The shear layer that forms at the interface between a fluid in motion and a granular bed is shown to be tractable in the most general case, including the occurrence of flow separation from the grains, which appears to be the most common situation. The phenomenon of separation produces fundamental leading order effects, especially in relation to the mean flow between grains and also in the generation of a disturbed ensemble-averaged flow, which previous formulations were unable to detect. In this respect, we argue that some known results pertaining to the jet regime, recently introduced by the authors, can be directly extended outside that regime: in particular, the mean force that bed grains exert on the fluid, which appears to be generally applicable provided only that separation occurs. Furthermore, the maximum pressure disturbances, as well as the velocity disturbances at the outer edge of the shear layer, can be evaluated just as in the jet regime. This extension permits very general estimates of the main forces and the thickness of the shear layer, above and beneath the bed surface. In particular, the forces on the grains are shown to exhibit a spectrum. We present very simple expressions for the mean force as well as for the maximum force, which are compared with existing observations on sediment motion initiation under oscillatory flow, showing an excellent agreement.