It is widely accepted that critical properties of geo-materials that play a key role in failure of earth-structures undergo often a substantial evolution induced by non-mechanical processes and variables. That includes: hydro-thermal fracture, thermal collapse, chemical mass removal or accretion (dissolution or precipitation), chemical shrinkage/swelling, drying shrinkage, capillary force evolution during pore water phase change. The properties affected are: strength in all its manifestation, compressibility, permeability, thermal conductivity, to mention just a few. The physical processes involved are either natural or engineered. Their phenomenology is per se a conundrum, as often they constitute a series of parallel or sequential processes. A review of several phenomena leading to geomaterial degradation, and methodology is presented to deal with multi-physical couplings in constitutive modeling. In plasticity, the central constitutive function is a hardening rule. Also in this case, phenomenological observations indicate a chemo-mechanical, two-way coupling. Other degradation phenomena discussed include drying—cracking, and or the role of suction induced hardening in unsaturated materials.