Crushed Stone Ringwall for 102 m Diameter Oil Tank 1

[VANayak]

Hello Everyone,

I recently joined this forum.I have a question. I am designing a crushed stone ringwall foundation for 102 m diameter 24 m height EFR tank cone bottom .
I did a bearing pressure check for the ringwall . The ringwall is 1.3 m above grade and 2 m below grade. Slip Failure analysis was done by an geotech expert and he recommended to go 2 m below the grade.

My question is for bearing pressure check I am getting negative pressure due to the eccentricity of the tank loads acting on the ringwall bottom. The ringwall bottom is 12 meters wide. Since this is the first time I am designing a crushed stone ringwall foundation and that too for such a huge diameter tank, I wanted to check if my approach towards this calculation is correct or not. Attached is a picture of the loads I have considered.

Any help would be appreciated.

 

[oldestguy]

I could be wrong, but this same subject project was in a post recently. My memory for that post was the soil conditions showed potentially some significant settlement likely. In any case for this post I suggest getting back to your geotech since,with many factors not provided, you will not get the best answers here and possibly they will be misleading answers. Double posting for this forum is frowned upon also.

 

[oldestguy]

Here is an example as to why you don't differ from recommendations of an expert. At an electric generating plant under construction a cooling water pond had to be dug. It was near a railroad main line. During the excavation, some sections of the adjacent railroad sank significantly as supporting soil was somewhat undermined by the pond excavation. The railroad construction engineers (not train drivers) had never built any railroads in their lives. So they called me to ask as to what to do. I said fill the area back up to grade and then go 5 feet higher. After one month (if time permits) remove that extra fill and install the track. About two weeks later I get a call saying they built it back to grade and installed the RR tracks. However, shortly thereafter the whole filled area and the tracks settled again significantly. Not following my advice they had a lot of extra work and expense. In the subject case, a much greater loss might occur by not following the geotech advice.

 

[Mad Mike]

I must echo OG's sentiment - you're constructing an enormous structure which I suspected is on reclaimed land over a deep soil profile. If you're working to API standards you are constrained by extremely tight differential settlement tolerances; your bearing pressure check has no meaning in the context of these limits.

Without anything to go by, I'd want to see that structure on more than just a stone ring-beam; settlement-reducing piles are infinitely cheaper than a failed tank of the size you're talking.

All the best,
Mike

 

[VANayak]

Thanks.

Yes, the Geotech expert has done settlement calculations where the settlement is 290 mm at the center of the tank and 170 mm at the edge of the tank.
The tankage team confirmed that they are OK with these values.
The geotech expert also did a Slope Stability Analysis by Slip Circle method.

Sorry I did not know there was already a post about this topic. Could you please send a link of that post.. I am not able to find it.