The major problem is that base slab is already 2 m thick. Still, the shear force is very high and need more shear reinforcement. Can anyone suggest some ideas on how to provide shear reinforcement on 2m (or even thicker) base slabs.
If the slab has not been built yet, some micropiles can be drilled along the contact surface of the slab with the ground, as shear anchors. Another variant may be to add a notch or heel at the base of the slab, as a shear key.
Even if the slab is already built, the piles can be applied, drilling from the top surface.
Depending on the circumstance, such as piers located along the outer margin of a channel bend, you might look into J Hooks or Cross Veins, which would move the thalweg away from the outer bend toward the channel center and reduce shear stress along the bank. David Rosgen has a paper on this use at wildlandhydrology.com. For larger rivers, David Derrick has designed some bank barbs designed to reduce bank stress and might help reduce stress on piers near the banks. There have been some studies on bridge scour, and I think I remember one from South Carolina by USGS. If I run across it, I will followup. Just a note, if the bridge cross section and fill has narrowed increasing velocity and potential for degradation, properly placed cross vanes can not only control bank stress, but also may be added to provide stable grade control to limit degradation.
[I am just rewording William F. Hansen response.]
Instead of a gigantic concrete slab, you may redesign the geometry such that the shear stress on the slab becomes lower. It depends on the structure. If it is a bridge in bend think to "river training structures" such as spur. If it is a spillway or outlet of culvert, think to a hydraulic energy dissipator. Think to adding the roughness with rock protection. So somehow reduce the speed. In some cases building a check dam or plunge pool downstream can increase the depth and reduce the speed.
Look at HEC 23 by FHWA for design guidelines and examples:
https://www.fhwa.dot.gov/engineering/hydraulics/pubs/09111/09112.pdf
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