Construction Cost Estimating


Some useful guidelines to determine the depth of foundation for bridges

In this construction article, you can learn in detail how to find out the depth of foundation for bridges.

The depth of foundations for substructures depends on the safe bearing pressures of the soil after considering the impact of scour as defined in the proceeding paras. For bridges found in in-erodible streams, the foundations shall be safely fastened into the bed materials by setting up the foundation in it about one metre or so. The anchoring is generally provided with anchor bars.

The foundations for bridges should be developed across alluvium streams and taken down underneath the maximum scour level minimum one-third of the maximum scour depth from the H.F.L. and not under 2.0 metres for piers and abutments with arches and 1.2 metres for piers and abutments which provide support to other types of superstructure.

In most situations, the foundations should be taken down to such depths to maintain proper strength as well as perfect grip of the foundation.

It occurs for the following reasons:

The maximum scour adjacent to pier foundation should be 2.00 dm from H.F.L. So, the grip length for deep foundations should be 2/3 dm and depth of foundation from H.F.L. should be 2 2/3 dm = 8/3 dm.

To clear your conception, a solution is given to the following problem :-

Work out the linear waterway and mean scour depth when the design discharge is 1000 cubic metres per second and the value of silt factor is 0.8.

If the linear waterway is confined to 100 metres with two intermediate pier foundations containing average 2.75 metres obstruction to flow for each pier. You have to determine the mean scour depth as well as the minimum depth of foundation in every case.

To get the complete solution of the above problem, go through the following article

Some useful guidelines to determine the depth of foundation for bridges