Stress distrbution between Tanks 3

[pelelo]

Hello,

I am working on the settlement analysis of tank. There is an old tank about 15 m off this new tank.

Anyone knows if there is a ''rule of thumb´´ of how far can this new tank be located such that the stress influences from the old tank won´t affect on the new tank?

I know there are some charts about stress influences under circular loading (newmark, or Boussinesq) but some times this is somewhat time consuming.

Please let me know.

 

[BigH]

As a very simple rule of thumb, take a line at 2V to 1H from the edge of each of the tanks downwards and see where they intersect. if they intersect near a depth of 2B, then there is only a marginal influence (at this depth the increase of pressure du to the load is 10% or so). This is not time consuming . . .

 

[fattdad]

what's interesting to consider is the soil strength (and likely the corresponding modulus value) is different below the old tank. What you model from new-tank-geotechnical data may not be right for the conditions below the old tank. After all, it's realized a different stress history.

Boussinesq equations are pretty easy to use (spreadsheets) and can consider your exact case.

f-d

¡papá gordo ain’t no madre flaca!

 

[FixedEarth]

Maximum settlement case scenario is what BigH described, most likely scenario is what fattdad mentioned. A lot has to do with the soil stiffness in the upper 2B & overconsolidation ratio.

In the past, if the soils were layered, I used the Westergaard charts, instead of the more conservative Boussinesq solution. We are assuming both tanks are on nearly identical elevation & there are no descending slopes.

See the attached document & posted link for more insight:

http://www.geocomp.com/files/technical_papers/Criteria for Settlement of Tanks.pdf

http://www.FoundEng.com

 

[BigH]

fattdad is correct, of course, that the settlement under the load of the old tank has increased the modulus value for immediate settlements within its zone of influence.

For me, the suggested rule of thumb is to give a green-light/red-light estimate.

For tanks resting on clay, however, there may be problems associated with primary consolidation conditions. The old tank might have taken a clay into the virgin part of the curve wiping out any preconsolidation that might have existed (quasi-preconsolidation due to aging, for example (from secondary settlement) - and any new load induced by the new tank on the zone of influence under the old tank would experience virgin settlement (Cc)at once and under the new tank one might expect reconsolidation to pc' and then virgin consolidation. This is why experience is paramount.

 

[fattdad]

here's a good publication:

http://geotechref.coppernorthern.com/w/files/e/ee/Duncan_1987-DifferentialSettlements.pdf

f-d

¡papá gordo ain’t no madre flaca!