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FOUNDATION ENGINEERING: RECENT ADVANCES

Downdrag on Piles, Laterally Loaded Pile, Spread Footings on Sand, Large Mat on

Stiff Clay

The 32nd Martin KAPP Lecture

by

Jean-Louis BRIAUD, PhD, PE Professor and

Holder of the Buchanan Chair Zachry Dpt. of Civil Engineering

Texas A&M University

New York City, 14 December 2006

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Jean-Louis BRIAUD – Texas A&M University

FOUNDATION ENGINEERING: RECENT ADVANCES

Downdrag on Piles, Laterally Loaded Piles, Spread Footings on Sand, Large Mat on Stiff Clay

The 32nd Martin KAPP Lecture

byJean-Louis BRIAUD, PhD, PE

Professor and Holder of the Buchanan ChairTexas A&M University


•ASCE MET Section and Geo-Institute Local Chapter

•Geoff Meyerhof (too complicated!)

•Louis Briaud (so what!)

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS

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•Research Principles

•Downdrag on Piles

•Laterally Loaded Piles

•Spread Footings on Sand

•Large Mat on Stiff Clay


1. Literature Review2. Dimensional analysis3. Test matrix optimization4. Model scale tests, scaling laws5. Numerical simulations6. Method development7. Full scale field tests, verification8. Threshold of optimum of simplicity

RESEARCH PRINCIPLESRESEARCH PRINCIPLES

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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

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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


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WHEN TO DESIGN FOR DOWNDRAG?


DESIGN TO AVOID THESE THREE CONDITIONS

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MAXIMUM FRICTIONFOR PILES IN CLAY (short term and long term)

fmax = αSu fmax = βσ’ov


MAXIMUM FRICTION FOR PILES IN SANDfmax = βσ’ov

fmax (kPa) = 5 (N)0.7

N = SPT blow count

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MAXIMUM POINT RESISTANCEFOR 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


POINT DISPLACEMENT TO REACH THE MAXIMUM POINT RESISTANCEFOR PILES IN SANDS AND IN CLAYS

wmax = 0.785 (1-ν2) qmax D / Esoil

D = pile diameterE = soil modulusFor claysE = 100 Su = EpmtFor sandsE (kPa) = 800 N = 2 Epmt

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FINDING THE DEPTH OF THE NEUTRAL POINT

Vertical Equilibrium

Qt + Fn = Fp + Qp


FINDING THE DEPTH OF THE NEUTRAL POINT

Compatibility of Movement

wpile = wsoil

wsoil = read on consolidation settlement profile

wpile = wpoint + elastic compression

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FINDING THE PILE SETTLEMENT

Wpile at top = wpile at bottom + elastic compression


FINDING THE LOAD SETTLEMENT CURVE

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DOWNDRAG ON PILE GROUPS



After Okabe, 1977

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REDUCTION

FACTORS FOR

DOWNDRAG ON

PILE GROUPS


EXAMPLE

Pile Ult. Capacity

Qu = 706 + 1000

Qu = 1706 kN

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wtop = 46 mm wtop = 14 mm wtop = 14 mmwith bitumen


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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.


HOW DOES BITUMEN BEHAVE?

Bitumen is a viscous material τ = η (dγ/dt)

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τ = η (dγ/dt)


τ = η (dγ/dt)

η decreases when dγ/dt increasesdγ/dt x 10 leads to ~ η / 2

η decreases when T increasesT x 2 leads to ~ η / 10

η much more sensitive to T than dγ/dt

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HOW TO CHOSE A BITUMENT THAT WORKS?

τ = η (dγ/dt)

• Storing

• Driving

• Reducing downdrag

• Particle penetration

SOIL


HOW TO CHOSE A BITUMENT THAT WORKS?

τ = η (dγ/dt)

• Storing

• Driving

• Reducing downdrag

• Particle penetration

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AVERAGE ANNUAL AIR TEMPERATURE = SOIL TEMPERATURE


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)

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• Clean surfaces (free of dust and grease)• Apply the primer (wait 24 hrs for drying)


Applying the bitumen (10 mm thick)

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Applying the bitumen (10 mm thick)


Handling in the field

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Storing the coated piles

In hot weather, store under cover away from direct sunlight

In cold weather, wait until bitumen cools down before storing


Driving the piles (splice, temperature)

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PILNEG, free softwarehttp://ceprofs.tamu.edu/briaud/

Videotape on Bitumen Coating(email Briaud)

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 informationFor more informationOn On DowndragDowndrag







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LATERAL LOAD-DEFLECTION CURVE

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THE TEXAMPRESSUREMETER1981

SimpleSafeVersatile

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ULTIMATE HORIZONTAL LOAD, Hou

Hou = ¾ pl B Dv

pl = limit pressure from PMTB = projected pile widthDv = (π/4) lo with lo = (4EI / K)1/4 for L > 3 loDv = L/3 for L < loE = modulus of pile materialI = moment of inertia of pileK = 2.3 EoEo = PMT first load modulus of soilL = pile length


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SAND (36 sites)


CLAY (44 sites)

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VERY POOR CORRELATIONS


HORIZONTAL DISPLACEMENT yo @ Hou/3

yo = 2 Ho / lo K for L > 3loyo = 4 Ho / L K for L < lo

Ho = Hou/3 = horizontal load at ground surfaceK = 2.3 Eo = horizontal modulus (line load/deflection)

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INTERACTION DIAGRAM FOR COMBINED HORIZ. LOAD AND OVERTURNING MOMENT

ANY COMBINATION OF H AND M ON THE DIAGRAM GIVES THE SAME DEFLECTION

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y0(t)/yo(to) = (t/to)n

n = 0.01 to 0.03 in sandsn = 0.02 to 0.08 in clays

LONG TERM LATERAL LOAD


ΔR(t)/ΔR(to) = (t/to)-n

n = -log(ΔR(t)/ΔR(to) / log(t/to)

n = 0.01 to 0.03 in sandsn = 0.02 to 0.08 in clays

n VALUES FROM PMT TESTS

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yN = y1 N a

a averages 0.1 for clays (one way and two way)

a averages 0.08 for sands under one way loading

a averages 0 for sands under two way loading

CYCLIC LATERAL LOAD

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ΔRN/ΔR1 = N a

a = log (ΔRN/ΔR1) / log N

PMT only applicable to one way cyclic loading

a FROM PMT TESTS


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LATERAL LOAD NEAR A TRENCH

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Htrench = λ Hno trench

λ


BRIAUD, J.L., “SALLOP: Simple Approach for Lateral Loads on Piles,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 123, No. 10, pp. 958-964, ASCE, New York, October 1997.

BRIAUD, J.L., The Pressuremeter, A. A. Balkema, Rotterdam, Netherlands, 1992.

For more informationFor more informationOn Laterally Loaded PilesOn Laterally Loaded Piles

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TIEBACK WALLS


EARTH PRESSURE COEF. Vs MOVEMENT / HEIGHT

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BRIAUD J.-L., LIM Y., “Tieback Walls in Sand: Numerical Simulation and Design Implications,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 125, No. 2, pp. 101-111, February 1999, ASCE, Reston, Virginia.

BRIAUD, J.L., KIM, N.K., Beam Column Method for Tieback Walls, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 124, No. 1, ASCE, New York, January 1998.

BRIAUD, J.L., POWERS, W.F., WEATHERBY, D.E., “Should Grouted Anchors Should Have Short Tendon Bond Length”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 124, No. 2, ASCE, New York, February 1998.

For more informationFor more informationOn Tieback WallsOn Tieback Walls







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THIS BEARING CAPACITY EQUATIONTHIS BEARING CAPACITY EQUATIONDOES NOT WORKDOES NOT WORK

12u c qp cN BN DNγγ γ= + +

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, , , UL Cr p q N s=up kr=

THIS BEARING CAPACITY EQUATIONTHIS BEARING CAPACITY EQUATIONDOES WORKDOES WORK


3mx3m Footing Load Tests up to 1200 tonsTexas A&M National Site

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3mx3m Footing Load Tests up to 1200 tonsTexas A&M National Site


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s/B = 0.24 ΔR/R

pf = Γ pp

LOAD SETTLEMENT CURVE METHODLOAD SETTLEMENT CURVE METHOD


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BRIAUD J.-L., 2007, “Spread Footings in Sand: Load Settlement Curve Method”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. XXX, No. XX, yyyyy 2007, ASCE, Reston, Virginia.

BRIAUD J.-L., GIBBENS R., “Behavior of Five Spread Footings in Sand,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 125, No.9, pp. 787-797, September 1999, ASCE, Reston, Virginia.

BRIAUD J.-L., LI Y., RHEE K., 2006, “BCD: A Soil Modulus Device for Compaction Control”, Journal of Geotechnical and Geoenvironmental Engineering, Vol 132, Number 1, January 2006, ASCE, Reston, Virginia, USA.

For more informationFor more informationon Spread Footingson Spread Footings

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The San Jacinto MonumentCase History


History

• March 2, 1836: Independence declared• March 6, 1836: The Battle of The Alamo • April 21, 1836: The Battle of San Jacinto

General Santa AnnaGeneral Sam Houston

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History

Picture of Alfred Finn obtained from SloaneGallery.comPicture of Robert Cummins obtained from (Cummins, 1944)Picture of Raymond Dawson provided by Steve Wright, UT (2005)

Raymond F. DawsonGeotechnical Consultant

Alfred C. FinnArchitect

Robert C. CumminsStructural Engineer


From the Air

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SAN JACINTO MONUMENTHOUSTON (1936)

WASHINGTON MONUMENTWASHINGTON DC (1887)


Dimensions

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Construction


Loading

• Gross pressure = 224 kPa• Max pressure (dead + wind) = 273 kPa• Excavation = -83 kPa• Net pressure = 141 kPa• Net pressure after mat poured = 10 kPa• Pressure from Terraces = 34 kPa & 85 kPa

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Stratigraphy


Soil Index Properties

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Consolidation Characteristics


Modulus of Elasticity

Using the elastic settlement equation,s = 0.88(1-ν2)pB/E

the Modulus (E) at the site was back-calculated to be 12.3 MPa based on the last known settlement observation (s) of 0.329 m. – ν = 0.35– p = 138.9 kPa (net pressure)– B = 37.8 m

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Modulus of Elasticity


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Stress Distributions

1 8 .9 m

3 7 .2 m

5 5 .5 m

2 B ( B = 3 7 . 8 m )

2 .5 B ( B = 3 7 . 8 m )

ACE

OBD

ACE

OBD

1 8 .9 m

3 7 .2 m

5 5 .5 m

2 B ( B = 3 7 . 8 m )

2 .5 B ( B = 3 7 . 8 m )

ACE

OBD

ACE

OBD

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Depth of Influence

• Two definitions for the depth of influence:– Depth at which the pressure has decreased to 10%

of the applied surface pressure– Depth at which the settlement is 10% of the

settlement at the surface• The zone of influence depends on which

definition is used and on the modulus profile of the soil


Depth of Influence

Using StressCriterion

Using SettlementCriterion

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Depth of Influence

Zi/B vs E1/E0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.001 0.01 0.1 1 10 100 1000

E1/E0

Zi/B

E=0.1Z+400

E=Z+350

E=3.13Z+250

E=12.5Z+150

E=25Z+100

E=37.5Z+50

E=75Z+10

E=150Z+3


Case 7• Assumptions:

– Water at base of foundation– Added Fill– No rebound

0.390.34c L0.340.27b L0.520.45c0.460.37b0.370.32as (m)s (m)

Sub-Case

(FLEXIBLE Foundation)(RIGID Foundation)

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Case 8• Assumptions:

– Water at base of foundation– Added Fill– Rebound from excavation

0.640.54c L0.590.49b L0.960.81c0.900.75b0.610.52as (m)s (m)Sub-Case

(FLEXIBLE Foundation)(RIGID Foundation)


Reference Points

• Dawson established 50 reference points around the foundation

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Benchmarks-6.7 m deep


Actual Settlement

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Summary of Settlement

0.329Measured Settlement

0.187Dawson's Prediction

0.370Case 7a

0.607Case 8a

s (m)Description


Subsidence

Picture obtained from www.ruf.rice.edu/ ~leeman/aNR.html

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Subsidence

• The areas that have the greatest groundwater extraction have subsided about 3 m.

• The rate of subsidence in the Houston area ranges from 31 to 76 millimeters per year.

• Assuming uniform subsidence around the San Jacinto Monument, the benchmarks and reference points would not see differential settlement.


Lessons learned from this case history

1. For rigid mats, use flexible stress increase solutions and go to 2B

2. Use the void ratios from the consolidation curves s = H Δe/(1+eo)

3. Calculate separately the rebound during excavation, the settlement of the mat, the settlement of the structure.

4. For long term settlement, E/su ~ 123 (Eo(pmt)/su ~ 100)

5. Which settlement is important? After the mat is poured, after a few floors, after completion of the structure? Should the recompression settlement be included?

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THANK YOU

http://http://ceprofs.civil.tamu.edu/briaudceprofs.civil.tamu.edu/briaud//

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