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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
Jean-Louis BRIAUD – Texas A&M University
•ASCE MET Section and Geo-Institute Local Chapter
•Geoff Meyerhof (too complicated!)
•Louis Briaud (so what!)
ACKNOWLEDGEMENTSACKNOWLEDGEMENTS
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Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
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Jean-Louis BRIAUD – Texas A&M University
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
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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
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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
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Jean-Louis BRIAUD – Texas A&M University
MAXIMUM FRICTIONFOR PILES IN CLAY (short term and long term)
fmax = αSu fmax = βσ’ov
Jean-Louis BRIAUD – Texas A&M University
MAXIMUM FRICTION FOR PILES IN SANDfmax = βσ’ov
fmax (kPa) = 5 (N)0.7
N = SPT blow count
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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
FINDING THE DEPTH OF THE NEUTRAL POINT
Vertical Equilibrium
Qt + Fn = Fp + Qp
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
FINDING THE PILE SETTLEMENT
Wpile at top = wpile at bottom + elastic compression
Jean-Louis BRIAUD – Texas A&M University
FINDING THE LOAD SETTLEMENT CURVE
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Jean-Louis BRIAUD – Texas A&M University
FINDING THE LOAD SETTLEMENT CURVE
Jean-Louis BRIAUD – Texas A&M University
FINDING THE LOAD SETTLEMENT CURVE
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Jean-Louis BRIAUD – Texas A&M University
DOWNDRAG ON PILE GROUPS
Jean-Louis BRIAUD – Texas A&M University
DOWNDRAG ON PILE GROUPS
After Okabe, 1977
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Jean-Louis BRIAUD – Texas A&M University
DOWNDRAG ON PILE GROUPS
Jean-Louis BRIAUD – Texas A&M University
DOWNDRAG ON PILE GROUPS
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Jean-Louis BRIAUD – Texas A&M University
REDUCTION
FACTORS FOR
DOWNDRAG ON
PILE GROUPS
Jean-Louis BRIAUD – Texas A&M University
EXAMPLE
Pile Ult. Capacity
Qu = 706 + 1000
Qu = 1706 kN
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Jean-Louis BRIAUD – Texas A&M University
wtop = 46 mm wtop = 14 mm wtop = 14 mmwith bitumen
Jean-Louis BRIAUD – Texas A&M University
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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
HOW DOES BITUMEN BEHAVE?
Bitumen is a viscous material τ = η (dγ/dt)
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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 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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Jean-Louis BRIAUD – Texas A&M University
HOW TO CHOSE A BITUMENT THAT WORKS?
τ = η (dγ/dt)
• Storing
• Driving
• Reducing downdrag
• Particle penetration
SOIL
Jean-Louis BRIAUD – Texas A&M University
HOW TO CHOSE A BITUMENT THAT WORKS?
τ = η (dγ/dt)
• Storing
• Driving
• Reducing downdrag
• Particle penetration
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Jean-Louis BRIAUD – Texas A&M University
AVERAGE ANNUAL AIR TEMPERATURE = SOIL TEMPERATURE
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)
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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)
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Jean-Louis BRIAUD – Texas A&M University
Applying the bitumen (10 mm thick)
Jean-Louis BRIAUD – Texas A&M University
Handling in the field
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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)
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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
LATERAL LOAD-DEFLECTION CURVE
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
THE TEXAMPRESSUREMETER1981
SimpleSafeVersatile
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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
SAND (36 sites)
Jean-Louis BRIAUD – Texas A&M University
CLAY (44 sites)
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VERY POOR CORRELATIONS
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
ΔRN/ΔR1 = N a
a = log (ΔRN/ΔR1) / log N
PMT only applicable to one way cyclic loading
a FROM PMT TESTS
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
LATERAL LOAD NEAR A TRENCH
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Jean-Louis BRIAUD – Texas A&M University
Htrench = λ Hno trench
λ
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
TIEBACK WALLS
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EARTH PRESSURE COEF. Vs MOVEMENT / HEIGHT
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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
THIS BEARING CAPACITY EQUATIONTHIS BEARING CAPACITY EQUATIONDOES NOT WORKDOES NOT WORK
12u c qp cN BN DNγγ γ= + +
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Jean-Louis BRIAUD – Texas A&M University
, , , UL Cr p q N s=up kr=
THIS BEARING CAPACITY EQUATIONTHIS BEARING CAPACITY EQUATIONDOES WORKDOES WORK
Jean-Louis BRIAUD – Texas A&M University
3mx3m Footing Load Tests up to 1200 tonsTexas A&M National Site
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Jean-Louis BRIAUD – Texas A&M University
3mx3m Footing Load Tests up to 1200 tonsTexas A&M National Site
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
s/B = 0.24 ΔR/R
pf = Γ pp
LOAD SETTLEMENT CURVE METHODLOAD SETTLEMENT CURVE METHOD
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
The San Jacinto MonumentCase History
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
From the Air
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Jean-Louis BRIAUD – Texas A&M University
SAN JACINTO MONUMENTHOUSTON (1936)
WASHINGTON MONUMENTWASHINGTON DC (1887)
Jean-Louis BRIAUD – Texas A&M University
Dimensions
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Jean-Louis BRIAUD – Texas A&M University
Construction
Jean-Louis BRIAUD – Texas A&M University
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
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Soil Index Properties
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Jean-Louis BRIAUD – Texas A&M University
Consolidation Characteristics
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
Modulus of Elasticity
Jean-Louis BRIAUD – Texas A&M University
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Jean-Louis BRIAUD – Texas A&M University
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
Depth of Influence
Using StressCriterion
Using SettlementCriterion
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Jean-Louis BRIAUD – Texas A&M University
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
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
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)
Jean-Louis BRIAUD – Texas A&M University
Reference Points
• Dawson established 50 reference points around the foundation
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Jean-Louis BRIAUD – Texas A&M University
Benchmarks-6.7 m deep
Jean-Louis BRIAUD – Texas A&M University
Actual Settlement
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Jean-Louis BRIAUD – Texas A&M University
Summary of Settlement
0.329Measured Settlement
0.187Dawson's Prediction
0.370Case 7a
0.607Case 8a
s (m)Description
Jean-Louis BRIAUD – Texas A&M University
Subsidence
Picture obtained from www.ruf.rice.edu/ ~leeman/aNR.html
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Jean-Louis BRIAUD – Texas A&M University
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.
Jean-Louis BRIAUD – Texas A&M University
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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Jean-Louis BRIAUD – Texas A&M University
•Research Principles
•Downdrag on Piles
•Laterally Loaded Piles
•Spread Footings on Sand
•Large Mat on Stiff Clay
Jean-Louis BRIAUD – Texas A&M University