a few questions

[Marissa]

1. In Problem 54. The answer is 1.643 (A) using the round up number (qmax) 5400 during the calculation. However, I got 1.652 (B) using qmax 5371. Hopefully, such close answers won't be shown in the real exam.

2. Problem 58, the final step is to get factor of safety. Why the actural (net) bearing pressure in CERM equation 36.23 is not used in the denominator?

3. Problem 62. From CERM Figure 38.1, sigma h is the same below the critical depth (10B-20B). Why the solution get the stress along the whole pile lenth.

I appreciate your time and effort for clarifying these.

 

[Daisy]

1. In Problem 54. The answer is 1.643 (A) using the round up number (qmax) 5400 during the calculation. However, I got 1.652 (B) using qmax 5371. Hopefully, such close answers won't be shown in the real exam.
2. Problem 58, the final step is to get factor of safety. Why the actural (net) bearing pressure in CERM equation 36.23 is not used in the denominator?

3. Problem 62. From CERM Figure 38.1, sigma h is the same below the critical depth (10B-20B). Why the solution get the stress along the whole pile lenth.

I appreciate your time and effort for clarifying these.

I'm just now getting the problems you've referenced.

1) I believe on the PE exam you would be fine with the answer you calculated

2) You're asked to find the ratio (FS) between the actual pressure and the allowable pressure. You calculate the net and allowable pressures (as designed) as shown in the solution, and then divide it by the actual pressure as calculated as Pmax/Amax, which is what is shown in the solution. Does that make sense?

3) I'm struggling with this one too. Can you tell me why the average depth is used to determine the overburden?

Thanks

 

[Civ_Guy]

For your question Number 3, you are dealing with clay (instead of just sand) starting above the critical depth, (using 15B from Das Foundations book, 2nd ED), therefore lateral earth pressure does not max out at the 15B depth. It must be calculated until you reach the driven depth, since your dealing with clay.