DOI: 10.5281/zenodo.10078265
title: GEOLAB Project FROSPER: FROst heaving soils-Solar Panel foundations interaction in cold European Regions: an experimental study

description: The objective of the proposed project is to investigate the resilience of solar panels foundations in cold climates. The efficiency of solar panels is overall better in cold climates, when the direct sunlight is available, due to the lower temperature-induced dispersion. For this reason, large solar fields tend to be installed in cold regions, such as northern Europe or Canada. A solar field with e.g., 10 MW, requires a great number of solar panels (~6000) whose foundations are generally steel piles driven into the soil down to a depth of 2÷5 m below the ground surface. In the cold regions, the shallow layers of soil are periodically subjected to freezing thus to the frost-heaving phenomena. The latter can increase the risk of uplift failure mechanism of the pile foundation compromising the exercise of the entire solar panel row.
This project aims to investigate the interaction between saturated soils and solar panel foundations under frozen conditions in scaled centrifuge models. The steel piles will be at first driven into the saturated soil sample, then a set of the freezing-thawing cycles will be reproduced in the centrifuge. Possible practical interventions to reduce the soil frost-heaving effects will also be explored, as the use of protective insulating mantel at the ground surface all around the head of the pile.
This project will represent a breakthrough in the understanding of the solar panel foundations behaviour, allowing a deeper insight into possible uplift failure mechanisms. The motivation of the study lies in the reduction of the costs and in the resilience improvement of critical infrastructures for the generation of energy in the EU territories. 
description: Two centrifuge tests reproducing the freezing and thawing cycles of cold climates on several different configurations of solar panel (SP) foundations were carried out in the Turner Beam Centrifuge of the Schofield Center in Cambridge at an increased gravity of 20 g (Test1) and 30 g (Test2), respectively. For each test, 2 cylindrical PMMA boxes with an internal diameter of 190mm and 30mm-thick were filled with a 200mm-high saturated mixture of Huston sand (80%) with Speswhite kaolin (20%) consolidated at 70 kPa. The model piles are made of aluminium with an extruded H-section (6.3 mm x 6.3 mm), and they were driven into the soil mixture at 1g for three different depths in accordance with the prototype pile lengths: short of 2 m, medium of 2.5 m and long of 3 m. One of the box contains two rows of three connected piles enbedded in heterogeneous soil, while the other box contains five single piles: 2 short, 2 medium and 1 long. The effectiveness of insulating squared mantel at the top of the piles was also explored as a frost-heave mitigation intervention. The centrifuge models were instrumented to monitor soil and piles behaviour during the test. Linear Variable Differential Transformers (LVDTs) fixed in the box caps measured the vertical settlements, three strain gauges for each pile measured the local force along the pile shaft, and several PT100 measured the temperature of the air and of the soil at different depths. A Vortex system, which worked with a compressed air line, applied the freezing load at the ground surface, bringing the air temperatures down to values of -15°C. The first centrifuge test ran only freezing for 3h:45min at 20 g, while the second test performed 6h of freezing and 30min of thawing at 30 g.