Standard Test Method for Determining the In Situ Rock Deformation Modulus and Other Associated Rock Properties Using a Flexible Volumetric Dilatometer
|Publication Date:||1 November 2020|
This test method establishes the guidelines, requirements, procedure, and analyses for determining the in situ deformation modulus of a rock mass and other ancillary data using a flexible volumetric dilatometer in an NX drill hole (Fig. 1). Cyclic, creep, and unloading cycles are not covered in detail in this standard but may be added in the future or with a separate test standard, practice, or guide.
NOTE 1-Other rock mass deformability tests are radial jack tests, flat jack tests, flexible plate tests, and borehole jack tests.
This test method applies mainly to a commercially available flexible, volumetric dilatometer for an NX-sized (75.7-mm (2.98-in.)) borehole that is inflated and deflated hydraulically in the borehole. However, the test method could apply to other dilatometers, including pneumatically inflated, or for different borehole sizes as well as covered under the British Standards Institute EN ISO 22476-5.
Purpose, Application, Range of Uses, and Limitations:
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.
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.
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.
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.) boreholes, the maximum working pressure of 30,000 kPa might be possible. In contrast, at 82.5 mm, the maximum working pressure would drop to only 20,680 kPa. Furthermore, regardless of if it an oversized drill hole or a low modulus test interval, the maximum diameter (inflated) of only 85.5 mm is allowed.
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.
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.
Units-The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
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.
All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
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.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.