Westergaard hydrodynamic pressure on bulkhead wall

[emilywalters]

See attached link for proposed calculation of hydrodynamic pressure acting on a bulkhead wall that is retaining alternating strata of low and high permeability material, and with free water against the other face.

I would like to know if anyone else has come across this kind of situation before. The two options I am considering for assessment of the wall at the moment are:

1) Calculate Westergaard hydrodynamic force acting from the top of the phreatic surface to the bottom of the lowest high permeability stratum.
2) Calculate individual pressures based on the distribution of Westergaard hydrodynamic pressures as indicated in the diagram (acting within the high permeability strata only). I am, however, unsure whether assuming the distribution is unaffected by low permeability strata is correct.

An additional point to note is that the bulkhead wall consists of long, large (1.2m diameter) tubular piles and shorter sheet piles. Would it be appropriate to ignore the hydrodynamic pressure on the tubular piles as a result of any strata below the toe of the sheet piles or is the general consensus that with a tubular pile of 1.2m it would be more appropriate to take cognisance of this pressure.

Any advice/opinions would be much appreciated!

#geotechnical #structural #ports #maritime #marine #quay

 

[Shu Jiang PEng SE]

The net hydrostatic pressure on the bulkhead wall depends on the water level deference inside and outside of the wall. You may need to determine the lowest ground water level outside the wall.

 

[JedClampett]

I've done some retaining walls, although not a whole lot of tied back sheet pile walls. But I've never taken into account any hydrodynamic forces. Everything is static. Soil, groundwater all of it. Even if the water was traveling at 2 ft/sec, it would only add a 10 psf force. And where would it be traveling? Through your wall?

 

[SlideRuleEra]

Agree with JedClampett, for the bulkhead shown, the magnitude of hydrodynamic forces (if any) is just "noise" compared with the magnitude of static forces and the accuracy of the necessary soil property assumptions.

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