The influence of bitumen coating on the development of unit shaft resistance along driven steel and precast concrete piles resulting from subsiding surrounding soft soil (gyttja) induced by fill placement at terrain was investigated. All piles were instrumented with conventional discrete-point vibrating wire strain gauges and distributed fibre optic sensors to achieve high-resolution strain measurements. The magnitude of the mobilised unit shaft resistance along uncoated piles was observed to be primarily related to an increase in effective stress resulting from the dissipation of excess pore water pressures. The unit shaft resistance along bitumen-coated piles was found to be primarily related to the rate of relative movement between pile and soil, which highlights the effectiveness of bitumen coating in reducing shaft resistance.

This paper aims to analyze and describe the geotechnical behavior of a piled raft foundation of a tall building (53 floors, 172.4 m high) through the monitoring of strains in the building's columns and piles, the stresses at the raft-soil interface, and the foundation settlements. Field and laboratory tests were performed, and associated with axisymmetric and three-dimensional finite element analysis to the assessment of the measured data. The monitoring of the pile strains suggests the occurrence of soil expansion, caused by the raft excavation process, up to approximately 6 months after the excavation was completed. The presence of different soil profiles under the raft, with different mechanical properties, affected the distribution of the foundation settlements and the pile loads. Initially, the average pile loads were concentrated in the perimeter elements, but, as the construction of the building evolved, they tended to become more uniform. The effect of the superstructure stiff-ness caused successive load redistributions in the columns, which contributed to the maintenance of the maximum angular distortion of the building within the allowable values and reduced the load difference between the piles positioned in opposite soil profiles.