10.4 Test procedure

10.4.1 Calibration and checks

(1)P All measuring devices shall provide reliable and accurate measurements.

(2)P Prior to performing each test series, and periodically during a testing program or after major repair, the complete dilatometer equipment shall be thoroughly checked, with the probe and the hydraulic and pressurizing systems filled with the pressurizing fluid, thoroughly bled to remove any entrapped air and pressurized to check for leaks.

(3)P The probe shall be inflated in air, without confinement, and measurements taken to obtain an unconfined pressure-dilation relationship from which the stiffness of the flexible membrane shall be determined.

(4)P When using probes fitted with displacement transducers that measure the dilation of the membrane relative to the inner cove, instead of relative to the borehole wall the membrane compression shall be determined prior to testing.

(5)P When using equipment that allows measurements of fluid pressure and of volume of displaced fluid at ground surface only, the hydraulic system stiffness shall be determined prior to testing.

(6)P The hydraulic system stiffness shall be determined from knowledge of the stiffness of the calibration cylinder and of the overall stiffness of the hydraulic system plus calibration cylinder.

(7)P The overall stiffness of the hydraulic system plus calibration cylinder shall be determined from a pressure - dilation graph obtained with the probe inserted in the calibration cylinder by increasing the fluid pressure in increments and measuring the corresponding volume of displaced fluid. The pressure shall be increased through the range of pressures specified for the required testing program to obtain at least five measurements of pressure and corresponding volume of displaced fluid.

10.4.2 Performing the test

(1)P After the hole is completed the diameter and clearance shall be checked and recorded prior to inserting the probe.

(2) Borehole clearance should be checked using a cylindrical gauge of the same size as the probe. The wall of the borehole should be checked for fissures, voids and rock fragments, that might damage the flexible membrane or trap the probe.

(3)P The position of the probe at the required test depth shall be measured with an accuracy of ± 50 mm and recorded.

(4) When a continuous profile of deformability is required the vertical depth increment between successive test elevations should vary between 1 m and 5 m.

(5)P After the probe has been positioned at the required test depth, it shall be inflated to apply at first the seating pressure that shall be the minimum pressure throughout the test.

(6)P With the probe seated the pressure shall be increased in at least five approximately equal increments to the maximum possible value not exceeding the safe operation pressure of the testing equipment.

(7)P Measurements of the applied pressure and of the volume of displaced fluid or of the borehole dilation shall be taken and recorded at each pressure increment. Each increment shall be held for a period sufficiently long to determine whether the rock behaviour is time dependent.

(8) Time dependent behaviour and creep rates should be evaluated by maintaining the volume of fluid inside the probe constant while the drop in pressure with time is recorded or by maintaining the fluid pressure constant while the increase of borehole dilation with time is recorded.

(9)P The maximum pressure shall be maintained constant for at least 10 min. and measurements of volume of displaced fluid or of borehole dilation shall be taken and recorded throughout this length of time.

(10) Measurements of the applied pressure and of the volume of displaced fluid or of the borehole dilation should also be taken and recorded during unloading.