Laboratoire de geo-energie - Chaire Gaznat en geo-energie

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The safety verification of in-plane loaded masonry panels requires the evaluation of at least three different collapse conditions connected with overturning, shear sliding, and shear - compression failure at the panels' toe. In reinforced panels, the resisting models should even take into consideration the presence of localized or distributed reinforcement. In general, the masonry is considered a Mohr-Coulomb type material not resisting tension and plastic in compression, while reinforcement is a brittle elastic material resisting tensile forces only [1]. The ultimate limit state is however linked with a given subset of compressed material inside the panel area. The compressed sections are therefore varying inside the panel as a function of the applied load. The collapse occurs in shear or overturning when one peculiar compressed section reduces to its minimum [2]. By equating the capacity in shear and overturning it is possible to derive an explicit statement of the minimum length of the compressed section which will be activated by a simultaneous failure in shear and overturning. A simple inequality is detecting the real failure mode and this allows directly computing the failure load resultant. The procedure is very fast and can deal even with localized or distributed reinforcement layers such as fiber strips or mesh reinforced mortars. Some examples of panels discussed in the literature show the effectiveness of the proposed verification procedure.

INT CENTER NUMERICAL METHODS ENGINEERING2021

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2022

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Improving the Accuracy of Fracture Toughness Measurement in Burst Experiments

Guanyi Lu, Yixuan Zhang

Experimental studies suggest that the fracture toughness of rocks increases with the confining pressure. Among many methods to quantify this dependency, a so-called burst experiment (Abou-Sayed, 1978) may be the most widely applied in practice. Its thick wall cylinder geometry leads to a stress state resembling the subsurface condition of a pressurized wellbore with bi-wing fractures. The fracture toughness of a sample, under a given confinement pressure, can be recovered from the critical pressure upon which the bi-wing cracks propagate. Traditionally, this critical pressure is thought to correspond to a sudden drop in injection pressure. However, as the standard configuration was deliberately designed to obtain stable fracture growth at the onset, propagation can take place well before this drop in pressure, and one may overestimate the fracture toughness from measured pressures. Here, we study crack stability in the burst experiment and propose modifications to the experimental design which promotes unstable fracture growth and makes the critical pressure less ambiguous to interpret. We found that experiments with the original, stable design can lead to inconsistent measurement of fracture toughness under confining pressure, while results from unstable configurations are more consistent. Our claim on the stability was also supported by the recorded acoustic emissions from both stable and unstable experiments.

SPRINGER WIEN2022

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