Performance of single and double flat jacks in stone masonry lab tests

Abstract At inspection and diagnostic phases of ancient masonry structures, it is often necessary to evaluate the compressive strength and stiffness of stone masonry of masonry walls. These walls are a heterogenous material, and the number of in-situ test methods is limited, being the flat jack tests the most used ones. Besides other uncertainties in the accuracy of the results obtained with flat jack tests, they are frequently used to estimate the mechanical characteristics of ancient building’s walls. In this paper, results from an experimental campaign are presented and discussed, carried out on a large scale specimen built with limestone masonry and natural hydraulic lime, with the aim of comparing the stress level obtained with the single flat jack test with the real stress. Various recommendations are put forward, regarding the use of this methodology in masonry walls, for validation and determination of the in-situ compressive stress level. Furthermore, test results of double flat jack tests are presented, and a comparison is made between the specimen’s compressive strength, obtained through the double flat jack test and the axial compression test, having obtained relatively close values. All results are compared with the ones of other authors and several conclusions are presented.