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Gravity retaining wall with back slope and cohesive soil

  1. May 7, 2012 #1
    1. The problem statement, all variables and given/known data

    I have a gravity retaining wall with a backslope and an inlcined prestressed anchor. The soil properties are c'=5 kPa, phi`=15 degrees, gamma=16 kN/m3. The water table is well below the bottom of the retaining wall. I have been told to assume the wall adhesion is 80% of c'. There is no mention of taking into account wall friction.

    The solution asks for an anchor prestressing force and omptimal angle based on a safety factor of 2. This is simple provided I can work out all the forces acting on the structure.

    2. Relevant equations

    That is what I need to know.

    3. The attempt at a solution

    I have two choices here. Rankine's and Coulomb's theories of lateral earth pressure. Looking through Braja. M. Das: Principles of Geotechnical Engineering 7ED he gives treatment to both of these cases. He doesn't seem to include anything in Rankine's theories for a sloping backface and c'-phi`soil. How does the sloping backface affect the application of this theory? How can this theory take into account wall cohesion? I believe Rankine's theories do not take into account wall friction whatsoever. I have also read that Rankine's can offer a conservative design by underestimating the passive pressure and overestimating the active pressure.

    His treatment of Coulomb's theories takes into account the sloping backface and presents a graphical solution to a cohesionless soil problem. Again I have a cohesive soil and I need to take into account wall cohesion and wall friction. I also need to take into acount the passive pressure applied to the wall by the soil in front of the toe. His treatment of Coulomb's passive pressure is based on the retained earth not the earth in front of the toe. Why would you even want to calculate the pasive pressure applied by the retained earth?

    Is there a good text that expands on these theories a summarises them based on the wall and soil properties you have? It seems every time I go to design a retaining wall I have to spend hours sifting through texts of varying quality and conflicting recommendations do find a decent analogy and I really don't have that kind of time.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
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