Cohesion is the component of shear strength of a rock or soil that is independent of inter-particle friction.

Apparent cohesion of soil means that the cohesion properties may be lost and it is unreal. In soil there are two kinds of soil cohesion:

1) true cohesion which is caused by electrostatic forces in stiff over consolidated clays.

2)apparent  cohesion which is caused by one of the following:

Negative capillary pressure (which is lost upon wetting)

Pore pressure response during undrained loading (which is lost through time)

Root cohesion (which may be lost through logging or fire of the contributing plants, or through solution)

Apparent cohesion is actually a suction force which is described with unsaturated soil condition. Bellow the GWL you have a water pore pressure and above suction with opposite sign. Although is usually assumed to be linear it is not, bu in general it stabilizes the soil and obtains greater capacity. For more I recommend you the Unsaturated Soils: Research and Applications or https://eunsat2016.sciencesconf.org/.

Thanks for your answers Dr Josifovski and Dr Ahmad.

Dear Cristiano,

In both cases we can speak about "apparent cohesion". But its origin is not the same.

In the case of soil improvement you describe, I think there is no relation between the apparent cohesion and capillary forces.