A NUMERICAL INVESTIGATION OF THE INFLUENCE OF FRICTION AND VIBRATION ON LABORATORY SCALE ARMOUR UNIT LAYERS

The design of coastal structures armoured with concrete units relies heavily on hydraulic stability results obtained in scaled laboratory flume tests. Surface friction effects are known to be important but remain poorly understood. The geometric configuration, force interactions and internal stresses taken up by units in the model construction process will depend on resistance to surface sliding which can be approximated by a Coulomb type friction coefficient, mu Similarly, further settlement, compaction and internal stressing of units during wave disturbance are considered likely to be affected by mu Surface textures of painted, plastic and mortar units may vary considerably. A range from mu = 0.3 to 0.9 or above is sometimes suggested. Contrary to real structures, at the scale of laboratory models, contact damage and interpenetration of units is negligible and frictional elastic unit behaviour is a realistic assumption for an analysis of dry unit interactions. New numerical simulation technology is used to investigate settling, reserve stability of contacts, static and dynamic stresses in 20-unit packs of 0.008m(3) CORELOC (TM) and ACCROPODE (TM) units for a range of friction and vibration amplitudes at a length scale of one tenth prototype scale. When compared with their equivalent 1:1 prototype scale simulations, on average, results are broadly self-consistent: peak dynamic stresses scale approximately with square root of the length scale while static stresses scale with length scale. Peak static stresses can vary greatly between apparently similar units and packs.