Experimental validation for the application of the ﬂat jack test in cob walls Alejandro Jiménez Rios a,⇑ , Dermot O’Dwyer a a Department of Civil, Structural and Environmental Engineering Trinity College Dublin, College Green, D02 Dublin, Ireland highlights  First time ﬂat jack tests are performed in cob walls.  Cob’s compressive strength, Young’s modulus and Poisson’s ratio were obtained.  The average compressive stress seems to be over-estimated by a factor of two.  A value of K e ¼ 0:51 is suggested to correct the average compressive values.  Cob wallette’s failure patterns are reported. graphical abstract article info Article history: Received 28 August 2019 Received in revised form 5 April 2020 Accepted 9 April 2020 Keywords: Cob Minor Destructive Tests (MDT) Single ﬂat jack Double ﬂat jack Mechanical properties Dimensionless geometrical efﬁciency constant abstract The ﬂat jack test is one of the most applied investigation techniques in the ﬁeld of cultural heritage con- servation. The purpose of the experimental campaign presented in this paper was to assess the feasibility of the technique to measure the average compressive levels of stress in existing cob walls and determine their mechanical properties. It was observed that the single ﬂat jack test tended to overestimate the aver- age value of stress by a factor of two. Therefore, it is advised to apply a value of K e ¼ 0:51 to correct the average compressive stress values obtained with the use of this technique. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction The ﬂat jack test is one of the most applied investigation tech- niques in the area of cultural heritage conservation, where the information obtained with this method is used, to assist with the inspection, diagnosis and intervention’s design of existing struc- tures [1]. Other advantages of the ﬂat jack test are that it can also be applied for control purposes while interventions are being carried out [2] and the fact that damages caused by its application can be easily repaired, thus preserving most of the authenticity value of the historic building under study. Originally developed to be implemented in the ﬁeld of rock mechanics [3], the ﬂat jack test has been adopted and used during the last four decades to determine in situ the levels of stress and the mechanical properties of different types of masonry (ashlar, brick, stone) and earthen (adobe and rammed earth) walls. Table 1 shows a list of the research performed on the application of this test to the study of different earthen structures. Despite its popularity and widely spread use by conservation engineers, there are no results available https://doi.org/10.1016/j.conbuildmat.2020.119148 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jimnezra@tcd.ie (A. Jiménez Rios). Construction and Building Materials 254 (2020) 119148 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat