El Espígol Rock Stability Monitoring Project
The El Espígol Rock Stability Monitoring Project is located in Gerb, Catalonia, Spain. The El Espígol boulder, situated right above the village of Gerb, has a total height of 32 meters and a width of 24 meters. The hill, popularly known as Penya de l’Espígol, has been identified as "potentially unstable" and poses a threat of collapse, which could lead to a disaster. In 2019, deep cracks were noticed on the rock face, causing concern among the residents of Gerb. As a result, the town council initiated an investigation.
Project Details
| Project | Location | Client | Contractor | Duration |
|---|
| El Espígol Rock Stability Monitoring Project | Gerb, Catalonia, Spain | Provincial Council of Lleida | Kuroba Quatre SL | December 2021 – Ongoing (as of Feb 2023) |
Why Monitoring?
When deep cracks in the rock face were noticed, it heightened fears among the residents that the entire rock could collapse at any moment. Kuroba Quatre, a company specializing in natural hazards, proposed an instrumentation and monitoring plan for the boulder. The aim was to collect data for at least one year before deciding on the next steps.
Monitoring Solution
Kuroba Quatre selected Encardio-Rite as the supplier of the instruments to monitor the El Espígol Boulder. Initially, crack meters and inclinometers were installed. However, within two weeks of installation, the sensors detected movements in the rock, prompting an upgrade of the monitoring solution. Load cells and piezometers were added to monitor the remedial actions taken at the site.
Instruments Used
| Instrument | Purpose |
|---|
| Crack Meter | To monitor the width of existing cracks in the rock. |
| Wireless Tilt Meter | To monitor the tilt of the rock. |
| Load Cells | Used to monitor the force on the rock bolts. |
| Piezometers | To monitor sub-surface water pressures. |
In the first stage, two crack meters and two wireless tilt meters were installed. The crack meters were automated using wireless RF data loggers (nodes), and the wireless tilt meters had in-built RF data loggers. These dataloggers transmitted the recorded data via low-power radio frequency to a gateway, which then transmitted the data to a central server via a cellular network. The central server's database management software processed, analyzed, and presented the data in near real-time to all concerned stakeholders.
An acoustic alarm device, activated by an extensometric sensor, was also installed (not within the scope of Encardio-Rite). This device was intended to transmit an immediate alarm to the general population in the event of a movement.
In the second stage, four anchor load cells and four vibrating wire piezometers were installed in addition to the sensors deployed in the first stage. The acoustic alarm device installed in Phase 1 was replaced by a system equipped with a siren that activated the alarm directly from the Data Management System.
Result
The initial plan was to conduct a study over a year, but within two weeks (December 2021), the instruments showed movement, indicating that the rock was cracking. The installed tilt meters recorded a total tilt variation of up to 18 degrees, and the crack meters recorded a displacement of up to 4.89 mm.
In response to this alarming situation, immediate remedial measures were taken. A metal mesh was installed, and rock bolts were placed to restrain the rock's movement. Additional instrumentation, including load cells and piezometers, was installed to monitor both the rock and the stabilization measures. The instrumentation provided real-time data, enabling prompt alerts and timely corrective actions.