Help With PE Example Problem 1

[MarieBarnes84]

Hello,

I am finishing up preparing for the Civil PE in Geotech and this example problem has left me a bit stumped (see attached).

I know that you have to equate uplift forces to the weight of the concrete and the bond resistance, however the solution doesn't state how they come up with certain input parameters.
P[sub]u[/sub] = 62.4 x 20 x 9 x 1.5
W[sub]c[/sub] = 150 x 20 + (2 x 1250)

Any guidance on how the value of 9 as an input parameter was determined would be very helpful.

 

[CarlB]

Looks to me the calcs don't match the figure.
The calcs would make sense if was 20' vs 60' between the walls, as 20 is used in both calcs.
Also, water table 9' above base vs 60' in the figure.

With the dimensions given, I get 30' concrete required, which would be nuts.
With 20' space and 9' submergence, I get 3' thick.

 

[MarieBarnes84]

Carl, thank you for the confirmation. I don't believe the given solution and the given information in the problem are accurate.

 

[PEinc]

According to the sketch, water inside the cofferdam is at the top of the tremie. Assuming that the 1,250 lbs per side is per VF of tremie per LF of cofferdam and that the 60 feet to bottom of submerged tremie is correct, I get T = 25.2' which is still significant. See calcs. If this were a real design situation, why not drive SSP deeper to prevent boiling and eliminate the tremie seal?

http://www.PeirceEngineering.com