First steps into the calibration chamber pile tests with glauconitic sands

Abstract

The Global Wind Energy Council (GWEC) forecasts an accelerated increase in wind installations as a result of the aggressive climate change and green energy objectives set by the majority of countries. As a consequence, new regions worldwide that were previously thought to be unsuitable for the construction of offshore wind farms due to the soil characteristics are planned to be explored. This is the case of glauconite sands, which include glauconite pellets that are very susceptible to crushing. The crushing transforms the coarse-grained sand into a fine-grained soil, changing the geotechnical characteristics of the soil. This poses particular geotechnical challenges, since the soil-structure interaction between the pile being driven and the sand changes, the side friction increases with depth and the prediction of blow counts in drivability analyses is underpredicted. In addition to this, the glauconitic sand influences the response in cone penetration tests (CPTs), characterised by high cone tip resistance (qc) and sleeve frictions (fs), leading to high friction ratios (Rf) and resulting in misleading soil classifications. IQIP, as a company specialised in installation and foundation projects internationally that provides innovative and high-quality equipment and solutions for construction projects related to Offshore Wind industry, is interested in better understanding the mechanical behaviour of glauconite sand during pile installation due to the risks posed by this sand, e.g. premature pile installation refusal. In order to understand this soil that poses geotechnical challenges, laboratory test programs should be designed in order to capture the soil behaviour and physical modelling is a cost effective and valuable tool. This research aims to obtain detailed information on the soil response of glauconitic sand in saturated conditions during pile installation with a new sample preparation method for glauconitic sand containing fines. It will investigate the feasibility of cone penetration testing, cyclic loading, pile driving, as well as the analysis of the shear band and grain crushing around the instrumentation penetrated in the sample in a calibration chamber (CC). Based on the results from the three performed tests it could be concluded that the preparation method led to a good procedure to prepare repeatable and homogeneous samples under fully saturated conditions, as well to a representative response to pile penetration. With this, it is possible to perform further research on the sand fraction of glauconitic sands using the same sample preparation method and testing equipment.