Foundation, Concrete and Earthquake Engineering

How can bearing capacity of shallow foundation be determined from permissible settlement?

This post concerned with plate bearing test. At first we have to know what plate bearing test. By this field test ultimate bearing capacity of soil and its settlement under designed load can be determined. In this test a steel plate is loaded at foundation level and settlement respective to load increment are recorded. The loads are gradually increased until the steel plate sinks at rapid rate. The ultimate bearing capacity of soil at foundation level is determined by the load at which plate sinks rapidly divided by area of steel plate. As we know, safe bearing capacity is a fraction of ultimate bearing capacity. This fraction is call factor of safety.
load-settlement curve from plate bearing test
A plot, known as load-settlement curve, on logarithmic scales (log-log plot) are done with load intensity as ordinates and settlement values as recorded in test as abscissa. In the plot two straight lines are found. The yield value or yield point is determined from intersection of two lines. This yield point is important in this discussion.

Now question is how to use this value. We realized, so far, in this discussion that safe bearing capacity is closely related to settlement of footing. The above load settlement curve provides ultimate bearing capacity and hence safe bearing.

The load intensity corresponding to yield point is the ultimate bearing capacity. From which using factor of safety 2-3 the safe bearing capacity is determined. This is safe bearing capacity for settlement.

The actual safe bearing capacity should smaller of following two:

a. Safe bearing capacity from settlement as derived from load-settlement curve.

b. Safe bearing capacity on the basis of shear failure

1 comment:

  1. Thanks for sharing your expertise and experience with us