Is Westergaard's Hydrodynamic equation valid? 1

[Sam002]

Im analysing a caisson structure. the hydrodynamic force on the caisson structure obtained from the transducers installed on it is much much higher than the theoretical value given by the westergaard's equation. can anyone please tell me why people still use westergaard equation for construction at port and harbor facilities? Do they use high factor of safety to account for the actual condition?

 

[VoyageofDiscovery]

What event occurred or is it just wave action that was monitored?

 

[Sam002]

the earthquake caused the wave which ultimately exterted pressure on wall

 

[VoyageofDiscovery]

Was there soil directly behind the wall?

 

[Sam002]

yes there is soil directly behind the wall on landside and ocean water on ocean side.
the soil also has pore water in it. Now is there is an earthquuake, will the ocean water pressure on wall, soil pressure on wall, pore water pressure on wall be in same phase with earthquake acceleration or in opposite or some of those in same phase and some in opposite?

 

[dgillette]

That's not a simple question, as it depends on the relative stiffness of wall and fill, freq content of the EQ, etc. If the wall is "stiff" (such that its natural frequency is high with respect to that of the fill), the soil and ocean water pressure will be out of phase, such that the fill and its pore water - think in terms of undrained soil behavior because of cyclic loading with high frequency - are being left behind by the wall when the wall is pushing into the ocean. (That is, the hydrodynamic pressure is highest when the fill pressure, which would help resist it, is lowest.) It gets more complicated if the wall is higher and more than just the principal mode of vibration is excited, but that's probably not a big issue for most structures.

One question that occurred to be but I can't answer is To what extent you can take advantage of the very short duration of loading from each cycle? Can you allow for momentary yield a few tenths of a second without failure of the structure? I can't comment on the validity of Westergaard either, but I've never seen anything to replace it.

Regards,
DRG

 

[himat42]

sam002

It appears that you case looks like Quaywall.
If I recall, there are few papers published in "Soils and Foundations"(Japanese journal). There may be some ASCE Special publications.

Regards,
HTS

 

[VoyageofDiscovery]

How are you able to extract from the failure that the hydrodynamic is the culprit?

Earth pressure has a dynamic contribution as well.

VOD