Abstract

Piles have been used for thousand years as foundations for human dwellings and they are nowadays still used with the same scope. Piles can be either driven or cast in-situ, the choice of one installation method relative to the other depends largely on the characteristics of the soil on site and nonetheless on urban and environmental conditions such as the presence of nearby buildings and houses. The installation methodology affects costs and times involved in the project as well as the pile behaviour during subsequent loading. Amongst those, the jacking technique is becoming a standard for installing driven piles, in particular in urban areas due to the low noise and vibrations involved in the procedure. Jacked piles are pushed into the ground by a static force mobilised against the reaction force of previously installed piles. A series of centrifuge and calibration chamber testing has been performed in order to assess the stress field around jacked piles during and after the installation. A particular jacking technique, called surging, was also investigated in order to reduce the shaft load experienced by the pile during jacking. It is believed that the method can reduce effectively the installation loads of open-ended piles installed in hard grounds. Finally, a new technique for stress measurement is presented. A new type of stress sensors was developed at the Technion University in Israel and implemented in the geotechnical centrifuge in Cambridge. Results show that measurements taken by these new sensors are not affected by soil type, density, soil stiffness and previous stress history.