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This research has been dedicated to the experimental study of a FrenchPleistocene marl through uniaxial compressive tests on prismatic specimens. Induceddeformations were measured during testing by classical extensometers applied on therock surface and by means of photogrammetrical measurements. The choice of thismaterial was forced by its relative good characteristics in terms of materialhomogeneity when compared with other kinds of marl. The specimen shape was dictatedby the necessity to induce plane deformation during testing to be measured by usingoptical methods. Specific software, implementing a correlation algorithm able to trackhigh deformation fields and model crack propagation was developed and applied todetermine displacement and deformation maps at each photogram on the wholespecimen surface. Photogrammetrical method has been validated by the comparisonwith classical extensometer results. This measurement tool has been specificallydedicated to the identification of the microcrack formation during the performed testsfor a better understanding of weak rock triggering failure phase before crackpropagation start. The interpretation of experimental tests on the light of materialphysical and mechanical features is illustrated in the paper together with all difficultiesencountered in the specimen’s preparation phases due to the material peculiar nature.