Giorgia Dalla Santa

Embankments and other compacted earth structures are widely used in civil engineering, and their mechanical behaviour depends on the properties of compacted soils, which are often affected by unsaturated conditions and matric suction. This study presents an empirical methodology aimed at the preliminary estimation of the peak friction angle of compacted unsaturated soils from cone penetration test (CPT) data, intended to support engineering assessments when laboratory testing and site investigation are limited. The approach was developed using CPT measurements collected at three levee test sites in northeastern Italy (Grizzaga, Panaro, and Tagliamento Rivers), combined with laboratory shear test results on undisturbed samples and supplemented by selected data from the literature. Three empirical equations were proposed and compared using different normalization schemes of cone tip resistance with respect to in situ stress conditions, while considering the influence of matric suction. For the soils examined in this study, the estimated peak friction angles were generally consistent with laboratory results, suggesting that the proposed relationships may provide a reasonable first approximation under similar soil conditions. The proposed procedure is intended as a preliminary engineering tool to complement, rather than replace, detailed laboratory testing in the geotechnical characterization of levees, embankments, and other compacted earth structures.

The effective operation and monitoring of levees constitute pivotal factors in managing and safeguarding lowland territories during flood events and in regular flow conditions. Given their longitudinal structure and spatial soils heterogeneity, the monitoring of levee functionality poses complex challenges. This study investigates the application of a hybrid monitoring system combining traditional sensors and distributed temperature sensing (DTS) to assess seepage in a river levee in the northeast of Italy. The system, installed along three verticals at the levee toe, included pressure transducers and a DTS cable deployed using cone penetration test (CPT) equipment. The DTS system was deployed at the downstream toe of the levee on the landward side to detect temperature variations indicative of anomalous seepage within the levee body, assuming that water filtering through the levee exhibits a distinct temperature signature. To enable this installation method, a special disposable drill tip was developed and here discussed. Monitoring data collected over three years suggest seepage occurred primarily through shallow, permeable layers. This outcome guided the definition of the interventions aimed at mitigating local water seepage, providing insights both pre- and post-construction. Additionally, several finite element method (FEM) analyses of the instrumented levee section were carried out through a parametric study to assess the hydraulic and thermal conditions influencing thermal signal propagation within the levee, rather than to directly reproduce site-specific measurements, for a reliable use of DTS data to detect seepage. The study identified soil permeability as the dominant factor, with thermal properties and hydraulic gradient becoming significant only for low-permeability soils. The monitoring data guided an optimized intervention strategy, limiting sheet pile installation depth and reducing costs. Post-intervention monitoring validated the effectiveness of the intervention. This case study demonstrates the value of integrating advanced sensing technologies with traditional geotechnical practices and numerical modeling to enhance embankment safety assessment and guide targeted, cost-effective interventions.

The European Union has set an ambitious goal of achieving net-zero emissions by 2050, and 90% reduction by 2040, through its Green Deal policy. A promising solution to this challenge lies in the adoption of Fifth-Generation District Heating Networks (5GDHNs) that operate at low temperatures, collecting and distributing heat from diverse sources (energy geostructures, asphalt pavement solar thermal collectors, industrial waste heat and waste heat from buildings’ cooling plants). The system’s design allows for heat storage underground, primarily during summer months, with distribution occurring via pipelines during winter. As part of the REHEAT project, a study has been conducted focusing on a simulation model developed using TRNSYS software. This model incorporates solar thermal collectors installed beneath the parking area asphalt pavements as a thermal energy source, coupled with a borehole thermal energy storage system. The setup is designed to meet the heating and cooling demands of a multiplex cinema situated in Northern Italy. The study presents the optimization of the system, reporting the monthly and annual data on energy balances and system efficiency. The findings demonstrate significant energy savings when compared to traditional heating and cooling systems (50.6% non-renewable primary energy reduction) and even greater CO₂ emission reduction (63.2%). Also, the economic analysis reveals positive results both from the point of view of operating costs and taking into account investment costs, highlighting the potential of 5GDHN as a sustainable solution for urban energy needs for a real case as the main novelty of this study.

Closed-loop geothermal systems offer a low-risk alternative for exploiting high geothermal gradients in volcanic environments; however, the influence of borehole geometry on long-term performance under shallow, high-temperature conditions remains poorly constrained. This study presents a systematic numerical comparison of five closed-loop borehole heat exchanger (CBHE) configurations vertical, deviated, horizontal, U-loop, and single-lateral under geological conditions representative of Vulcano Island (Italy). A fully coupled 1D wellbore 3D formation thermo-hydraulic model was developed to simulate conductive heat transfer and fluid circulation over 25 years of continuous operation. The modelling framework isolates geometric effects by assuming conduction-dominated heat transfer in the surrounding formation, providing a baseline assessment of configuration performance. Results demonstrate that borehole geometry exerts a primary control on long-term thermal behaviour, exceeding the influence of operational parameters such as injection temperature and flow rate. Lateral configurations significantly enhance performance by increasing effective heat-exchange length, fluid residence time, and enlarging the effective heat-exchange volume within high-temperature formations. After 25 years, horizontal, U-loop, and single-lateral systems stabilise at production temperatures of approximately 147–165 °C, compared to 96–101 °C for vertical and deviated configurations. Inner-pipe insulation reduces thermal short-circuiting, particularly during early operation, while outer-pipe insulation provides secondary benefits. Although simplified boundary conditions neglect convective heat transfer and represent a conservative scenario for volcanic systems, the relative performance ranking among configurations remains robust. These findings highlight trajectory design and lateral development as key optimisation strategies for closed-loop geothermal deployment in shallow, high-enthalpy volcanic environments.

Closed-loop geothermal systems offer a low-risk alternative for exploiting high geothermal gradients in volcanic environments; however, the influence of borehole geometry on long-term performance under shallow, high-temperature conditions remains poorly constrained. This study presents a systematic numerical comparison of five closed-loop borehole heat exchanger (CBHE) configurations vertical, deviated, horizontal, U-loop, and single-lateral under geological conditions representative of Vulcano Island (Italy). A fully coupled 1D wellbore 3D formation thermo-hydraulic model was developed to simulate conductive heat transfer and fluid circulation over 25 years of continuous operation. The modelling framework isolates geometric effects by assuming conduction-dominated heat transfer in the surrounding formation, providing a baseline assessment of configuration performance. Results demonstrate that borehole geometry exerts a primary control on long-term thermal behaviour, exceeding the influence of operational parameters such as injection temperature and flow rate. Lateral configurations significantly enhance performance by increasing effective heat-exchange length, fluid residence time, and enlarging the effective heat-exchange volume within high-temperature formations. After 25 years, horizontal, U-loop, and single-lateral systems stabilise at production temperatures of approximately 147–165 °C, compared to 96–101 °C for vertical and deviated configurations. Inner-pipe insulation reduces thermal short-circuiting, particularly during early operation, while outer-pipe insulation provides secondary benefits. Although simplified boundary conditions neglect convective heat transfer and represent a conservative scenario for volcanic systems, the relative performance ranking among configurations remains robust. These findings highlight trajectory design and lateral development as key optimisation strategies for closed-loop geothermal deployment in shallow, high-enthalpy volcanic environments.