The paper focuses on the process of wetting-induced compaction in unsaturated soils. While such forms of irreversible deformation are referred to as collapses, a mechanical interpretation based on concepts of material stability has not yet been provided. Here we use a critical state plasticity model and an expression of second-order energy input accounting for changes in fluid pressures and/or volume fractions. Soaking-induced compaction is then simulated and interpreted in light of the controllability theory. Our results suggest that wetting-compaction is not necessarily associated with the loss of uniqueness of the incremental response. Compaction is indeed predicted not to be controllable only in soils that undergo considerable plastic strains upon wetting. In these cases, plastic models wiThenhanced hydraulic hardening predict the possibility of a loss of control of the water injection process, according to which the applied stress is no longer sustainable because of the degradation of the mechanical properties.