sheetpile design Kp reduction factors and mobilized phi
sheetpile design Kp reduction factors and mobilized phi
(OP)
can someone explain this to me?
for sheetpile design, Kp is calculated several ways but im looking at Caquot and Kerisel. in school i was taught to reduce the phi of the passive soil by using a mobilized phi' = arctan(tan(phi)/FS)
use the charts to get the Kp
and then use the reduction factors to get the final Kp.
this seems like double reduction... is there a reason for this or is that too conservative?
thanks
for sheetpile design, Kp is calculated several ways but im looking at Caquot and Kerisel. in school i was taught to reduce the phi of the passive soil by using a mobilized phi' = arctan(tan(phi)/FS)
use the charts to get the Kp
and then use the reduction factors to get the final Kp.
this seems like double reduction... is there a reason for this or is that too conservative?
thanks





RE: sheetpile design Kp reduction factors and mobilized phi
I am familiar with factoring tan phi, but don't often do this myself. For the earth pressures that I usually calculate, I usually use phi and then a safety factor on the overall structure (e.g., retaining wall).
f-d
¡papá gordo ain't no madre flaca!
RE: sheetpile design Kp reduction factors and mobilized phi
Anyway, to use the tables:
1. Compute your Beta (retained slope angle to horizontal) and divide by phi.
2. enter the table from the bottom at the apporpriate phi and travel up to the correct beta over phi line. Go left and write down the result. For 34 degrees and no slope(B=0) and phi = 34, The result is about 9.2
3. Compute delta over phi. Delta is the angle of friction of soil against the sheet. I typically use 17 degrees for quartz sand on steel. Thus if phi = 34 degrees, delta over phi = .5 and R=.746 for phi =30 and R=.674 for phi= 35, thus with linear interpretation for phi = 34, R= .69
4. Kp = the result in 2 times R. For phi = 34 degrees,
Kp = 9.2 x .69 = 6.3
5. I then divide that by a factor of safety, which I typically set to 1.5. Some people do not reduce the Kp by a safety factor, but then add 20-30% to the length of the toe. I prefer to out the safety factor on the Kp.
RE: sheetpile design Kp reduction factors and mobilized phi
RE: sheetpile design Kp reduction factors and mobilized phi
RE: sheetpile design Kp reduction factors and mobilized phi
Alternatively if you use a nonlinear elasto-plastic FEM model such as provided in Plaxis, the full phi value may be used in the model and any reduction in passive resistance is accounted for by the computed deflections. Note also the wall bending moments will be substantially lower since the wall flexibility is included in the analysis. I then factor the wall moment by 1.6 per IBC for section design.
RE: sheetpile design Kp reduction factors and mobilized phi
I have designed and built a few thousand sheeting walls. Almost never have I reduced the Kp unless the project specifications insist. It isn't necessary and is not economical. As I wrote in a previous forum discussion, I do not know any specialty contractors in the design/build anchored wall business who regularly use Plaxis or other FEA programs to design their walls. Using these types of programs is overkill for almost all projects. For anchored walls designed using the FHWA/AASHTO LRFD method, factored loads are used and the full Kp is used with a resistance factor = 1.0.
RE: sheetpile design Kp reduction factors and mobilized phi
RE: sheetpile design Kp reduction factors and mobilized phi
With computers today, tedious calculations are easy. Many engineers forget about, or never knew, the old ways of design which still work fine today. If a proven method gives a better, more economical answer, shouldn't engineers have an obligation to use that method?
RE: sheetpile design Kp reduction factors and mobilized phi