Laboratory investigation on pore pressures inside a rubble mound breakwater in depth-limited waters

Abstract

The present paper reports the analysis of pore pressure measurements acquired inside a small-scale conventional breakwater during an experimental campaign performed at the EUMER laboratory of the University of Salento (Lecce, Italy). The new data are used to investigate the effects of depth-limited water conditions on the wave-induced pressures in a porous structure in front of a 1V:30H foreshore. Specifically, the paper addresses and discusses the impact of the relative depth on three aspects: the frequency response of pore water pressure in the structure, the energy dissipation through the cover layers and the pressure attenuation inside the breakwater core. Additionally, the paper includes a comparison between the experimental results and the empirical models actually available in literature, able to predict the reference pressure at the armour/filter layers interface and the pressure damping inside porous structures. Results firstly show that shallow water conditions amplified the influence of wave long components on breakwater response to wave action, inducing a pressure attenuation inside the structure of about 80%−90%, mostly between the armour and the filter layers and highly dependent on the wave period. Instead, the comparison with the empirical formulae shows that the predictive models considered in the present work generally underpredict the damping coefficient, especially in intermediate/shallow water conditions, demonstrating that the relative depth has a high influence on both the reference pressure and the damping coefficient.