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Jean-Louis BRIAUD – Texas A&M University
DESIGNING FOR DOWNDRAG ON UNCOATED AND
BITUMEN COATED PILES
Jean-Louis BRIAUD, PhD, PE
President of ISSMGE
Professor and Holder of the Buchanan Chair
Texas A&M University
Piling and Deep Foundations Middle East 2010
1 February 2010
Jean-Louis BRIAUD – Texas A&M University
1. What is downdrag?
2. Predicting pile behavior subjected to downdrag
3. Design and selection of bitumen
4. Example problem
5. Full scale field test in New Orleans, LA, USA
6. Full scale field test in Edmonton, AL, Canada
7. Conclusions
Content Outline
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
What is downdrag?
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
When to Design for Downdrag
Jean-Louis BRIAUD – Texas A&M University
Design to Avoid these Three Conditions
Jean-Louis BRIAUD – Texas A&M University
Static Equilibrium
max t n p pQ Q F F Q
Jean-Louis BRIAUD – Texas A&M University
Finding the Depth of Neutral Point
ωpile(NP) = ωsoil(NP)
ωsoil(NP)= read on
consolidation
settlement profile (given)
ωpile(NP) = ωpoint + ωelastic
ωpoint = ω soil (@Z=L) +ωpunch
ωelastic = elastic compression
from bottom to NP
Jean-Louis BRIAUD – Texas A&M University
Pile Point Behavior
2(1 )4
p
punch
s
Q Dv
AE
ωpunch = Pile point movement
ν = Poisson’s ratio
Qp = Point resistance
A = Area of pile point
D = Diameter of pile point
Es = Soil modulus
For clays
Es = 100 Su = Epmt
For sands
Es (kPa) = 800 N = 2 Epmt
Jean-Louis BRIAUD – Texas A&M University
Pile Point Behavior
1
2elastic p p
L ZQ F
AE
ωelastic = Elastic compression
of pile
Qp = Point resistance
Fp = Positive friction force
L = Depth of pile point
Z = Location of NP
A = Area of pile point
E = Pile modulus
Jean-Louis BRIAUD – Texas A&M University
FOR PILES IN CLAY (short term and long term)
fmax = Su fmax = σ’ov
Maximum Friction
Jean-Louis BRIAUD – Texas A&M University
FOR PILES IN SAND fmax = σ’ov
fmax (kPa) = 5 (N)0.7
N = SPT blow count
Maximum Friction
Jean-Louis BRIAUD – Texas A&M University
FOR PILES IN SANDS AND IN CLAYS
Clay (short term) qmax = 9 Su
Clay (long term) qmax = σ’ov Nq
Sand (short & long term) qmax (kPa) = 1000 (N)0.5
Sand (short & long term) qmax = σ’ov Nq
Maximum Point Resistance
2 max
max (1 )4 s
q Dv
AE
Jean-Louis BRIAUD – Texas A&M University
Downdrag on Pile Groups
Jean-Louis BRIAUD – Texas A&M UniversityAfter Okabe, 1977
Downdrag on Pile Groups
Jean-Louis BRIAUD – Texas A&M University
Reduction
Factors for
Downdrag in Pile
Groups
Jean-Louis BRIAUD – Texas A&M University
- Developed at Texas A&M University
- Analyzes axially-loaded single piles under both
positive and negative skin friction
- Bitumen coated piles can also be analyzed with
the program
PILENEG
http://ceprofs.tamu.edu/briaud/pileneg/pileneg.zip
Jean-Louis BRIAUD – Texas A&M University
PILENEG Inputs
- Top load on pile
- Pile data (cross section area of the pile, pile
perimeter, embedded pile length, pile modulus)
- Soil data (profile of maximum friction, soil
settlement profile, soil modulus and Poisson’s
ratio at point, ultimate bearing pressure at point)
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
- Top load, top settlement, depth of bitumen
coating, depth to neutral point, maximum load,
maximum stress and pile point load
PILENEG Outputs
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
WHAT IS BITUMEN?
A black viscous substance. The residue left at the
end of the refining process of crude oil, made of
high molecular weight hydrocarbons
WHAT IS A PRIMER?
A liquid made of half bitumen and half solvent to
liquefy the bitumen for easy application and filling
the holes. The layer left is largely the bitumen
after drying.
Jean-Louis BRIAUD – Texas A&M University
Bitumen is a viscous material τ = η (dγ/dt)
Behavior of Bitumen
Jean-Louis BRIAUD – Texas A&M University
τ = η (dγ/dt)
Jean-Louis BRIAUD – Texas A&M University
τ = η (dγ/dt)
η decreases when dγ/dt increases
dγ/dt x 10 leads to ~ η / 2
η decreases when T increases
T x 2 leads to ~ η / 10
η much more sensitive to T than dγ/dt
Jean-Louis BRIAUD – Texas A&M University
τ = η (dγ/dt)
• Storing
• Driving
• Downdrag
• Particle penetration
SOIL
Bitumen Selection
Jean-Louis BRIAUD – Texas A&M University
Storage Criterion
2
( )req storage
gtd
h
ρ = Bitumen mass density
g = Acceleration due to
gravity
t = Max anticipated storage
period
d = Bitumen coating
thickness
h = Allowable bitumen flow
distance (usually taken as
equal to d)
Storage requires:
η > ηreq(storage)
Jean-Louis BRIAUD – Texas A&M University
Driving Criterion
2
( , )
a a
req driving air
a
v d
h
ρ = Bitumen mass density
va = Velocity of bitumen in
the air (taken as the velocity
of the hammer at time of
impact)
d = Bitumen coating thickness
h = Allowable bitumen flow
distance (usually taken as
equal to d)
fmax = Maximum friction
t = Max anticipated storage
period
Driving in air requires:
η > ηreq(driving, air)
max
( , )
s
req driving soil
f td
h
Driving in soil requires:
η > ηreq(driving, soil)
Jean-Louis BRIAUD – Texas A&M University
Downdrag Criterion
( )
2 1
2 1
bit bit bit
req downdrag
s
d d
s s s
t t
τbit = Allowable shear stress
on bitumen (τbit ~ 0.1 τs,avg)
τs,avg = Soil shear strength
d = Bitumen coating thickness
s = Settlement rate
s1 , s2 = Settlements of the
ground surface at times t1
and t2, respectively (after
placement of an embankment
or other load)
Downdrag requires:
η < ηreq(driving)
Jean-Louis BRIAUD – Texas A&M University
Particle Penetration Criterion
' '
H OVK
FOR DRIVEN PILES: K = 1
FOR BORED PILES: K = K0 = (1-sinΦ)OCR0.5
Jean-Louis BRIAUD – Texas A&M University
Bitumen Design Criteria Summary
Jean-Louis BRIAUD – Texas A&M University
EXAMPLE:
Find allowable top load for
a top settlement < 14 mm
1) Pile Ult. Capacity
Qu = (25x1.2x30) + 1000
Qu = 900 + 1000 = 1900 kN
Jean-Louis BRIAUD – Texas A&M University
EXAMPLE:2) Assume a top load = 500 kN
and find the maximum depth to
NP
500 + X = 1000 + (900 - X)
X = 700 kN or 23.3 m of friction
ωNP(soil) = 35 mm (settlement profile)
ωtop = 35+(850*23300)/(0.09*2E7) = 46 mm
(This is more than the allowable settlement)
Jean-Louis BRIAUD – Texas A&M University
EXAMPLE:3) Assume a top load = 100 kN
and NP = 29 m
Qp = 100 + 870 - 30 = 940 kN
ωp = 4.7 mm
ωNP(pile) = 4.7 + (955*1000)/(0.09*2E7)
= 5.2 mm ~ ωNP(soil)
ωtop = 5 + (535*29000)/(0.09*2E7)
= 13.6 mm
Jean-Louis BRIAUD – Texas A&M University
EXAMPLE:4) Use bitumen coating with shear
strength = 2.5 kN/m2 and try a top
load of 500 kN (Assume NP = 29 m)
ωNP(soil) = 5 mm
Qp = 500 + 87 – 30 = 557 kN
ωp = 2.8 mm
ωtop = 5 + (543.5*29)/(0.09*2E7)*(1000)
= 13.8 mm
Jean-Louis BRIAUD – Texas A&M University
ωtop = 46 mm ωtop = 14 mm ωtop = 14 mm
with bitumen
Jean-Louis BRIAUD – Texas A&M University
Full Scale Field
Test:
Alberta,
Edmonton, Canada
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
CONSTRUCTION AND
SPECIFICATIONS
• Clean surfaces (free of dust and grease)
• Apply the primer (wait 24 hrs for drying)
• Apply the bitumen (10 mm thick)
• Storing (cold, hot)
• Handling in the field (pad eye, no strap)
• Drive the piles (splice, temperature)
Jean-Louis BRIAUD – Texas A&M University
• Clean surfaces (free of dust and grease)
• Apply the primer (wait 24 hrs for drying)
Jean-Louis BRIAUD – Texas A&M University
Applying the bitumen (10 mm thick)
Jean-Louis BRIAUD – Texas A&M University
Applying the bitumen (10 mm thick)
Jean-Louis BRIAUD – Texas A&M University
APPLYING BITUMEN
COATING OUTSIDE IN
THE COLD
BITUMEN BECOMES
BRITTLE DUE TO
COATING OUTDOORS
Jean-Louis BRIAUD – Texas A&M University
Handling in the field
Jean-Louis BRIAUD – Texas A&M University
Storing the coated piles
In hot weather, store under cover away
from direct sunlight
In cold weather, wait until bitumen
cools down before storing
Jean-Louis BRIAUD – Texas A&M University
Driving the piles (splice, temperature)
Jean-Louis BRIAUD – Texas A&M University
AVERAGE ANNUAL AIR TEMPERATURE = SOIL TEMPERATURE
Jean-Louis BRIAUD – Texas A&M University
1. Downdrag does not reduce the ultimate capacity
of a pile
2. Downdrag increases the load in the pile
3. Downdrag increases the settlement of a pile;
downdrag is a case where settlement controls the
pile design
4. Live loads should not be included in settlement
calculations including downdrag
General Observations
Jean-Louis BRIAUD – Texas A&M University
6. Downdrag makes a pile come out of the ground
7. Bitumen reduces downdrag significantly (90%?)
when properly chosen and properly applied
8. Bitumen is most easily applied when the air is
colder than the soil (winter) but when the
temperature is above freezing
9. Piles located on the inside of a pile group
experience less downdrag than the perimeter
piles
General Observations
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Videotape on Bitumen Coating
(email: [email protected])
Briaud J.-L., Tucker L.M., 1998, “Design
guidelines for downdrag on uncoated and
bitumen coated piles”, NCHRP Report 393,
National Academy of Sciences.
For more information
On Downdrag
https://ceprofs.tamu.edu/briaud/NCHRP_Downdrag.pdf
Jean-Louis BRIAUD – Texas A&M University
THANK YOU
http://ceprofs.civil.tamu.edu/briaud/
http://www.issmge.org/
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Full Scale Field Test:
New Orleans, Louisiana, USA
Jean-Louis BRIAUD – Texas A&M University
Full Scale Field
Test:
New Orleans,
Louisiana, USA
Jean-Louis BRIAUD – Texas A&M University
Full Scale Field
Test:
New Orleans,
Louisiana, USA
Jean-Louis BRIAUD – Texas A&M University
STEEL WOOD PPC
Jean-Louis BRIAUD – Texas A&M University
APPLYING PRIMER
COATING WITH BITUMEN
Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
Full Scale Field
Test:
Alberta,
Edmonton, Canada