Behaviour of reinforced polyurethane resin micropiles

This paper deals with the field behaviour, under tension and compression, of an innovative kind of micropile made from reinforced expanded polyurethane resin. Micropiles were installed in various sample sites characterised by the presence of silty-clayey soils. In order to analyse the frictional resistance of a single micropile and to determine the bearing capacity in different conditions, a series of field load tests was carried out. The method of construction of the micropiles and the execution of field tests are briefly described. On the basis of the field tests, a method to evaluate the ultimate load was defined. Moreover, the micropile-soil mechanical interaction was modelled by applying a simplified analytical solution of the load-displacement behaviour. The obtained results provide a useful support in the evaluation of both the serviceability and the ultimate design capacity of the investigated micropiles. The most innovative aspect of this technology lies in using less costly equipment than required for other pile types, with machines of reduced dimension, which can be very useful for underpinning works in restricted spaces under existing buildings.