ERRATA - Goswami's Practice Exams (New)

[ptatohed]

There has yet to be ONE legitimate ERROR named in this string

I thought I had a couple of legit errors (yes, many are just formatting/presentation) in post #2, no? But, again, I was using the e-mailed PDF practice exams. Maybe the published book addressed these few errors. I wouldn't worry about the comments here c_n. Everyone is under a lot of stress at this time, a day or two before the exam. After they pass, they'll forget all about any negative comments they might have had and will only have positive comments for this book.

 

[Jayman_PE]

There has yet to be ONE legitimate ERROR named in this string

Wrong. Try reading your own book Dr.

 

[Jayman_PE]

Hey Dr.,

Not one legitimate error? In addition to what's posted above, apparently the following aren't legitamate errors either

• Page 251, Problem 304. Solution gives angle of friction = 0, yet question gives friction angle = 15. I get ka=0.5, not 0.34.
  
• Page 17, Problem 31. Problem assumes bucket capacity @ loose measure. Only the truck would have loose measure, not bucket. Thus, no. of days = 9.
  
• Page 322, Problem 616. Total cost is wrong, because truck operational cost is wrong, because total truck hours are wrong. I'll leave it to you to explain why this is not a legimitate error.
  

Thanks,

Jason

 

[Jayman_PE]

None of this is meant to wage a personal attack of any kind toward the author. The last I checked there is no law against composing a subpar book. It's just frustrating when we are all trying so hard to study, and pay a lot money for these books. This book is not unique. Korman's Construction Depth and Huang's 6 minute construction solutions are worse than this one. Huang has at least 12% of the problems wrong in her book, and I am sure I missed one or two along the way. I am not counting grammar errors - who cares. I can overlook a few issues here and there, but these are major errors that suggest minimal proofing prior to publication.

Again, nothing personal against anyone here. I'm sure the Dr. is a great person. But when you charge good money you should produce a good product.

thanks,

Jason

 

[civilized_naah]

I am going to respond even though I am pretty sick of the tone that this conversation has taken. This is just so, whatever is within my powers to clarify, I will clarify, ahead of the upcoming exam. The ONLY ones that merit a response (IMHO) are shown below:

Problem 31. Problem assumes bucket capacity @ loose measure. Only the truck would have loose measure, not bucket. Thus, no. of days = 9.

RESPONSE:

So when soil is dug up and released from confining pressures, there is no bulking?

Problem 140. Not clear what we are asked to find: net cost of what? Crashing Schedule option vs. Normal Schedule?

RESPONSE:

Agreed. The language could definitely have been clearer. As solved, the word ‘net’ implies cost - bonus + penalties for crashing.

Problem 304. Solution gives angle of friction = 0, yet question gives friction angle = 15. I get Ka=0.5, not 0.34.

RESPONSE:

Angle of friction between BACKFILL soil and wall stem is taken to be zero. It is not specified and does NOT have to be the same as the angle of friction between the NATIVE soil and the wall footing, which is given as 20 (not 15). There does not seem to be any error in the value of Ka

Problem 315: Error in calculating depth from bottom 2/3 of pile length to middle of clay layer being compressed, …

RESPONSE:

THANK YOU FOR THIS CORRECTION

The thickness that will consolidate is 23.33 ft thick, with center 11.67 ft below point of load transfer. The corrections are:

Delta p = 342.6

P2 = 4697.6

Settlement = 2.6 in

Problem 337- error- shouldn't square y1 and y2 terms in solution,

RESPONSE:

WHY NOT?

Problem 339- Shouldn't use Ca for group pile skin friction (just use cohesion, no alpha reduction like with single pile).

RESPONSE:

THANK YOU FOR THIS CORRECTION

The diagram for problem 315 should have been used here. The cohesion should be used instead of adhesion.

Problem 616. Total cost is wrong, because truck operational cost is wrong, because total truck hours are wrong.

RESPONSE:

THANK YOU FOR THIS CORRECTION

Total truck operating hours = 1134x2.583 = 2929 hrs (was multiplied by just 2 instead of 2.583)

Truck operating cost = 234,330

Total cost = 326,880

Cost per cu yd = 21.79

 

[terzaghi83]

Problem 337- error- shouldn't square y1 and y2 terms in solution,

RESPONSE:

WHY NOT?

According to Both VNS Murhthy and Braja Das texts, these values are not squared for a confined aquifer. They are however, squared in the equation for an unconfined aquifer.

Additional error: in problem 318 solution: resultant earth pressure is listed as 35,513- think it should be 41,313. I think this may just be a math error in the solution and the procedure is correct.

Also- problem 307, shouldn't the solution subtract out the depth of material removed for the mat construction when calculation delta P for settlement equation?

I still think there is an error in the solution to 304. Solution states that rankine's active earth pressure coefficient is Ka is .339. If you use rankine's equation modified for the sloping back fill you get Ka =.311, unless I'm mistaken

Thanks for taking the time to respond. Sorry for negative tone but it is frustrating finding errors in solutions when trying to prepare for an exam, I think I have found a total of 6 errors out of 40 problems (with 1 of them maybe being a simple math error). While trying to learn, you may think you have been doing it wrong all along and the solution is correct, or even worse learning something wrong for the first time (like me trying to compute settlement of the pile group). I spent some time comparing some of the errors to other sample problems and solutions to figure out what was correct and incorrect.

My apologies and Thanks again.

 

[terzaghi83]

additionally,

I never did understand why in the solution to problem 335 the CSR*effective overburden stress goes in the denominator of the of the FS of equation, yet it goes into the numerator in the 2007 NCEES and 2011 NCEES sample exam. I don't know much about this topic but one must be incorrect.

 

[civilized_naah]

additionally,

I never did understand why in the solution to problem 335 the CSR*effective overburden stress goes in the denominator of the of the FS of equation, yet it goes into the numerator in the 2007 NCEES and 2011 NCEES sample exam. I don't know much about this topic but one must be incorrect.

I believe in the NCEES question (no. 514 from the 2010 version), the questions states: "maximum allowable cyclic stress ration is 0.29". To me that reads like the cyclic STRENGTH ratio is 0.29. That's why in their solution, they calculate the ULTIMATE shear stress based on this and put it in the numerator of the FS calc. There's nothing wrong with that, except it should not be called the cyclic stress ratio (but they did put the words "maximum allowable" in front of it, so it is kind of OK).

In problem 335, the question states "cyclic stress ration for s design earthquake is 0.21". That means that the actual cyclic shear stress due to this earthquake is to be calculated using the 0.21 value. That's why it belongs in the denominator.

Both are correct.

 

[civilized_naah]

Problem 337- error- shouldn't square y1 and y2 terms in solution,

According to Both VNS Murhthy and Braja Das texts, these values are not squared for a confined aquifer. They are however, squared in the equation for an unconfined aquifer.

Are you sure, you are not using the version that uses the drawdown values s1 and s2, instead of the water elevation values y1 and y2?

 

[civilized_naah]

I still think there is an error in the solution to 304. Solution states that rankine's active earth pressure coefficient is Ka is .339. If you use rankine's equation modified for the sloping back fill you get Ka =.311, unless I'm mistaken

I have checked this again with a spreadsheet. Linear interpolation from Table 208.1 in the All in One book had yielded Ka = 0.,339, but the exact value I am getting is Ka = 0.334. I am not getting the 0.311 you mentioned. I will check that spreadsheet again, or do it over

 

[Jayman_PE]

I am going to respond even though I am pretty sick of the tone that this conversation has taken. This is just so, whatever is within my powers to clarify, I will clarify, ahead of the upcoming exam. The ONLY ones that merit a response (IMHO) are shown below:

Problem 31. Problem assumes bucket capacity @ loose measure. Only the truck would have loose measure, not bucket. Thus, no. of days = 9.

RESPONSE:

So when soil is dug up and released from confining pressures, there is no bulking?

Of course there is release in a bucket volume but not as much as in a truck. When reading the problem that's what I thought was the intent, so I disregarded the swell - thinking it was intended for hauling. So what you are saying is the swell in the bucket is 20%. OK. I would add 2 words to clarify

The bucket material has the following properties.

Thanks for coming on here and facing the music. Again, no offense intended. Just trying to clarify.

All the best,

Jason

 

[terzaghi83]

Thanks for the clarification on the seismic issue.

Regarding problem 304: solution states Rankines active earth pressure coefficient is .339. Using the equation in VNS Murhty text for rankines active earth pressure I get .311. Same equation is in both braja das fundamentals of geotech 3rd ed. and pricnciples of foundation engineering 5th ed, yielding same result. Additional, Braja das has a table in both of the referenced books that have values of Ka listed for rankine's condition with sloping backfill. Using slope=15 and phi=34, both tables show Ka=.311. I have confirmed it with equations and tables in two books (allthough it appears that the tables are the same) but I am not sure where the .334 comes from. It would be helpful if the solution showed the calculation to obtain Ka, or where it was obtained from rather than just listing it.

"Are you sure, you are not using the version that uses the drawdown values s1 and s2, instead of the water elevation values y1 and y2?"

I was using the equation in the VNS Murthy text which uses the values y1 and y2 which are measured from the aquifer bottom, and the terms are not squared. I went back and solved it with two different equations- one using the drawdown distances with log in the equation, and another with drawdown distances with natural log in the equation. Not in any of the 3 different confined aquifer equations are the distance terms squared regardless of whether you are measuring height or depth of drawdown. Conceptually, it does not make sense as to why this difference would require squaring in one form but not the other. I get a drawdown of 0.83 feet using all 3 methods, and I think you are incorrect in squaring the distance terms for a confined aquifer regardless of whether measuring drawdown depth or height.

You didn't respond to my question about problem 307, which i think also has an error. Shouldn't the solution subtract out the depth of material removed for the mat construction when calculation delta P for settlement equation? I think goes along the lines of a "fully compensated foundation" where lowering the foundation helps reduce the increase in pressure the soil below is seeing.

Thanks again.

 

[terzaghi83]

And just to follow up, it truly is helpful that you are taking the time to respond to what may may or may not be errors to help us on the exam tomorrow!

I'm ready for this thing to be over with. Good luck to everyone...

 

[civilized_naah]

Regarding problem 304: solution states Rankines active earth pressure coefficient is .339. Using the equation in VNS Murhty text for rankines active earth pressure I get .311. Same equation is in both braja das fundamentals of geotech 3rd ed. and pricnciples of foundation engineering 5th ed, yielding same result. Additional, Braja das has a table in both of the referenced books that have values of Ka listed for rankine's condition with sloping backfill. Using slope=15 and phi=34, both tables show Ka=.311. I have confirmed it with equations and tables in two books (allthough it appears that the tables are the same) but I am not sure where the .334 comes from. It would be helpful if the solution showed the calculation to obtain Ka, or where it was obtained from rather than just listing it.

"Are you sure, you are not using the version that uses the drawdown values s1 and s2, instead of the water elevation values y1 and y2?"

I was using the equation in the VNS Murthy text which uses the values y1 and y2 which are measured from the aquifer bottom, and the terms are not squared. I went back and solved it with two different equations- one using the drawdown distances with log in the equation, and another with drawdown distances with natural log in the equation. Not in any of the 3 different confined aquifer equations are the distance terms squared regardless of whether you are measuring height or depth of drawdown. Conceptually, it does not make sense as to why this difference would require squaring in one form but not the other. I get a drawdown of 0.83 feet using all 3 methods, and I think you are incorrect in squaring the distance terms for a confined aquifer regardless of whether measuring drawdown depth or height.

You didn't respond to my question about problem 307, which i think also has an error. Shouldn't the solution subtract out the depth of material removed for the mat construction when calculation delta P for settlement equation? I think goes along the lines of a "fully compensated foundation" where lowering the foundation helps reduce the increase in pressure the soil below is seeing.

Thanks again.

Q 304: I have double checked the spreadsheet and verified the results in there against Table in the All In One book. I have verified multiple values obtained from the spreadsheet versus independent sources. The .334 was obtained by interpolation from the table for Rankine E.P. in the All In One book.

On the aquifer question, if the y is not squared, that equation (All In One eqn 205.23) would not be unit-consistent. Q has units of L^3/T. Right hand side of the equation is L^3/T. If you change the y^2 terms to y, the right side has units L^2/T

Q. 307. You are correct, I forgot to write that one in. The soil removed for the mat corresponds to to a pressure of 399 psf, which should be a reduction of p2

 

[terzaghi83]

Thanks once again.

 

[terzaghi83]

After re-looking at things I'm convinced that there must be an error in your table for Rankine's Ka with sloping backfill in all in one book.

Also, while the units are working out in your equation for confined aquifer, I'm still convinced it is incorrect. The confined aquifer equation should have a term in there somewhere for the thickness of the confined aquifer, which will then make the units work out when you don't square the distance terms. See eq. 21.27 in CERM 12 ed, or the Murthy text or braja texts referenced above which all include a term for the thickness fo the aquifer and do not square the distances..

I'm holding to it that there are at least 6 to 7 errors out of the 40 geotech problems, with 1-2 of them being simple math errors and the others being procedural or equation errors that could easily lead someone down the wrong path for the exam.

Many thanks for the responses, I'm traveling to my testing location soon- ready to have this one behind me!

 

[civilized_naah]

Thanks for the clarification on the seismic issue.

Regarding problem 304: solution states Rankines active earth pressure coefficient is .339. Using the equation in VNS Murhty text for rankines active earth pressure I get .311. Same equation is in both braja das fundamentals of geotech 3rd ed. and pricnciples of foundation engineering 5th ed, yielding same result. Additional, Braja das has a table in both of the referenced books that have values of Ka listed for rankine's condition with sloping backfill. Using slope=15 and phi=34, both tables show Ka=.311. I have confirmed it with equations and tables in two books (allthough it appears that the tables are the same) but I am not sure where the .334 comes from. It would be helpful if the solution showed the calculation to obtain Ka, or where it was obtained from rather than just listing it.

This was bugging me, so I checked Das' Principles of Geotechnical Engineering. Table 10.3 in that book presents Ka values for various combinations of the angles. However, that table assumes delta = 2/3 phi. On the other hand, in the problem 304, delta = 0. I have checked the table in the All In One book and it matches the data in Das' table in every way - it just does not make the assumption that delta = 2/3 phi. When I input the condition delta = 2/3 phi into my spreadsheet, the numbers are identical to Das' numbers. So, you can have confidence in the table in the All in One, because it is based on that same spreadsheet.

If you use delta = 0 into the equations, the Ka coeff should be 0.334 (which I got to be 0.339 by interpolation from the All in One table.

 

[civilized_naah]

Also, while the units are working out in your equation for confined aquifer, I'm still convinced it is incorrect. The confined aquifer equation should have a term in there somewhere for the thickness of the confined aquifer, which will then make the units work out when you don't square the distance terms. See eq. 21.27 in CERM 12 ed, or the Murthy text or braja texts referenced above which all include a term for the thickness fo the aquifer and do not square the distances..

No, the exact theory for both unconfined AND confined aquifers is exactly the same - the difference is that for the unconfined one, y refers to the elevation of the water table (measured from the aquifer bottom) while for the confined one, y refers to the elevation of the piezometric surface (measured from the aquifer bottom). And both of those equations are CERM equation 21.25, in which y is squared. On the other hand, if the aquifer (either type) is very deep (Y >> s), then this can be replaced by the (approximate) equation that includes Y and is written in terms of the drawdown s (linear not squared). This latter approximate equation is 21.26.

Thus, there is no mistake in the solution since it uses the WT elevation.

 

[terzaghi83]

I will look into the confined aquifer theory as I am assuming you are correct. I am just hoping that it will not be on the exam at this point!

Regarding the earth pressure coefficients: The table I am referring to is table 7.1 in the 5th edition of the foundation book, which is for RANKINE earth pressure (no delta and vertical back wall). The table you referenced is for Coulomb earth pressure coefficients, and assume delta is 2/3 phi as you described (and there is another for delta=1/2 phi.)

The solution states that the RANKINE earth presure coefficient is .33whatever when in fact it is .311. My understanding is that in general, a good rule of thumb is to use rankine's theory for cantilever walls and coulombs theory for gravity walls.

As stated, I appreciate the help.

 

[Jayman_PE]

Regarding the All-in-One book, I did not have time to post the errata that I found (I bought the book new October 2011), but might also want to check the Nc, Ny, Nq values in the Terzaghi bearing capacity table. I am traveling today and do not have the book with me, but I recall some values being inconsistent with the same shown in Das and CERM 12 Ed.

thanks,

Jason