wall/foundation soil interaction coefficient
wall/foundation soil interaction coefficient
(OP)
I am reviewing a retaining wall design. In the calculations, two parameters caught my attention. They are called "Wall Soil Interaction Coefficient" and "Foundation Soil Interaction Coefficient". For both parameters, a value of 0.9 are asigned. To my knowledge, such coefficient is the tangent of DELTA, the friction angle between wall/foundation and soils, and the tangent of DElTA rangs normally between 50 to 75 percent of tangent of PHI, the internal friction angle of soil.
The soils used in the design are silty sands and sandy silts, the friction angles are around 28-30 degrees. I think the assigned coefficient of 0.9 is too high, however, the designers insist the value is appropriate and even get offended by my questioning.
Can anybody provide any opinion? Am I wrong? What value would be more appropriate? Thanks
The soils used in the design are silty sands and sandy silts, the friction angles are around 28-30 degrees. I think the assigned coefficient of 0.9 is too high, however, the designers insist the value is appropriate and even get offended by my questioning.
Can anybody provide any opinion? Am I wrong? What value would be more appropriate? Thanks





RE: wall/foundation soil interaction coefficient
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RE: wall/foundation soil interaction coefficient
Refer to Table 5.5.2B in the AASHTO Standard Specifications for Highway Bridges. They have a range of values for different types of soils and foundations. A max value of 0.7 may be used for concrete foundations on clean sound rock. I have never seen anyone use 0.9.
RE: wall/foundation soil interaction coefficient
RE: wall/foundation soil interaction coefficient
Perhaps the designer is getting confused by the use of PHI for both symbols. If they are using LRFD, then review section 10.6.3.3 with them.
RE: wall/foundation soil interaction coefficient
I checked the DM 7.2 after you said. Looks like AASHTO took the table from there. Its exactly the same one. Although the table id given in the ASD Analysis section, I think the values would be universal. Would'nt you agree?
RE: wall/foundation soil interaction coefficient
I agree with Panars and BigH as to the origin for vertical walls. I also agree that I have not seen the more experienced and knowledgeable engineers using values this high.
RE: wall/foundation soil interaction coefficient
If you mean the interaction between soil and reinforcement,
that coef of 0.9 really depends on the type of reinforcement and dimension of grid of reinforcement. It could be less than 0.9 , but (i think) not less than 0.5.
RE: wall/foundation soil interaction coefficient
If you did understand this already, then I sincerely apologize.