huangyhg

retaining wall queries
hello all. i recently found this message board and was quite excited. i have just joined and am posting my first query of many i am sure. i feel obliged to provide a little back ground on myself - i live in canada [limit states design] and i have been working as a project manager and estimator for some time now. i have been supervised recently, outside of my main workplace, by a structural engineer [who i feel guilty about bombarding with questions] as a requirement to acheive one year of supervised design as a requirement of our provincial engineering association [apegga] prior to my ability to receive professional engineering status. i have always been extremely interested in structural engineering as that was one of my areas of specialization in my civil engineering degree program. i want to work in design/build someday but for now i just need to work hard and get design experience.
blah blah - now for the question:
please see the attachment as it outlines my queries. question number 5 is my main interest however all feedback is appreciated...
i hope some of you out there will find the time to provide any direction.
also - if there are any books [lsd in metric] that can be recommended for any areas of design i would love to know about them.
thank you, jim
1.) if the wall is restrained, use the at-rest pressure (use ko), but if the wall is a cantilever wall as you show above then use the active pressure (use ka). the 0.5 is typically used for an at-rest pressure coefficient with something on the order of 1/3 for active.
4.) i think it is appropriate to check the two cases you mention. they will envelope your design. that can get tricky, though, if you have an eccentric axial load on your wall.
5.) i really need to reply to this when i have some more time to sit and look through your attachment a little further. i don't have that time right now.
1. a geotechnical report will give two values, a ka value when the top of the wall is allowed to displace laterally and a larger ko factor when such displacement cannot occur. i have found for fill material a ka value of 0.4 is reasonable.
2. for what you have shown on your sketch, i would also assume some hydrostatic pressure behind the wall, this will have a significant impact. in australia, where the water table is deep below surface level, i assume water behind one-third of the wall.
4. check both cases, the lateral forces will cause sliding and overturning which is largly resisted by vertical loads for a cantilever retaining wall, i ignore passive earth pressure in front of the wall because the soil may shrink away from the wall due to moisture content, there may be en excavation in the future etc.
maximum vertical forces should also be considered to ensure bearing capacity under the wall is not exceeded.
5. the sketch looks good, their was a post recently about the distribution of moment from the wall to the toe and heel respectively.
it's good that project managers are keen on design because most of them have engineering degrees. remember the engineer will be very busy and is unlikely that they want to answer your questions. if your going to do something, ensure that you have a good source to back you up.

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