Different ways to compute settlements of footings

[oldestguy]

Hi Friends:

After viewing thread 256-19870 today I am wondering if it might not be interesting to compare different methods for predicting settlements of footings on two types of soil: sands and fine grained materials.

The reason I wonder is that I have used a method I seldom hear about. I've used it since 1959 when it was publicized. My experience has found that its use has been rather close to field measurements (where that could be done). It is from an August 1959 ASCE paper of the SM division Number 2135 by B.K. Hough. It had many discussion contributions, including Ralph Peck (who criticized it). However at least one discussor compared this method to actual settlement measurements and his results show it came out quite close.

If two typical cases could be compared, by different methods, perhaps tied to some actual on-site soils and measured settlement data, it would be interesting to see the results.

I'm thinking the work in steel mills by D'Apolonia (sp) might be some data to use. I do not recall where that was published, but seem to recall the Hough method compared well with his findings.

The Hough method makes some generalized assumptions that simplify the computations, but they seem to work for me. It is included also in his second edition of his text "Basic Soils Engineering", Ronald Press Co.

It is easily set up under a spread sheet program or it can be used in a dedicated computer program with the simple 60 degree approximation for load spread. I also use it in a compiled Basic program that runs on some computers that can run DOS.

 

[jheidt2543]

This is only a little off topic, but here are two references that may be of interest:

"Measured Performance of Shallow Foundations"
Edited by Miguel Picornel
ASCE Geotechnical Special Publication No. 15, 1988

"Predicted and Measured Behavior of Five
Spread Footings on Sand"
Edited by Jean-Louis Briaud nad Robert M. Gibbens
ASCE Geotechnical Special Publication No. 41, 1994

ASCE GSP No. 41 is particularly interesting; the experiment provided all participants with the same geotechical investigative reports and the footing sizes, the exercise was to predict the footing load capacity and settlement. They received 31 responses and some 22 different methods were used; none were Hough's method, but the experiment is very interesting to read. To have 31 engineers review the same data and make predictions for the same site and footings, then have them tested, gives a good insight into how others approach the same problem and their methods.

The most used method was Schmertmann's. The most used soil test data was the CPT; then SPT, PMT and DMT tests. "...it was not possible to identify the most accurate method because most people used published methods modified by their own experience or used a combination of methods."

 

[vulcanhammer]

For what it's worth, ASCE GSP 23 does the same thing for a driven pile.