High-capacity ribbed pile foundations

This research concerns the influence of ribs on the ultimate capacity of a bored pile in overconsolidated clay. Ribbed bored piles are known to give increased shaft capacity in comparison to conventional straight-shafted bored piles. The investigation seeks to explore the effectiveness of ribs at increasing the ultimate capacity of a pile, and furthermore to understand how this enhanced capacity is derived. The scale pile test results are analysed using several industry standard methods. A plastic failure envelope for the base of the pile rib is identified. This plastic failure envelope is used to provide a detailed design solution for the ultimate capacity of a ribbed pile. The design solution is simple and requires a summation of the constitutive contributions from each rib and from the base and shaft of the pile. This method has been used successfully to predict the ultimate capacity of any pile tested to within ±8%

Forces involved with the extraction of casings used in rotary bored piling

Temporary casings are regularly used in the construction of rotary bored piles, to support the pile bore in potentially unstable soils and also to prevent water ingress from loose or water logged soils. The preferred method of removal of casing is by pulling with a crawler crane. However, the magnitude of force generated, particularly during the initial stage of casing extraction, is unknown. This paper describes a series of 50g centrifuge tests designed to model the casing and surrounding soil during extraction by crane. In each test different sized model casings were installed at various embedment depths into a layer of clay overlain by a well-graded sand to provide an array of data. The depth of granular overburden was varied from 60 mm to 120 mm to allow for assessment of the influence of this material on the extraction force whilst the casing sizes modelled 900 mm and 1800 mm prototypes

The London Geotechnical Centrifuge Centre at City University London

The London Geotechnical Centrifuge Centre located at City University, London is one of four currently active centrifuges in the UK. The centrifuge is well used and much of the geotechnical research at City University employs physical modelling but supported by a large element testing facility and numerical modelling capability. The centre was established in 1990 and the facility was extensively upgraded to provide more space for sample preparation and model making in 2004. In 2012 the centre is supporting 4 doctoral research projects in addition to visitors from China, Italy and UK. The focus of research is urban construction processes with an underlying theme of sustainability. Over the last 10 years the group has established a capability for tackling complex modelling problems and is currently investigating the application of smart instrumentation and control at high g