The design of protection dams against snow avalanches is still based on empirical methods that should be improved to optimize structural countermeasures. Many experimental investigations on gravity driven flows interacting with an obstacle were performed during the last ten years, particularly in the framework of European projects Cadzie and Satsie. The main objectives of these investigations were to develop the scaling laws governing the interaction between snow avalanches and defences structures. Most of the experiments were carried out on small-scale laboratory experiments involving dry granular material to simulate dense snow avalanches. Some additional experiments were conducted in the field with real snow flows and using larger scale devices. The experimental set-ups that were used consisted of a free surface gravity driven flow down an inclined chute and impacting an obstacle. Depending on the geometry of the set-up, steady flows conditions or transient run-out spreading of an avalanche were analysed. This paper gives first an overview of the main results concerning (i) the zones of influence of the obstacle (dead zones, granular jumps, and downstream jet), (ii) the stresses exerted by the flow on the obstacle and (iii) the avalanche run-out shortening due the obstacle. Then we try to show that a simple phase diagram (incoming Froude number versus obstacle height relative to the incoming flow depth) allows defining flow/obstacle interaction regimes. Finally we discuss the dimensioning of dams against dense snow avalanches.