Structural Building Monitoring in the Drilling Phase

By Lucia Faravelli – SIART

The EU GEOFIT project comes with the goal, among others, of linking three main characters: the geothermal technology promoter, the excavation and drilling operator and the structural engineer. Within a geothermal based retrofitting of existing buildings, the first actor designs the geothermal system and dictates the main data to the excavation (drilling) works responsible. The latter one relies on earth moving machines that transfer vibrations to the soil and from here to the target building. The third character has the main role of supervisor that no damage affects the building during the plant installation.

The simplest policy would be to instrument the site and the building and to carry out a structural monitoring in the drilling phase. Currently artificial intelligence tools able to detect the incipient damage are not available. In other words, the deployed devices will only be able to detect and locate damage when this has already seriously progressed. The alternative feasible architecture goes across the knowledge of the excitation source, the identification of the vibration propagation across the soil and the understanding of the so-called building signature, i.e., the building own frequencies. The trick is to avoid amplifications in the pattern from the source to the building of those frequencies to which the building is sensitive. Along this path, the role of structural monitoring will simply be that of checking that the recorded (accelerometric) signals will confirm the numerical models.

Fig. 1 – Drilling activities at the Sant Cugat pilot

Knowledge of the excitation source. Figure 1 above, shows the drilling machine of one of the GEOFIT partners. Figure 2 below is the plot of the vertical component of the acceleration as recorded by an accelerometer on the machine. Finally, Figure 3 gives a plot of the same vertical component of the acceleration as recorded by an accelerometer on the soil nearby the machine. It is worth noticing the differences between the two ranges of intensity.

Propagation across the soil interface. The phenomenon is covered by reliable scientific software adopting sound mechanical models [2]. The role of the monitoring is to confirm that the recorded output is consistent with the model. In other words, there should not be amplification in the frequencies to which the building is sensitive. Building signature. This aspect can easily be solved by carrying out the structural monitoring in a pre-drilling stage [3].

Fig. 2 -Vertical component of the acceleration as recorded on the drilling machine (time in
seconds; intensity in V; conversion 1V = (1/2.5)g). Zoom on the right.
Fig. 3 – Vertical component of the acceleration as recorded on the soil near-by the drilling
machine (time in seconds; intensity in V; conversion 1V = (1/2.5)g). Zoom on the right.


[1] Casciati S.; Chen, Z., A multi-channel wireless connection system for structural health monitoring applications STRUCTURAL CONTROL & HEALTH MONITORING Volume: 18 Issue: 5 Pages: 588-600 Published: AUG 2011

[2] Casciati, F.; Faravelli, L.Dynamic transient analysis of systems with material nonlinearity: a model order reduction approach SMART STRUCTURES AND SYSTEMS Volume: 18 Issue: 1 Pages: 1-16 Published: JUL 2016

[3] Casciati S., Stiffness identification and damage localization via differential evolution algorithms, STRUCTURAL CONTROL & HEALTH MONITORING Volume: 15 Issue: 3 Pages: 436-449 Published: APR 2008

Completion of Civil Works at Perugia

Civil works began on December 3rd, 2020 at the Perugia Pilot. At that time, partner IDSGEORADAR performed a ground-penetrating radar measurements survey. Meanwhile, partner R2M operated UAV flights with and without a thermal camera. And all throughout the drilling phase, partner UNIPG completed the Structural Health Monitoring (SHM).

After one week, the works completed the shallow excavations of up to 2.5 meters deep. This meant the area was ready for the 50 centimeters of the sand bed that increases the conductivity on the ground.

Later, on January 11th, the company in charge of the fieldwork started the installation of the slinky GHEXs that go 2 meters deep. It considers 5 parallel trenches, with 1.35 m of mutual distance, 24 meters of average trench length, and 53 rings for each trench.

After the GHEXs installation, on January 18th, GROENHOLLAND came to the Perugia Pilot to install the fiber optic cable (FOC) monitoring. This technology has a particular approach that allows remote checking of the new system’s performance while matting underground temperature.

To increase the innovative aspects and the scientific relevance, UNIPG installed on the first two trenches, two parallel tubes of a drip plant that allows experimental evaluations and comparisons that consider different boundary conditions and configurations, such as with varying ground hydration content.

Drip plant in the first two trenches.

Finally, civil works were completed on January 28th as soon as all the excavated area was backfilled with an additional 50 cm of sand. Also, the ground excavated material was reused on-site.

Backfilling the area with other 50 cm of sand.

Furthermore, all the heating/cooling system components: heat pumps, boilers, tanks, are available on-site. And today, FAHRENHEIT’s chiller also arrived at Perugia!

Presently, UNIPG is working to complete the whole installation by the end of March and to move forward with the commissioning of the system.