Tomas Sabaliauskas

The new testing scope of the old frictionless triaxial apparatus

Offshore wind turbine foundations episodically lose and recover stiffness as soil is disturbed during extreme events. Such sand behavior is not accounted for during standard testing procedures. Therefore, the following novel dynamic triaxial testing procedure is explored in this study: specimens are loaded past their peak strength and pulled back to initial length, where attempts to recover their initial stiffness are made by applying more loading cycles. This fundamentally changes how we view our specimens—they are no longer fragile and brittle. Instead, specimens can be axially compressed and pulled back to initial length many times as long as shear rupture and bulging are circumvented. Novel testing procedures were attempted using a frictionless triaxial apparatus. Frictionless triaxial is not itself a new concept, but the novel procedures revealed previously undocumented testing capabilities: (1) Multistage testing, wherein sand specimens can be liquefied (undrained), drained, and reliquefied (undrained again) many times, in one sequence, on one specimen; (2) Specimens can be compressed to large axial strain (15 % strain or more) and pulled back to initial length more than once. In the process, peak yield strength can be measured more than once at more than one density, all while using one specimen.