coupled soil-pile axial interaction with consolidating soil

[JoseLeo]

at the moment I am performing uncoupled analysis of axial soil-pile interaction to study negative skin-friction (NSF) under the effects of a consolidating soil due to surcharge load using 1D soil-pile model with Tz-Qz springs, by: (1) performing a separate finite difference analysis of consolidation, (2) determining the ultimate properties of the nonlinear T-z springs by effective stress (beta) method at any time when NSF is to be evaluated, (3) imposing the consolidation settlements in the soil layers as downward vertical displacements on the free-ends of the T-z springs, and (4)performing a nonlinear load transfer analysis. I got reasonable results that matched well with case studies of several pile tests.

now I want to make a coupled analysis by attaching my 1D soil-pile model with PressureDependent nDMaterials and UCDavis Soil Elements, and a T-z spring interface element. My problem is that I am stucked with step (2) above. Since I use the effective stress method, how can I change the ultimate properties of my nonlinear T-z springs at every time step during consolidation process?

Is my coupled model feasible or correct? or Has anyone performed coupled axial soil-pile interaction under a consolidating soil subjected to surcharge loads at its surface.? I really appreciate your comments and suggestions.

thank you.

[kavya1811]

Dear Jose,

I am happy to see your post on axial load transfer of pile in soils. I am just in the learning stage. I am not able to simulate simple pile load test to get the force and vertical displacements on saturated soil mass.

Do you have any example of simple model to share with? I will be really happy.

I modelled soil, pile and tied their contact nodes with equalDOF. But whatever the load I applied on the pile head is not transferring to the soil as a shear stress and end bearing stress at the bottom. It is just transforming the vertical load as point load through out the pile section.

I am really in a need of your help. Can you please help me?

Thanks in advance!

Here is my input file.. for your kind reference to help me.

wipe
model BasicBuilder -ndm 2 -ndf 2
node 1 10.000 0.000
node 2 5.000 0.000
node 3 10.000 5.000
node 4 5.000 5.000
node 7 0.000 0.000
node 8 10.000 10.000
node 11 0.000 5.000
node 12 5.000 10.000
node 14 0.000 10.000

nDMaterial ElasticIsotropic 1 20900 0.3

element quad 1 11 4 12 14 1 PlaneStrain 1 0 0 20
element quad 2 7 2 4 11 1 PlaneStrain 1 0 0 20
element quad 3 1 3 4 2 1 PlaneStrain 1 0 0 20
element quad 4 3 8 12 4 1 PlaneStrain 1 0 0 20

fix 1 1 1
fix 2 1 1
fix 3 1 1
fix 7 1 1
fix 8 1 1
fix 11 1 1
fix 14 1 1

system ProfileSPD
constraints Transformation
test NormDispIncr 1e-12 25 0
integrator LoadControl 1 1 1 1
algorithm Newton
numberer RCM
analysis Static

analyze 1
#####################################################################

setTime 0.0
loadConst
wipeAnalysis

#####################################################################

model BasicBuilder -ndm 2 -ndf 3
geomTransf Corotational 1
node 5 5.000 5.000
node 6 5.000 5.000
node 9 5.000 10.000
node 10 5.000 10.000
node 13 5.000 11.000 -mass 0.000 10.000 0.000

puts "read pile nodes"

uniaxialMaterial Steel02 2 290000000 7.00E+010 0.003 20 0.925 0.15

puts "read pile material"


#creat section Fiber
section Fiber 1 {

# Create the pile fibers
patch circ 2 20 4 0 0 0.0001 0.5 0 360
}

puts "read pile section"

# pile elements
#element dispBeamColumn $eleTag $iNode $jNode $numIntgrPts $secTag $transfTag <-mass $massDens>
element dispBeamColumn 7 13 10 10 1 1 -mass 3700
element dispBeamColumn 8 10 5 10 1 1 -mass 3700

puts "read pile elements"

uniaxialMaterial TzSimple1 3 2 10 0.002 120
uniaxialMaterial QzSimple1 4 2 100 0.008 0.0 230

puts "read tz,qz materials"

#zero length Elements for soil
#element zeroLength $eleTag $iNode $jNode -mat $matTag1 $matTag2 -dir $dir1 $dir2
element zeroLength 5 5 6 -mat 2 4 -dir 1 2
element zeroLength 6 10 9 -mat 2 3 -dir 1 2

puts "read zerolength elements"

equalDOF 4 5 1 2
equalDOF 12 10 1 2

puts "read nodes tie up"

##################################################################
wipeAnalysis
setTime 0.0
loadConst

pattern Plain 1 "Linear" {
load 13 0 -50 0 0 0 0
}

print node 13
eigen 3
print NodeProp.txt -node
puts "T1 = [expr 2*3.1416/(pow([eigen 1] ,0.5))] sec"

recorder Node -file dis.out -time -nodeRange 1 14 -dof 1 2 disp

test EnergyIncr 1.0e-8 30 0
algorithm Newton
system BandGeneral
numberer RCM
constraints Plain

integrator DisplacementControl 1 1 0.001

analysis Static

analyze 10
##################################################################