length is less than 50 m. Appropriate adjustment to ti shall be made for the case of the line length exceeding 50 m (when in coil). Once the test is completed as described in 5.7.2, unloading shall be performed steadily and without stopping.
5.6 Establishing the differential pressure
The pressure of the gas in the guard cells shall be lower than the pressure in the central measuring cell by at least twice the central measuring cell membrane pressure loss pm as defined in B.2.
At the elevation of the control unit (CU), the pressure difference which is necessary to keep the above-mentioned equilibrium is called the differential pressure. It shall be calculated according to B.4.4. This differential pressure shall be set before the start of the test and checked at each pressure hold.
At the jobsite, before carrying out the tests, the operator shall be given a table exhibiting differential pressures as a function of the depth according to the type of probes used.
The expansion process shall include:
- applying a uniform pressure to the pocket wall through the pressuremeter probe according to the loading programme (see 5.5);
- recording the measuring cell volume changes with time as a function of the loading pressure applied to the measuring cell.
5.7.1 Readings and recordings
At each pressure hold the following readings shall be taken:
- in procedure A, the liquid pressure required by the loading programme shall be recorded once and the injected volume in the probe at the following times once target pressure is reached: 15 s, 30 s and 60 s. The liquid and gas pressures, the differential pressure and their variations shall be checked. Excessive variation shall be noted (see also 5.5);
- in procedure B, the applied liquid pressure and the injected volumes in the probe shall be displayed and recorded at least at the following times: 1 s, 15 s, 30 s and 60 s. Readings of gas pressures at the same times may be used for checking.
The origin of the time for each pressure hold shall be taken at the end of the corresponding pressure increment period ti.
5.7.2 End of test
Unless otherwise specified, the test is terminated when sufficient data has been accumulated for the intended purpose, within the full capabilities of the equipment. These will normally be:
- when the pressure pr reaches at least 5 MPa, or
- when the volume of liquid injected into the central measuring cell exceeds 600 cm3 (450 cm3 for a short probe within a slotted tube) or
- when the probe bursts.
NOTE In the event that these conditions are not met, the test can still be fully analysed when three pressure holds beyond pfM are obtained.
5.8 Back-filling of the pockets
Method of back-filling of the pockets resulting from the pressuremeter sounding shall be agreed and carried out in accordance with ISO 22475-1 and national regulations, technical or authority requirements, and shall take into consideration the strata, contamination of the ground and its bearing capacity.
If required, backfilling of the hole in the ground resulting from the pressuremeter sounding shall be completed and documented in the test report.
5.9 Safety requirements
National safety regulations shall be followed; e.g. for:
- personal protection equipment;
- clean air if working in confined spaces;
- ensuring the safety of personnel and equipment;
Drill rigs shall be in accordance with ISO 22475-1 when applicable.