# P&A Practice Exam 3 Case Study 2 Question 68

I am little confuse in scale system; metric or imperial for this case study. The guideline given in metric dimension first and assume the primary scale system use in this study is metric system, including the contour lines. One of the topographic map legend clearly says contour lines 1.0 m, so I assume the contour height is in metric. The guideline states any retaining walls in excess of 1.2 m in height required to have a structural design by a structural engineer. The driveway and lower level retaining walls will be more than 2 m, make the project will require a structural engineer to design all retaining walls could be reasonable answer. Would someone clarify the answer contain a word “all” makes this not reasonable/better answer? The answer description only says that project will require a structural engineer to design retaining walls only over 4 feet in height. Also three-level elevator location is not clear. The elevator could be placed at parameter or edge of the building instead of middle of building. Depending on the assumption, the elevator might require retaining wall too.

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Hi @smoriny so sorry for the delay on this response! @coachdarionziegler will be able to help with y9our P&A question!

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Hi @smoriny ,

The options says “Project will require a structural engineer to design all retaining walls.”
This answer is incorrect because only retaining walls over 1.2 meters (or 4’, as stated in the prompt) will require design by a structural engineer. All was the operative word in this option that made it incorrect.

The elevator is indoors. It will not have retaining walls associated with it even if it is located on the edge of the building – retaining walls support only soil. The elevator will likely have deeper foundations associated with its shaft than the rest of the building to allow for the pit and other depth requirements.

Hope this helps!
-Darion

Ms. Ziegler:

Thank you for your response. I am still a little confused. Assuming the grade level is 100 for the structure/building, the back wall will back up against elevation 104 means 4 meter (13 feet) elevation difference. I assume many of the retaining walls will end up more than 1.2 meter (4 feet).

Hi @smoriny ,

Let’s see if I can help clear this up.

There will be retaining walls built taller than 1.2 meters (4’), but not all of them will need to be that tall.

If the options was, “Project will require a structural engineer to design SOME retaining walls” it would have been correct.

However, the option was, “Project will require a structural engineer to design ALL retaining walls”, which is incorrect because not all of the retaining walls will be over 1.2m (4’).

It’s a tricky questions because it’s using that one word, “ALL”, to invalidate the option.

Please let me know if there is anything else I can do to help!

-Darion

Thank you. This question is very tricky for me. First the geological survey map is in metric even I assume the project is in the U.S. since international project will use designing in the metric system, and also the exam will not consider the project outside the U.S. jurisdiction. The building envelop is indicated in one rectangle shape in the site plan but will be the retaining wall/s will not be one continuous piece and to consider the “ALL” other retaining walls some at access roads, etc. which will be shorter than 1.2 meter tall. The map in the question 68 is no indication of scale, so I assume the scale is in imperial and find out/confirm the scale in later map on question 71 which indicate the map provided is in metric. If anyone take break between the question, will not be able to go back and check your answer. Hope the actual exam is not in mixed scale and not as tricky as this practice exam.