Application of a new stress measurement device in underground marble quarrying, a case study

The paper deals with the evaluation of the stress state in an white marble underground quarry (Lasa, Bolzano, Italy), where new exploitation activities are currently in progress. In addition to the geomechanical study, which has shown the influence of the joint pattern on the potential structurally controlled instabilities, particular attention has been given to in situ stress evaluation by means of the stress overcoring method. The measurements were carried out by using the classical CSIR strain cell and a newly developed cell. The results offered by the two devices appear to be in acceptable agreement and suggest a rather high stress level in the natural supporting structures.The newstress measurement device is able to autonomously supply power, perform signal conditioning and continuously acquire data during the overcoring phase. 1 INTRODUCTION The current mechanization and technology level of marble cutting favours a relatively fast enlargement of underground quarry exploitations and makes it necessary to carry out an experimental evaluation of the static condition of the residual rock structures (roofs, walls, pillars) to ensure a safe ore body exploitation. Planning the ground control, which is not a common systematic activity in quarry practice, is driven by the specific geomechanical characteristics of the exploited rock mass at the quarry sites and the exploitation technique (Hoek & Brown 1982, Brady & Brown 1985, Iannacchione & Prosser 1997). Therefore, a monitoring programme, that includes stress state measurement in the residual supporting rock structures, becomes essential for a safe and profitable quarry development. As far as the monitoring devices are concerned (Dunnicliff 1993), the stress variation in supporting rock structures is measured by means of borehole stressmeters which are used to control stress variations, while the stress state, when the most common measurement techniques are utilized, can be measured by the relief techniques, or by stress restoring methods or by hydraulic methods (Amadei & Stephansson 1997).