STADYN Wave Equation Program 7: Revision of Soil Properties (Results)

In the last post we discussed the change in cohesion in the $\xi-\eta$ interpolation. Now we apply these to the program to see how they change the results.

In the original study there are three test cases, as noted here. For this stage the first and the third will be considered. The results for the second (after adjustments for changes in the $\xi-\eta$ interpolation) are little different from before; we will consider major changes to impact that case in our next round.

That leaves the first and third. For the first–comparison with a static load test–it was necessary to readjust the values for $\eta$ to reflect changes in the meaning of $\eta$ relative to soil properties, as discussed in the last post. The changes made resulted in layering with the following characteristics:

Layer	Bottom y-coordinate, m	$\xi$	$\eta$
1	5.18	-1	0
2	7.32	-1	0
3	15.2	0.5	0
4	30.5	0.5	0

The static load test results can be seen below.

Comparison with the original study show little improvement in the failure load correlation; however, the load-deflection relationship before failure is significantly improved. The system was much softer in the original study and the improvement reflects the better estimate of the elastic modulus. The blow count is very similar to the original study.

Turning to the inverse case that was also discussed in Warrington and Newman (2018), based on the previous results, it was decided to drop consideration of 1-norm results. The results are reproduced in outline below for the three cases run (refer to Warrington and Newman (2018) for details.)

$\eta$ Limiting	Difference Sum	Static Load, kN	Average Shaft $\xi$	Average Shaft $\eta$	Toe $\xi$	Toe $\eta$
+-1	0.0034	673	0.084395	-0.46825	-0.992	0.758
+-2	0.00327	449	-0.455	-1.3375	-0.57	-0.727
+-3	0.00143	269	-0.26775	-2.1775	0.113	1.12

Comments:

The difference sum for the highest $\eta$ variation was the best match we have obtained to date for this case; the velocity match is shown below. The situation around L/c = 1.5 is still difficult but the rest of the correlation is improved.
The static load decreases with broader $\eta$ variation and a lower difference sum. This is different than Warrington and Newman (2018), where the static load “settled down” to a close range of values.
The plot above does not reflect that, on the whole, the variation of $\eta$ along the shaft was less than experienced in the past, especially with the +-3 run. The stratigraphy of the site suggested relatively uniform soil properties along the shaft, and this is beginning to be seen in the inverse results.
The +- 3 run was very heavily “toe weighted” in resistance.

While both of these cases show progress, the time has come to consider the whole issue of pile-soil interface issues, which will be considered in our next updates.