A series of load tests have been performed on instrumented 762 mm dia. tubular steel piles driven into low to medium density grade A/B chalk at St Nicholas at Wade, Kent, UK. This paper presents the results from the static axial uplift tests, which were performed on two piles 7, 50 and 120 days after installation in order to investigate the time-dependent variations in shaft resistance. The results show that the static ultimate shaft resistance of this type of chalk can increase by up to a factor of seven over this time period, as a consequence of ‘set-up’ effects. The test results also show that the ‘set-up’ effect is reduced if the pile is subject to lateral loads up to 50% of the ultimate lateral capacity before uplift loading, while the application of lateral loading up to 10% of ultimate lateral capacity had negligible influence on axial capacity. The measured load distribution from strain gauges suggests a mobilisation of larger unit shaft resistance in the lower half of the pile. This paper also describes the geotechnical site conditions, the pile instrumentation and the effects of pile driving on the chalk.

This paper presents results from a preliminary testing campaign to explore the feasibility and benefits of performing cyclic cone penetration tests with measurement of pore pressure (CPTu) in chalk. The CPTu's cone is a miniature driven pile and this technique permits the monitoring of degradation of sleeve friction and pore pressure development during cyclic loading. It was found that while consistent degradation of measured sleeve friction takes place within a few cycles, this was not associated with an observed pore pressure build up. However, uncertainties about the pore pressure measurements arose because the remoulded chalk next to the cone was probably unsaturated and also the pore pressure transducer was positioned close to the tip of the cone. Analysis of the results suggests that the technique may have promising potential to increase understanding of the underlying mechanisms and aid the design of axially loaded driven piles in chalk. Nevertheless further validation and development would be necessary in the future.

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. instrumented piles driven into chalk. The testing campaign comprised the performance of both monotonic and one-way cyclic lateral load tests, performed at different times after pile installation.The tests were performed on five piles with uniform outer diameters of 762 mm and embedded lengths of 4 m and 10 m, in order to investigate the difference in response between short and long piles.Lateral pile head load-displacement behaviour to failure has been analysed. The tangent stiffness evolution during monotonic loading has been evaluated at different times after pile installation and the chalk set-up has been found to have no effect on piles behaviour under lateral loading. The pile secant stiffness during cyclic lateral loading is also investigated. Accumulated pile head lateral displacements are discussed and their pattern is described by a logarithmic function that varies with number of cycles. The creation of a gap between the chalk and the pile during cyclic lateral loading was observed, which influenced the shape of the load-displacement loops. The influence of the instrument protection system was taken into account in analysing the results.