ASTM D 8359 : 2021

1.3.1 This designation is described in the context of obtaining data for the design, construction, or maintenance of structures on or in rock. This method can be conducted in any orientation but is usually conducted in a vertical or horizontal borehole as dictated by the design consideration.

1.3.2 The test has no depth limits other than those imposed by the limitations of the test equipment, drill hole quality, testing personnel, and equipment to drill the holes and position the testing assembly.

1.3.3 Since this is a volumetric test, only the average deformation is obtained around the borehole. If the rock properties, for any reason, including the in situ stress field or fracture density, are significantly anisotropic, then this device cannot detect that difference.

1.3.4 A large expansion of the probe in a test zone can occur due to either an oversized drill hole, weathering, lithology, or discontinuities. As a result, the maximum pressure and expansion of the dilatometer would be limited. For example, for one particular dilatometer to avoid damaging the membrane in a preferred N-size, 75.7 mm (2.98 in.) I.D., borehole, the maximum working pressure of 30,000 kPa (4,350 lbf/in.²) might be possible. In contrast, at 82.5 mm (3.25 in.), the maximum working pressure would drop to only 20,680 kPa (3000 lbf/in.²). Furthermore, regardless of if it an oversized drill hole or a low modulus test interval, the maximum diameter (inflated) of only 85.5 mm (3.37 in.) is allowed.

1.3.5 The radial displacements of the borehole walls during pressurization are calculated from the total volume change of the dilatometer. As such, the test results from a volumetric dilatometer indicates only the averaged value of the modulus of deformation.

1.3.6 The volumetric dilatometer test does not provide the anisotropic properties of the rock mass because it measures the average deformation and not the deformation in specific directions. However, by conducting dilatometer tests in boreholes oriented in different directions or taking impression packer data in any test intervals that had developed a hydraulic type fracture, some aspects of the in situ anisotropic conditions could be obtained.

1.4.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In the system, the pound (lbf) represents a unit of force (weight), while the units for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations are involved.

1.5.1 The procedures used to specify how data are collected/recorded or calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, a purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.