Use of a miniaturized data-logger for determining the state of stress induced in abandoned pillars

The measurement of the natural and/or induced stress state in rock masses excavations is generally carried out thanks to techniques able of providing results both in the two-dimensional (2D) and in the three-dimensional (3D) environment, coded in the "Suggested Method"of the ISRM. The stress relief method is one of the most consolidated measurement methods, based on the differences in strain intensity evaluated in selected directions before and after making a continuous notch around the sensors involved in the measurement. With a special miniaturized data-logger applied to the sensors used for the evaluation of the rock stress in a 2D (doorstopper) or 3D (HI cell, CSIRO) environment, the execution of the measurement on site can be considerably simplified, and the complete strain-time diagram acquired due to over-coring can be obtained. The paper presents an example of measurement of the state of stress induced in some abandoned pillars in an underground quarry.