AN INSIGHT INTO THE SETTLEMENT MECHANISMS OF RUBBLE MOUND BREAKWATER ON MUDFLAT USING DEM

Because mudflats are compressible, substantial settlement will occur during construction of a rubble mound breakwater at such a site. The use of geosynthetics as reinforcement is common during breakwater construction [1]. A suitable numerical model should be selected to provide insight to the mechanisms of settlement of such a reinforced rubble mound breakwater. Although numerical methods based on continuum mechanics have been used to model the behavior of embankment systems, they cannot provide insight into settlement because they cannot approximate the individual movement of the particles. Rubble mound breakwaters consist of rockfill, which is naturally discontinuous (Figure 1). Moreover, basing the numerical method on discontinuum mechanics to simulate the behavior of rockfill has not been achieved. The aim of the current study was to evaluate the control mechanisms of settlement of rubble mound breakwaters and the effect of geosynthetics on their performance. A full-scale case study of a rubble mound breakwaterconstructed on soft soil is considered for which the effect of the pattern, size and number of layers of the geogrid on performance was monitored. A series of numericalsimulations using the discrete element method were done to evaluate settlement caused by submersion of the particles into the seabed. The effects of geosynthetic parameters such as stiffness, number of layers and length of geosynthetic material were analyzed. The results showed that the submersion of the individual particles of rockfillinto the seabed is the main mechanism of settlement in an unreinforced breakwater (Fig. 1). This value is higher than for classic settlement (elastic or consolidation) [2]. However a reinforced geogrid acts as a separator and prepares a continuous base for the rockfill to prevent individual movement. Classic settlement is main mechanism of settlement which controls the behavior. It was shown that the length and number of geogrid layers had greater influence over decreasing settlement than the tensile strength of the geogrid.