Axial capacity of offshore piles in micaceous soils

The effect of mica particles on the mechanical behaviour of granular materials, and in turn the capacity and stiffness of foundation elements installed in these soils, has been observed by numerous authors. The presence of mica particles has been reported to cause reduction of shear-wave velocity, constrained modulus as well as the peak friction angle of sand formations. These effects are mainly due to bridging whereby platy particles may form bridges over round particles and cause an increase in mixture porosity. A design methodology to address these characteristics is needed as the presence of relatively small amounts of mica content can severely impact the design of foundation elements in these soils. The most detailed case study comprising these soils is the Jamuna bridge site in Bangladesh where large-scale axial pile load tests were performed. In this work a back-calculation of the Jamuna bridge site considering API and CPT-based methods is undertaken and recommendations for pile design are proposed. Moreover, a comparison of pile load-settlement behaviour observed at the Jamuna Bridge site is carried out and applying additional adjustment factors on calculated shaft resistance in accordance with some of the methods is found to be advisable.