Seismic upgrade of existing structures and earthquake-resistant foundations using self-drilling micropiles

抄録

The seismic upgrade of existing structures and the construction of earthquake-resistant foundations is a very current task in seismic regions worldwide. The use of composite tubular self-drilling micropiles allows simply and effective solutions also in very confined sites. Using this technology, the hollow bar simultaneously acts as drilling rod, injection tube and reinforcement for the micropile and can be used in any type of soil. This is a composite micropile: steel with a continuous thread and cement grout body just like reinforced concretes. Thanks to the very high skin friction between grout body and the ground this is a low settlement system which has an excellent behavior under seismic forces transferring a big percentage of the inertial forces to the ground. By using hollow steel loadbearing elements of several dimensions and designing the pile to transfer the forces to the ground, it is possible to install micropiles with many design loads, even for 2.000 kN and more. Former investigations and numerical simulations have shown the positive behavior of groups of inclined micropiles under seismic actions and possible liquefaction problems in comparison to big and massive piles. The paper presents the main features of this technology and illustrates a significant project carried out that highlighted the advantages of the system.