Extension of the scour hole at bridge abutments.

Amir Reza Zarrati, Sepehr Karimi, S. Amin Salamatian

Thursday 2 july 2015

12:48 - 12:51h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering, Poster pitches

Parallel session: Poster pitches: 11B. River Engineering

In the present work, scouring around bridge abutments is studied. A flume 12m long and 0.76m wide was used for the experiments. The flume had a working section in the form of a recess below its bed which was filled with uniform sediment with median size of 0.95 mm. Abutments with rectangular sharp edged nose were installed in the working section and in both sides. In this way the bed topography when the scour holes of the two abutments overlapped could also be studied Experiments were conducted till equilibrium condition was achieved. Experiments were carried out with different contraction ratios and relative shear stresses. Relative shear stresses “u*/u*c” varied from 0.35 to 0.85 where u* and u*c are undisturbed upstream shear and critical shear stresses respectively. Contraction ratio defined as “L/B” ranged between 0.16 and 0.42, where L is the total abutments length and B is the channel width. Bed scour topography was measured by a laser meter. Results showed that the slope of the scour hole in upstream direction decreased with an increase in contraction ratio and flow intensity. The transverse slope of the scour hole also decreased with an increase in contraction ratio whereas it increased with an increase in flow intensity, whether the scour holes from the two abutments overlapped or not. Using the measured data, some relationships were developed for calculating scour hole side slopes at different directions around the abutments. Extension of the scour hole upstream of the abutments and at the bridge section can be estimated knowing the maximum scour depth and the scour hole slopes calculated from these relationships. Maximum scour depth can be calculated from one of existing empirical equations. An advantage of the present study is that if a pier is built in the vicinity of the abutment, bed scour depth at the pier due to the extension of the abutment scour hole can be calculated. The flow condition and bed topography at the bridge section at which the scour holes of the two abutments overlap and the bridge section experiences a full degradation can also be predicted.