Tecnologie innovative per il consolidamento di substrati di fondazione e opere geotecniche

The PhD research activities are focused on ground improvement application. The objective is to study the permeation grouting technique in granular soils and to understand the hydro-mechanical properties that can be obtained using non-conventional injection materials. During the project it has been developed an injection apparatus and a monitoring system of the grouting process that is used to study the permeation process and to develop a theoretical, and then analytical and numerical approach. Furthermore, the injection apparatus is used to simulate the permeation of different injection materials in soils and to generate specimen for hydraulic and mechanical evaluations. The experimental set-up comprises of a polycarbonate extruded clear tube, 50 mm in inner diameter and variable length (with a maximum of 1.6 m), and two floating caps at the extremities with a double sealing system. Once it has been filled with a selected soil it is inserted in a rigid steel chassis and the hole injection system can support 100 bar injection pressure. To simulate the soil micro-mechanical behavior has been created a loading system, composed by a screw that can apply a confining pressure on the soil sample. The column is then instrumented: • two load cells to control the confining pressure; • five pressure transducers to control the imposed pressure; • two pressure switches to impose pressure to the fluid; • laser ranging distance sensors to measure the flow rate; • vision camera to detect fluid front advancement. The data from the sensors are collected by employing Arduino processors and all the results are elaborated and displayed in real time with a Labview platform software. Some of the sensors were properly calibrated after being installed and all the measurements and the injection apparatus are validated before starting the test. The injection apparatus has been used to test different conventional and non-conventional grout with different rheological properties: sodium silicate, acrylic resin, colloidal silica, cement and micro-cement grout. For some of the previous injection materials have been defined a rheological time-dependent law. All these tests have been used to understand the permeation phenomena and to define an analytical and numerical predictive model that could be valid for all the soil in all conditions. By using this approach and by knowing the soil hydraulic properties, related to a new geotechnical project, it should be possible to indicate to designers the type of grout, the injection parameters and the injection geometry for this specific ground improvement application. Finally, a hydro-mechanical investigation of the different injection materials has been performed, consisting of the following test: permeability, unconfined compressive strength, triaxial test and brasilian test. For each injection test it has been evaluated the difference mechanical behavior from the bottom to the top part of the column, resulting from a variable soil saturation during the permeation process, that, in a ground with a grout spherical propagation, can be related to the radial distance from the injection point. Furthermore, a mechanical comparison, in term of friction angle and cohesion, is performed for the different grout types and, for some of them, at different curing time.