Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio
Résumé
This paper presents new data on scour around a vertical pier in cohesive
soils. It specifically focuses on the temporal evolution of local scour hole
around the pier with increasing the clay/silt ratio content. Series of flume
tests were performed using soil mixtures made with 85% fine sand and
15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite
clay, and various combinations of both with different proportions. The
water velocity during the tests was kept constant and slightly above the
erosion critical velocity of the fine sand used in the mixtures. A 3D laser
scanner was employed to continuously record the geometry of the scour
hole. Results show that increasing the Kaolinite clay in the fine fraction
reduces significantly the scour. The mixture with a range around 7.5–10%
of kaolinite clay fines content provides the threshold composition for cohesive
soil behaviour effect in scouring process, recognized through scour
pattern change. As the clay content increases, notable reductions are
observed in the dimensions of the scour hole. Furthermore, the temporal
evolution of maximum scour depth measured in flume was in agreement
with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion
Function Apparatus) method.