This paper aims to introduce a new non-destructive testing technique in use for detecting the occurrence of material instability and a specific data reduction procedure to access damage accumulation. An input-output non-parametric procedure based on ultrasonic pulse propagation, and a non-linear analyser were chosen to portray the unstable behaviour of brittle rock material under static compressive loading. | Vietnam Journal of Mechanics, VAST, Vol. 31, No. 3 &4 (2009), pp. 159 – 165 UNSTABLE BEHAVIOUR OF ROCKS Luong Minh Phong CNRS-LMS, Ecole Polytechnique, Palaiseau France Abstract. This paper aims to introduce a new non-destructive testing technique in use for detecting the occurrence of material instability and a specific data reduction procedure to access damage accumulation. An input-output non-parametric procedure based on ultrasonic pulse propagation, and a non-linear analyser were chosen to portray the unstable behaviour of brittle rock material under static compressive loading. It can be used to monitor non-destructively and continuously the overall alteration or damage process so that damage mechanisms could be quantitatively estimated by a dimensionless parameter the so-called non-linearity ratio. 1. INTRODUCTION In recent years, there has been an increased need for the non-destructive evaluation and testing for civil engineering projects, particularly interesting in inspection and monitoring of geotechnical structures. With the wide application of digital signal processing techniques, the acoustic emission AE and ultrasonic waves are used to evaluate the alteration state or the mechanical performance of a material. The ultrasonic wave properties are measured during propagation through rocks to find out their mechanical properties. Several authors (Lockner et al., 1977; Sobolev et al., 1978) have reported that cracking noise occurred at about 60% to 99% of the ultimate load. It was recognised that these significant changes in rock mechanical behaviour are caused by micro-cracking. Laboratory measurements, indeed sensitive to the presence of existing micro-cracks in rock specimens, detect the failure process, only at the start of dilatancy (unstable cracking) or coalescence appearance. The early beginning of cracking (phase 3 of Bieniawski’s model (1967a): stable cracking) cannot be determined by the velocities (Couvreur et al., 1998). Modification of .
