Experimental study on time factor of scour around pile groups

Pile groups are widely used in hydraulic and ocean engineering. They may suffer serious threats from long time scour process during constructions and operations. Time factor is crucial to predict this long duration process. However, mostly previous studies on time factor are proposed for single pile and pipeline, limiting the application effectiveness in pile groups. Previous researches focus on scour under threshold velocity intensity and cannot be directly applied in live bed condition. To expand the velocity intensity, flume experiments are conducted with uniform quartz sand in clear water and live bed condition. With selected experimental data from literatures and data of present work, an improved time factor taking velocity intensity and equivalent width of pile groups into consideration is proposed and verified, proving that this new time factor can make a reliable prediction of scour process and equilibrium scour depth with short duration for both single pile and pile groups. Another time factor with three exponential functions is also proposed for interpolating, which produce good performance from literatures. All experimental data mentioned above shows that the former optimized method is a reasonable predictor of scour depth around pile groups and the later method is applicable to interpolating. •Experimental studies on scour around pile groups in clear water and live bed conditions.•Improved time factor taken velocity intensity and equivalent width of pile groups into consideration shows good performance.•New equation of time factor for interpolating experimental data.•Present work verifies that live bed scour depth around pile groups is smaller than under threshold velocity intensity.