Mitigation of Liquefaction Risk by Innovative Ground Improvement Techniques

The reduction of soil susceptibility to earthquake induced liquefaction is now considered a crucial issue in most of the seismic areas around the world, because it has been clearly seen that the damages on structures caused by the large reduction of effective stresses in the soil may overcome those induced by the inertial seismic forces. Several technologies have been studied over the years as countermeasures against liquefaction (e.g. densification and drainage, addition of plastic fine, cementation), but the most effective ones are usually not suited to be used in densely urbanised areas. Among the new-ly introduced mitigation technologies, Induced Partial Saturation (IPS) is con-sidered one of the most innovative and promising countermeasures, able to overcome this critical limitation. The goal of such a technique is to reduce the initial degree of saturation of the liquefiable soil just enough to reduce the pore pressure build up during the seismic shaking. Micro gas bubbles have to be generated into the water by air sparging (as done for environmen-tal issues), or by using environmentally friendly chemicals or even microor-ganisms that generate gas bubbles during their metabolism. Without entering into technological details, the lecture illustrates laboratory and in situ experi-mental evidence of the extreme effectiveness of IPS, introducing a sound and simple design procedure to be used by practitioners.