​The interaction between the solid particles and the pore fluid in granular materials affects various interparticle forces. The change in any one of these forces triggers the response of the granular skeleton, causes strain and even important fabric changes. Coupling phenomena that result in skeletal strains are related to fluid properties, electrical-chemical interactions, and thermal effects. The relevance of such couplings in-creases as the particle size d and the effective skeletal confinement σ' decrease, and well-defined coupling re-gions can be defined in the d-σ' space. Experimental results support order-of-magnitude estimates based on particle-level analyses.