We live near Carrara, the town where the world’s most popular and most sold marble is extracted, Carrara marble.
Marble quarries are as impressive and scenic as they are dangerous.
Indeed, they are often the place of fatal accidents.
This is why the safety of marble quarry workers is a priority for the Tuscany Region.
What is MONFRON?
MONFRON is the acronym of “Monitoraggio Fronte di cava” which translates as “Front of Quarry Monitoring system”.
This is a large project, which was presented to the Tuscany Region in 2017. The project was funded in January 2018 and sees Lunitek as the lead company, together with Santucci Graniti Srl, the quarry owner, and ApiAn the rock climbing organisation.
The project idea is to prevent the sudden and unexpected rockslide falling on quarry workers. Prevention cannot be carried out using traditional instruments for geophysicist (accelerometers, velocimeters, GNSS or laser scanners) because, by the time these types of systems trigger an alert, in most cases, it is already too late, and the rockslide cannot be stopped.
Lunitek presented a proposal for monitoring by employing an Acoustic Emission (AE) technique over a period of 18 months.
How Acoustic Emission technique works?
Acoustic Emission (AE) is the phenomenon of radiating acoustic waves in solids that occurs when a material undergoes irreversible changes in its internal structure. This is due to the rapid release of localized stress energy. Acoustic Emissions can be detected in a frequency range from few KHz up to 100Mhz, but most of the released energy is from 1KHz to 1 MHz.
Thanks to AE technique it is possible to localize the source of the emitting event.
Lunitek has been working in this field in close collaboration with the Polytechnic University of Turin since 2008.
Professors from Structural Department (Carpinteri, Lacidogna, Bertetto, Niccolini) worked with us to transfer their know-how and to design a cutting-edge technology product.
All these efforts have led to the AEmission an 8-channel fast-sampling datalogger with a parametric processing of the acquired data.
AEmission is an eight channel datalogger for acoustic emission waves.
It can sample data at 1.25MS/s@18bit or at 10MS/s@16bit.
Piezo-ceramic sensors can be connected directly to the instrument without any external conditioner.
An internal high-performance FPGA performs real-time analysis of the data stream coming from the ADCs and extracts the parametric data.
Why Acoustic Emission is the right tecnique?
Acoustic Emission (AE) is the only technology that can spot a potential cracking fractures inside a solid.
The idea is to trigger an alert when abnormal conditions are detected on the data processing.
Since we are talking of an experimental investigation, the site is also monitored with other techniques:
- ATLAS with an external FBA accelerometer on the quarry front 1.
- TRITON FBA accelerometer outside the monitored site.
- A meteorological station.
- A thermocouples array installed on the quarry front 2.
All this information can help to discern false events from real cracking events.
The system has been deployed as shown in the below pictures
Statistic analysis of B-value and βt parameter
On the below picture some of the monitoring fundamental parameters. In particular it is possible to notice a reduction of the fundamental parameters related to the damage evolution (b-value). It is also possible to notice the appearance of some points of acoustic emission locate on the monitoring front n.2
Result and conclusions
Based on the data highlighted by the localization technique and in correlation with the values assumed by the critical parameter of the b-value, it is possible to consider the areas corresponding to sensors 1-7 and 2-4 as critical areas. In these areas, in the central phase of monitoring, the parameters that mark the evolution of the damage highlighted sub-periods with a localized increase of the damage.
The total amount of the founding received from the Tuscany Region was 282.000€