Single flat jack tests

The single flat jack test is a technique used to obtain an esteem of the local state of stress within a masonry wall under compression. The method relies upon the variation of the local stress state caused by a flat cut made in a direction normal to the wall surface.
The stress release that occurs causes a partial closure of the cut, which is detected through the measurements of the relative distance between pairs of points placed in a symmetrical position with respect to the cut. A flat jack made using thin welded steel sheets, connected to the hydraulic circuit of a pump, is then inserted inside the cut.
The internal pressure in the jack is then gradually increased: the test is considered completed when the initial measurements are restored and the corresponding pressure read on the jack corresponds to the local tension in the masonry, considering the multiplicative constants kA and kM.
Reference standards: ASTM C 1196 – 14a; RILEM TC177 MDT.D.4.