Burial of short cylinders induced by scour under combined waves and currents

Results of an experimental study of the scour and burial of cylinders placed on a sandy bed under the combined flow of regular waves and currents are presented. Experiments were conducted for cylinder Reynolds wave number and Keulegan-Carpenter number within the ranges 1.5 × 10⁴ ≤ R_c ≤ 1.2 × 10⁵ and 2 ≤ KC ≤ 48, respectively. Analysis of the observations indicates that existing semiempirical formulas for prediction of equilibrium-burial-depth and time scales for pipelines are not suitable for the case of a cylinder having a finite length. Thus the need for developing new expressions for both final-burial-depth and time scales based on new observations. In these experiments burial depth shows stronger dependency on the Shields parameter θ than on the KC, whereas burial-time scales seem to be influenced by both KC and θ. A new empirical predictor for estimating the equilibrium burial of short cylinders under combined flows is presented. The equation is based on the combination of θ, KC and the ratio of current velocity to the effective wave plus current velocity.