Earth Pressure Distribution Models for Flexible Wall Systems
Earth Pressure Distribution Models for Flexible Wall Systems
(OP)
Hi,
This is my 1st post and I'm new to this, therefore I hope it makes sense and I can get some great feedback from you guys...............
I would like to hear some expert opinion about the way in which earth pressures should be modelled when it comes to internally-braced and cantilever flexible sheet piled wall systems.
I have been designing multi-braced sheet piled cofferdams for a number of years now (for various in-house design teams) and I have heard various peoples takes on whether Triangular (eg. Rankine) OR Apparent Earth Pressures models (eg. T & P) should be adopted. Researching around on the web and using educational databases on this topic I have found there to be probably hundreds of documents and guidance documents from various states, countries, government establishments, CIRIA's, piling handbooks etc. all giving design examples and guidance in one way or another which contradicts somebody / somewhere else.
I am from the UK and the Rankine method is used extensively in almost every situation. Most temporary cofferdams are cantilever sheet pile jobs or are internally strutted jobs that are built in a staged dig down then prop sequence using simplified load sharing support analysis methods.
My own thoughts on this subject are that the Rankine analysis was done around 1860 (Coulomb 80 years even earlier) and considered only an active pressure acting on a solid non-flexible retaining systems and materials (such as masonry retaining walls) which was around at that time. I believe (from courses lectures), that Rankine underestimates the passive pressure by as much as 100% when compared to modern methods. Hardly suitable for a cantilever support! Therefore this method seams to not really be suitable for flexible; cantilever, single-propped or multi-propped embedded retaining walls which yield in different places depending where struts are located (if any) and require a passive toe-in? On the other hand T & P measured strut loads in various ground condition within different support types and came up with pressure envelopes. So this was for propped walls, therefore not really suitable for cantilever walls.
Can someone help with explaining something I might be missing or not understanding as it seams non of these methods are really appropriate in every circumstance.
I am interested to hear comments for these classic analysis methods and not going down the route of complex finite element analysis (unless they help explain my woes).
Thanks in anticipation
John





RE: Earth Pressure Distribution Models for Flexible Wall Systems
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RE: Earth Pressure Distribution Models for Flexible Wall Systems
Cofferdams where I work are almost entirely below the water table. Water pressure is the major component of the design pressure... typically over 2/3 of the total. The remainder is the equivalent liquid pressure (ELP) based on the submerged weigh of soil - usually an ELP less than 30 PSF. Any error in design pressure is confined the small submerged soil component. Water pressure, based on 62.4 PCF or 64 PCF for sea water, is accurately predictable. The actual water pressure and the calculated ELP for submerged soil are easily combined.
I'm assuming that typical retaining wall backfill is mostly above the water table. Therefore soil pressure has a much greater influence on design pressure. In that case, well worth the effort to predict soil pressure as accurately as possible.
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RE: Earth Pressure Distribution Models for Flexible Wall Systems
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RE: Earth Pressure Distribution Models for Flexible Wall Systems
RE: Earth Pressure Distribution Models for Flexible Wall Systems