Effect of Uncertainty in Design Decisions for Driven Piles in Soil with High Boulder Content

Driven piles can be severely damaged during driving into soil with high boulder content and can potentially lose their structural integrity, resulting in premature pile refusal. This can cause large additional project cost and delays, including an urgency to change the design in progress. Geotechnical uncertainties related to the spatial variability of soil's boulder content aggravate the complexity of the problem, making it difficult to assess the probability of premature pile refusal due to boulders and to identify the optimal pile design and driving strategy. Existing tools for drivability assessment are mainly deterministic and excessively simplistic, relying on the technical expertise of the personnel involved in the design and execution of the project rather than adopting a systematic treatment of the uncertainties at the specific geological location. A transparent methodology to support the decision-making in pile design is necessary for a cost-effective driving and optimal design solutions. This paper discusses how pile design can be understood from a risk perspective, with specific focus on the assessment of pile drivability. It is found that a new probabilistic approach that provides a correlation between the results from site investigations with the quantities of boulder in the soil layer by inverse analysis can create a solid basis for decision-making in pile design.