ABSTRACT Correlations between cone penetration test (CPT), tip resistance, q c' , and pile shaft friction, t f , have been shown to be reliable for evaluating axial pile capacity. The correlation between t f and q c is not direct, and pile shaft friction is influenced by many more factors than those which affect cone tip resistance, namely differences between open- and closed-ended piles/penetrometers; the reduction in local friction with continued pile penetration (friction fatigue); changes in radial stress during loading; and interface friction angle. This paper presents results from analytical studies, model pile test results and field pile load tests in siliceous, micaceous and calcareous sands to assess the influence of sand grain mineralogy on input parameters for CPT q c based shaft friction calculations. While the data for calcareous and micaceous sands are limited, observations based on laboratory and field studies are consistent. The paper concludes that while input parameters may differ, the same framework is valid for evaluating shaft friction in siliceous, calcareous and micaceous sands from CPT data. Calcareous and micaceous sands appear to have higher rates of degradation of local friction than siliceous sands, but this degradation tends to be bounded by a minimum shaft friction value. Input parameters to a general expression for shaft resistance based on the UWA-05 design method are proposed for each sand type. INTRODUCTION A sound design method leads to a safe and cost effective engineering solution with consistent levels of reliability for the anticipated range of situations encountered over the design lifetime. For piled foundations, previous successful experience and static or dynamic load testing plays a significant role in developing such design methods. However, experience alone cannot guarantee reliability, and there is a clear need to develop design frameworks that reflect the current best understanding of the underlying factors controlling pile capacity. Such understanding is critical for offshore piles currently being considered in new regions and in soil conditions that have not been previously encountered 1 . Of the 600 failures of civil engineering systems reviewed by Bea 2 , a majority of failures during operation and maintenance were attributed to flawed engineering design. While these structures and foundations may have been designed to accepted standards, failures occurred due to limitations and imperfections embedded in the standards 2 . This paper is concerned with the design of axially loaded driven piles in sand. The comments of Bea 2 are particularly relevant to this topic, as the underlying behaviour governing the installation and subsequent axial capacity of piles driven in sand is poorly understood. This uncertainty is compounded by a lack of relevant data to support design formulations. Virtually no measurements of the axial capacity of a driven pile with the dimensions relevant to new offshore developments exist. The databases used to calibrate current design methods predominantly comprise short, small diameter piles. Every design of a full-scale offshore pile is therefore reliant on the design method providing a correct extrapolation from the database pile geometry to the field conditions. It is therefore essential that the design method formulation captures the underlying mechanisms as closely as possible.

Abstract To enable optimal design of shallow foundations, anchors and pipelines, it is common practice to test seabed samples at the anticipated consolidation stresses. The direct simple shear (DSS) apparatus has proved to be a favoured means by which the response of a calcareous sediments can be characterised Previously unpublished DSS data for a fine-grained calcareous sediment, presented herein, has helped reinforce the theory that some calcareous sediments exhibit cyclic resilience at low consolidation stress levels that are disproportionately high when compared to the cyclic resilience shown when tested under elevated consolidation stress levels. When analysing DSS test results, a direct proportionality between cyclic strength and consolidation stress has traditionally been adopted. Data presented in this paper helps confirm and extend the relevance of previous work that suggested that the cyclic resilience of certain (in that case, coarse-grained) sediments more closely reflects their behaviour under monotonic loading, with the strength being related to the consolidation stress by a power function, i.e. square-root. Up to now, some difficulty has been experienced obtaining reliable and repeatable test results at low consolidation stress levels that conform with the theoretical expectations. It is suggested in this paper that the reason may be associated with previously unnoticed preferential slip at the platen interfaces in the DSS apparatus Simple modifications to the apparatus have been implemented successfully to minimise this effect and allow more reliable definition of the cyclic resilience of these sediments at low consolidation stress levels It is considered that the information contained with the paper may prove especially useful to designers of shallow foundations in calcareous sediments. INTRODUCTION The direct simple shear (DSS) apparatus (eg. Airey & Wood, 1987) has become a favoured method to establish the undrained cyclic strength of uncemented seabed sediments, which often forms the primary basis for the design of offshore shallow foundations, anchors and pipelines, including seismic liquefaction studies. In their state of the art presentation of the laboratory testing of calcareous soils, Carter et al. (2000) reproduce convenient design charts for calcareous sand and silts that represented a reasonable average of DSS data from many offshore projects. Charts like these suggest that cyclic strength is directly proportional to the consolidation stress Airey and Fahey (1991) used this assumption when summarising the cyclic strength of silty sand from the North West Shelf in Australia Finnie et al. (1999) presented data from DSS tests performed on calcareous sand from an offshore project in the Philippines and modified the assumption of direct proportionality to consolidation stress, indicating that cyclic resilience tended to reflect the monotonic strength. This concept was originally suggested by Andersen et al (1994) for non-calcareous soils. The term cyclic resilience (rather than strength) was used to define the resistance a sediment has to accumulating strain under particular cyclic load levels, given that the sediments tested were always able to sustain the demanded load, without collapsing This paper presents some data from DSS and triaxial tests performed on calcareous silt, sand and clay sized soils recovered from the seabed in the in the Timor Sea, supported by data from the Malampaya development in the Philippines