Abstract The increasing interest in the undrained cyclic behaviour of unsaturated soils is justified by the evidence of the beneficial effect of desaturation on liquefaction resistance and is thus strictly connected with the need to put forth sound tools to be used in the design of Induced Partial Saturation (IPS) interventions. IPS is still far from being a routine technology because of the lack of such design tools, as well as of simple technologies to obtain and preserve it on site. This paper offers a contribution to the first issue, based on the energetic interpretation of laboratory results that highlights the role of the volumetric and deviatoric components of the specific energy spent during undrained cycling on the liquefaction mechanism. Independent experimental results taken from the literature are successfully simulated using this interpretation. Then, stemming from the theoretical and experimental considerations reported in the first part of the paper, two possible approaches to calculate the desired degree of saturation of a loose sand (design goal for IPS) are introduced and discussed.