ASTM D4729-19 PDF Download

The ASTM D4729-19 standard describes a procedure for determining the in situ stress and deformation properties of rock surfaces. The test method involves the use of flat jacks placed in a rock slot or encapsulated in a slot, which are then subjected to stress. Deformation readings are taken at the surface, although it does not exclude the possibility of taking readings internally using a flat jack.

The standard highlights the importance of obtaining in situ stress values for interpreting and validating test results and analytical models, especially in design stages and existing projects. It explains that the flat jack method has been successfully applied in various applications, such as concrete dams and masonry structures, but this standard specifically focuses on rock and the potential involvement of irregular surfaces.

The standard also acknowledges that the precision of the test method depends on the competence of the personnel performing it, as well as the suitability of the equipment and facilities used. It emphasizes that compliance with recognized testing practices is crucial but does not guarantee reliable testing. Factors such as material variation, the purpose of obtaining data, and special considerations should be taken into account for each user's specific objectives.

Additionally, the standard mentions limitations and assumptions associated with the flat jack test. It states that the test measures the average stress normal to the surface and that in situ stress levels must be determined through theoretical interpretations. It assumes an elastic and reversible stress relief process, isotropic and homogeneous rock mass, 100% efficiency of the flat jack, and correct alignment with the principal stresses on the surface being measured.