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1.1 This test method is used to determine the in situ modulus of deformation of rock mass by subjecting a test chamber in rock of a circular cross-section to uniformly distributed radial loading; the consequent rock radial displacements are measured at various locations, from which the deformation modulus may be calculated. The radial anisotropic deformability of the rock is taken at enough locations that it can also be determined from the differences between the extensometer readings taken at various locations along and around the test chamber as well with depth from each loading sequence. Information on time-dependent deformation may be obtained as well by holding the loads constant for selected time intervals.

1.2 This test method is based upon the procedures developed by the US Bureau of Reclamation, featuring long extensometers that provide a bottom anchor far enough away from the test zone to be used as a zero reference point (Fig. 1)(1).2 An alternative procedure, the New Austrian method, is also available and is based on a reference bar going down the middle to support posts outside the deflection zone due to the testing loads and shown in Fig. 2 (2). Other than a different method of taking deformation readings, the two field tests are the same. Additional information on radial jacking and data analysis is presented in References (3-8).

FIG. 1 General Diagram and Scheme of a Radial Jacking Test Setup used by the US Bureau of Reclamation (1, 9)

FIG. 2 Longitudinal, Cross-section, and Close-up View of the Radial Jacking Test Setup (2)

Circled numbers: 1. Measuring profile. 2. Distance equal to the length of active loading. 3. Control extensometer. 4. Pressure gauge. 5. Reference beam. 6. Hydraulic pump. 7. Flat jack. 8. Wood spacer for reaction frame curvature compensation. 9. Concrete. 10. Excavation diameter. 11. Measuring diameter. 12. Extensometer drillholes. 13. Dial gauge extensometer. 14. Steel rod. 15. Expansion wedges. 16. Excavation radius. 17. Measuring radius. 18. Inscribed circle for flat jacks. 19. Rockbolt or extensometer anchor. 20. Reaction frame ring.

The example shown here is the Austrian method and, while outdated, shows most of the essential components of the more common setups.

1.3 Application of the test results is beyond the scope of this test method, but may be an integral part of some testing programs. (See Note 2.)

1.4 Testing of the in situ rock deformation behavior is limited by the maximum stress range of the reaction frame and the flat jacks.

1.5 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are rationalized mathematical conversions to SI units that are provided for information only and are not considered standard. Reporting of test results in units other than inch-pound shall not be regarded as nonconformance with this test method.

1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.

1.7 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.

1.8 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.

5.1 Data on the response of a rock mass to in situ loading provides essential information for many purposes in the science of rock mechanics, in the construction of dams, tunnels, bridges, high-rise structures, and other facilities that exert pressure on the foundation material or surrounding rock mass.

5.2 This test method is similar to a pressuremeter or dilatometer test in rock boreholes. The most significant difference is it engages a much larger volume of the rock mass. By testing a larger rock volume, the influence of discontinuities and other geologic factors on rock mass response to loading is more accurately determined. (Fig. 3)

FIG. 3 Modulus of Rock Mass

Radial jacking test engages a larger volume of the rock mass than with other test method options, such as laboratory (E_lab) and borehole tests other than some geophysical borehole and cross-hole tests.

5.3 This test method should be used when values are required which represent the rock mass properties more accurately than can be obtained through less expensive uniaxial jacking tests, laboratory, or other test methods or procedures. Also, it could be valuable for obtaining such data before or after computer modeling to verify and fine-tune any computer model output.

5.4 Examples of when this test method would be useful is to design pressurized unlined or lined tunnels and shafts.