Review of CPT Direct Design Methods for Driven Cast-In-Situ Pile Capacity Using Instrumented Pile Load Tests to Failure

Pile design methods using CPT (cone penetration testing) data have been developed over many decades and are widely used in industry. CPT-based site investigations are economic, efficient and suitable for brownfield sites. They also provide a means for characterising the ground within spatially restricted environments in applications such as assessing potential reuse of existing deep foundations. Despite this, driven cast-in-situ (DCIS) piles is a category of pile construction receiving limited attention, perhaps given that CPT-based research is often focussed on preformed driven piles. DCIS is typically classified as a large displacement pile albeit sharing aspects of its construction with replacement pile types. Additionally, there are few published case histories of load tests, let alone instrumented full-scale tests to failure, on DCIS piles from which to understand whether they behave more akin to a full displacement pile. This paper presents a critical review of twelve CPT direct design methods to determine DCIS total pile capacities, using results from six load tests taken to failure on sacrificial piles (ranging from 6.6 m to 9.5 m in length) at Avonmouth, England. The 380 mm diameter DCIS test piles were driven through normally consolidated very soft estuarine clays into an underlying granular founding stratum with varying depths of embedment. This case study presents a unique opportunity to evaluate commonly used CPT design approaches (both simplified and advanced) as applicable to closed-end piles, and actively contribute to the publicly available DCIS database to assist with future design and research. The applicability and limitations of using CPT data for pile base capacity determination is discussed with respect to closed-end displacement piles.