4.4 Test procedure (p. II)

4.4.3 Testing procedure

(1)P The expanding section of the pressuremeter shall be pressurised until the specified diameter as defined in 4.3.1 (2)P is reached. The maximum pressure capacity of the probe shall be consistent with the pressure required to inflate the expanding section in the particular ground conditions as stated in 4.3.2 (2)P. For safety reasons the expansion may be terminated if either the maximum pressure capacity of the probe is reached or if any of the displacement transducers has reached its full working range or the maximum safe expanded volume is reached.

(2) The pressuremeter may be unloaded to produce an unload-reload cycle. The rates of unloading and reloading should be specified.

(3) Prior to unloading there can be a period during which the pressure or displacement is held constant.

(4) The reduction in stress during any unload-reload cycle should be specified.

(5) The strain at the start of any additional unload-reload cycles may be specified.

(6)P The output from the transducers shall be recorded at a minimum frequency of 10 s. intervals throughout the test if automatic recording is used, or 30 s. if manual readings are taken or shall be specified.

(7) For MPM tests recordings or readings are conventionally taken at 15 s, 30 s and 60 s after pressure application is completed.

4.4.3.1 Stress controlled tests - Ménard method

(1)P With the Ménard stress controlled method tests shall be carried out at a constant rate of pressure increase. The increments shall be adjusted to ensure that there are at least seven increases in pressure throughout the loading stage, however ten increases are preferred.

(2)P Each pressure increment shall be held constant for 1 min.

4.4.3.2 Other stress controlled tests

(1)P Incremental stress controlled tests shall be carried out at a constant rate of pressure increase.

(2) One unload-reload cycle, if required, can be included in the loading sequence when either the cavity has increased in diameter by between 1 % and 3 %, or when the pressure has reached 10 MPa, whichever occurs first.

(3)P The increments shall be no greater than 5 % of the maximum capacity of the probe and shall be adjusted to ensure that there are at least fifteen increases in pressure throughout the loading stage (excluding any unload-reload cycles).

(4) The size of the pressure increments may be adjusted during the early stage of the test to ensure that a sufficient number of readings can be taken to accurately define when the membrane comes in contact with the side of the hole and shall be no greater than 0,2 MPa.

(5)P Each pressure increment shall be held constant for 1 min.

4.4.3.3 Strain controlled tests

(1)P Strain controlled tests undertaken with a PBP shall be carried out using constant increments of volumetric or cavity strain. The increments shall be adjusted to ensure that there are at least twenty increases in volume throughout the loading stage.

(2)P Each increment shall be maintained for 1 min.

(3)P Strain controlled tests undertaken with an SBP shall be carried out at a constant rate of stress increase during the early stage of the test. Once expansion starts, a constant rate of strain of 1 % per minute shall be used.

(4)P Strain controlled tests undertaken with an FDP shall be carried out at a constant rate of stress increase during the early stage of the test. Once expansion starts, a constant rate of strain shall be used.

(5)P A sufficient number of readings shall be taken to define accurately the pressure at which expansion starts.

(6) An unload-reload cycle, if required in a PBP test, should be carried out when either the hole has increased in diameter by between 1 % and 3 % or when the pressure has reached 10 MPa, whichever occurs first.

(7) An unload-reload cycle, if required in an SBP test, should be carried out when the hole has increased in diameter by between 1 % and 3 %.

(8) An unload-reload cycle, if required in an FDP test, may be carried out once constant pressure conditions are approximately achieved.