Effect of laboratory sample-reconstitution method on the stiffness, strength parameters and envelope of cement-mixed silts

Stiffness and strength of cement-mixed soils are usually evaluated by means of laboratory tests performed on specimens reconstituted in the laboratory by dynamic compaction. Dynamic compaction of specimen can be achieved by employing different compaction energies, anyway, none of the available methods realistically simulate the construction of geotechnical structures of cement-mixed soil. Differences between in situ and laboratory procedures (not considering humidity and cement percentage control and other environmental aspects) mainly concern: - type of loading (dynamic or quasi-static) and stress-path - sequence of loading from structure formation to the working conditions More specifically, the use of gyratory press to reconstitute soil specimen seems to reproduce more realistically the stress-path during in situ soil compaction and those induced, subsequently, by working loading (i.e. traffic loading). As For the sequence of loading, it has already been pointed out the importance of applied pressure during curing time by several studies. This paper compares the strength of a cement-mixed silt reconstituted in the laboratory with different methods (Standard Proctor, Modified Proctor, Gyratory Press). Moreover, most of the specimens have been cured for 28 days under 100% humidity at temperature of 22 but some of them have been cured under sustained consolidation pressure. Specimens were sheared in monotonic loading triaxial compression. The results clearly show that strength increases with compaction energy reaching its maximum in the case of specimens reconstituted by means of Gyratory Press. The effect of sustained consolidation pressure is also very clear. Effects of the stiffness are not so evident because of influence of equipment compliance.