Probing liquefiable soils by cyclic cone penetration

Soil liquefaction is a major concern for the design of geotechnical structures that involve sand or sandy soils. A steadily increasing number of case histories has been collected over the years, allowing the improvement of technical procedures adopted to detect liquefiable soils. Because of its repeatability, reliability and continuous data profiles, Cone Penetration Test (CPT) is one of the most widely used in-situ tests to evaluate the potential for soil liquefaction. The development of CPT-based liquefaction triggering procedures has progressed over the last decades and extensive studies have been conducted to provide empirical correlations between cone tip resistance data and soil properties.A new CPT prototype has been developed by the French company EQUATERRE and it aims to probe liquefiable soils by using a cyclic cone penetration instead of the monotonic penetration executed by standard CPT devices. At different depths, by setting target values of force and fixing the frequency, soil responses due to the applied cyclic loading can be studied in terms of displacements and forces evolution over time.This thesis aims to analyse the soil responses due to the cyclic penetration inside the large Grenoble Laboratory 3SR Calibration Chamber. The tested material is the very fine GA39 Fontainebleau sand and it has been studied in saturated dense (typically not liquefiable) conditions and saturated loose (typically liquefiable) conditions. Its physical and mechanical properties have been tested through a characterization and a triaxial testing programme. Because of the difficulty to deal with saturated loose sand, different sample preparation methods have been tested in small scale before performing tests in the large calibration chamber.In order to carry out a wider analysis, the results obtained through the cyclic CPT device developed by EQUATERRE have been compared with those one of standard monotonic CPTu penetrometer. Through the complementary analysis of cyclic results in terms of displacement vs time and force vs displacement, typical cyclic soil responses have been detected and critically studied in order to deeply understand the different liquefaction phenomena triggered by the cyclic CPT tests.