ASTM D4729-19

5.1 Flat jack tests are useful to assess rock mass deformability and stresses in the design stages of projects as well as for issues with existing projects; for example, stresses around an underground opening. The in situ stress values can be used as an important parameter for interpretation and validation of test results and analytical models.

5.2 This test method has been successfully used for other applications such as concrete dams and masonry structures. This test method is similar to the techniques and equipment used in C1196 and C1197. However, this standard is written more for rock and where irregular surfaces may be involved and both in situ stress and deformability are obtained in one test.

1.1 The flat jack test measures the natural or altered in situ stress at a rock surface either for a surface outcrop or an underground excavation surface. The modulus of deformation and the long-term deformational properties (creep) may also be evaluated for the applied stress range, however long-term creep is not covered by this method.

1.2 This method covers square flat jacks that are placed in a rock slot and if required encapsulated in the slot.

1.3 Deformation readings are taken at the surface, but this standard does not exclude deformation readings being taken below the surface, such as using a flat jack which is set up to obtain displacement data internally.

1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.5 Limitation—The flat jack test measures the average stress normal to the surface of the test chamber, underground excavation, or outcrop. In situ stress levels must be determined by theoretical interpretations of these data.

1.6 Assumptions and Factors Influencing the Data: 

1.7 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. Add if appropriate, “Reporting of test results in units other than inch-pounds shall not be regarded as nonconformance with this standard.”

1.8 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.

1.9 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.