| Determination of the local scour depth around bridge piers in soils is one of the most important problems in the design of bridges over water. Failure of the foundation due to scour does not occur when the depth of the foundation is greater than the local scour depth. Most of the previous investigations to predict this scour depth concentrated on non-cohesive soils. The equations or methods developed for local scour around bridge piers in non-cohesive soils do not give reliable predictions for cohesive soils.;Systematic investigation was done by conducting a series of experiments in 0.45m-wide and 1.5m-wide flumes on various soils including Porcelain clay, Armstone clay, Bentonite clay, and sand to study the effect of soil types, pier diameter, water depth, and flow velocities on the scour hole development. Two theoretical models, the hyperbolic model and the exponential model, were developed to extrapolate the measured data to give the ultimate scour depth. A methodology called SRICOS was developed in order to predict the scour rate around bridge piers in cohesive soils. The validity of the methodology was evaluated by comparing with the experimental results.;The results obtained from this study indicate that: (a) the water depth has negligible influence on the ultimate scour depth, (b) the ultimate scour depth in cohesive soils is equal to the ultimate scour depth in non-cohesive soils, (c) the rate of scour in clay is considerably small compared with that of sand, (d) Froude number has a weak influence on the scour depth when compared to Reynolds Number, (e) the maximum scour depth occurs either in the back or on the side of the pier in clay, (f) scour history has some influence on the scour due to the present flood.;The application of SRICOS developed in this research is limited to the laboratory flow conditions. Therefore, this methodology should be compared with the field data before considering it as a general methodology applicable for all types of cohesive soils. |
