Cohesion is the component of shear strength of a rock or soil that is independent of interparticle friction.
Some values for rocks and some common soils are listed in the table below.
During critical state flow of soil, the undrained cohesion results from effective stress and critical state friction, not chemical bonds between soil particles.
All that small clay mineral particles and chemicals do during steady plastic deformation of soft soil is to cause a pore water suction, which can be measured.
Critical state soil mechanics analyses the bearing capacity of soft clay on the wet side of critical state in terms of a perfectly plastic material with rapid undrained "apparent" cohesion.