Soil fracturing of soft silty clays for the reinforcement of a bell tower foundation

Soil fracturing is a rather recent technique for soft soils reinforcement. For many years, grouting in fine-grained soils has been a recurrent challenge for geotechnical engineers. Very different injection pressures can be reached depending upon relevant over consolidation ratio, injection rate and grout viscosity. In general, two alternative soil responses can be observed: cavity expansion or soil-fracturing. In the paper, data from a well investigated field study are reported, in which extensive soil fracturing was carried out in order to improve the mechanical characteristics of the very soft silty clay underlying the second tallest bell tower in Venice. To this purpose, a lay-out of about ninety 12 m-deep injection pipes was installed into the subsoil all around the bell tower foundation and each 50 cm-spaced valve was injected 3 or 4 times with a suitably cali-brated cement-bentonite mixture. Data analysis from a rather detailed experimental programme of in situ and laboratory soil testing together with carefully recorded injection parameters enable to better understand the mechanisms of soil fracturing at real scale.