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Results Acknowledgements The assistance provided by ConeTec, Inc. in terms of partial funding for this research and access to the field data for different sites and Fugro in terms of access to the field data is gratefully acknowledged. References Berardi, R., & Bovolenta, R. (2005). "Pile-settlement evaluation using field stiffness non-linearity." Proc. Institution of Civil Engrg, Geotech. Engrg. 158(GE1): 35–44. LoadTest (2010). <http://www.loadtest.com/loadtest-usa/products/ >, accessed Oct. 30, 2010. Mayne, P.W. & Niazi, F.S. (2009). "Evaluating axial pile response from CPT." J. Deep Foundations Institute, 3(1): 3–12. Mayne, P.W. and Woeller, D.J. (2008). "O-cell response using elastic pile and seismic piezocone tests." Proc. of the BGA Int'l. Conf. on Foundations, Dundee, Scotland, June 24–27. Niazi, F.S. & Mayne, P.W. (2010). "Evaluation of EURIPIDES pile load tests response from CPT results." Intern. J. of Geoengineering Case Histories, 1(4): 367 – 386. Niazi, F.S., Mayne, P.W. & Woeller, D.J. (2010). "Drilled shaft O-Cell response at Golden Ears Bridge from seismic cone tests.“ ASCE GSP No. 198, Reston, VA: 452 – 469. Randolph, M.F. & Wroth, C.P. (1978). "Analysis of deformation of vertically-loaded piles." J. of Geotech. Engrg. Div., 104 (GT12): 1465–1488. Pile load test • Pile load test: highly instrumented test pile; for verifying the axial pile response • Osterberg load cell (O-cell): – hydraulically-driven, high capacity, sacrificial loading device – works in two directions, upward against Q s and downward against Q b – automatically separates Q s and Q b – multiple O-cells at different elevations enable staged testing of distinct elements Problem statement • Multiple CPT-based methods without optimal use of SCPTu readings • Existing methods mostly rely on q t reading for evaluating both Q s and Q b • Existing methods focus solely on axial “capacity” only • Most recent methods address driven pipe piles (in sand) • Considerable scatter in the estimated capacities from different existing methods • At least 42 different criteria defining “capacity” from pile load tests Research objectives • Database collection • Utilization of small-strain stiffness (G max ) • Application of Randolph analytical model: top-down pile load test • New application to Osterberg-cell load test • Calibration, verification, and reliability from the database • Seek improved direct SCPTu-based methods to include bored piles (for clays; silts, mixed soils, as well as sands) • Desire complete load-displacement-capacity response • Semi-empirical method matching field experience with analytical basis Methods Background • Deep foundations: commonplace for large scale projects • Conventional site characterization methods: time consuming, expensive, and tedious • Seismic Piezocone Penetration Test (SCPTu): – Expedient, economical and reliable in-situ method – Shear wave (V s ), tip stress (q t ), sleeve friction (f s ), & porewater pressure (u 1 or u 2 ) – Detailed stratigraphic information & soil engineering properties using correlations • Pile response to axial loading : – Ultimate design axial capacity (Q ult = Q t ) – Load transfer to the pile shaft (Q s ) and the base (Q b ) – Load-settlement response: w t vs. Q t , w t vs. Q s , w t vs. Q b and w b vs. Q b • Axial Pile Analysis via Indirect (Rational) and Direct CPT-based Methods • Elastic continuum framework (Randolph & Wroth 1978): load-displacement-capacity • Displacements vs. load levels starting from small strains up to the full capacities • Soil deformations for small strains via initial soil stiffness (G max ) from the V s readings • Non-linear soil stress-strain-strength response from modulus reduction algorithms • For homogeneous/Gibson-type soils, floating/end-bearing piles, compression/uplift Axial Pile Foundation Response from Seismic Piezocone Tests GRA: Fawad S. Niazi; Advisor: Dr. Paul W. Mayne School of Civil and Environmental Engineering, Georgia Institute of Technology, U.S.A. Figure 1. SCPTu sounding & Engineering parameters: Golden Ears Bridge site, (Niazi et al. 2010). Figure 3. Different arrangements of Pile Load Tests (LoadTest 2010). Figure 4. O-Cell Test Arrangement (modified after LoadTest 2010). Figure 2. Randolph Analytical Elastic Pile Model. Figure 7. Examples application of Randolph analytical pile model: (left) ACIP pile at University of Houston (Mayne & Niazi 2009), (right) compression and uplift load tests on driven pipe pile at EURIPIDES site, The Netherlands (Niazi & Mayne 2010). w t r o r b G max G SM G sL , G sb x, l, mL E p , L, r o , z Q t (w t ) Randolph Solution r E Stiffness Decay Curves Figure 5. Stiffness decay curve (modified after Berardi & Bovolenta 2005). NGES Texas A&M Clay, TX NGES Texas A&M Sand, TX NGES Texas Houston, TX NGES Amherst NGES Spring Villa, Opelika, AL NGES Northwestern Univ., IL Georgia Tech Campus CNN International Blvd. I 85 Bridge, Coweta, AL Golden Ears Bridge, BC Foothill Medical Center, AB High Prairie, AB EURIPIDES, Netherlands Rio de Janeiro, Brazil Swan River, Perth, Australia Grimsby Research Site, UK Cowden, UK www.mapcruzin.com Figure 6. Locations of current case studies Figure 8. Examples application of Randolph analytical pile model to O-cell load tests: (left) drilled shaft at I-17 Cooper River Bridge, Charleston, SC (Mayne et al. 2008), (right) drilled shaft at Foothills Medical Center, Calgary, AB (Mayne & Niazi 2009). 0 10 20 30 40 50 60 70 80 90 100 0 10 20 Depth (m) Tip q t (MPa) 0 0.1 0.2 0.3 Sleeve f s (MPa) 0 1 2 3 4 Porewater u 2 (MPa) u2 uo 100 200 300 400 Shear Wave V s (m/s) 15 16 17 18 19 20 Unit Weight, g t (kN/m 3 ) 20 25 30 35 40 Friction, f' (deg.) Sand Gravelly Sand Sand Mixture Sand Mixture Clay Organic Clay 0 1 2 3 4 5 Classification Index, I c 0 500 1000 1500 Preconsolidation Stress, s p ' (kPa) SCPT based (Mayne 2007) CPT based (Mayne et al. 2009) Effective Overburden Stress q c u 2 f s V s f s u 2 V s q c r o = D o /2 = pile radius r b = D b /2 = pile base radius h = r b /r o = geometric factor (bell-shaped) E p = pile modulus G sL =soil shear modulus at z=L G so = soil shear modulus at the pile top G sb = soil stiffness below the pile base G sM = soil shear modulus at mid-shaft r E = G sM /G sL = modulus variation factor n = Poisson’s ratio l = E p /G sL = pile-soil stiffness ratio x = G sL /G sb = soil stiffness at pile base z = ln(r m /r o ) = measure of influence radius r m = L{0.25 + x [2.5 r E (1 – n) – 0.25]} mL = 2(2/zl) 0.5 (L/D) = pile compressibility w ti = settlement at top of pile segment w i = settlement of individual pile segment w b = pile base settlement E b = soil Young’s modulus below pile base f p & q b = pile unit side & base resistance G so1 Layered soil load and settlement distribution: L 1 L 2 L 3 Layer 1 Layer 2 Layer 3 Q t1 =Q s1 =f p1 ∙p∙D 1 ∙L 1 w t1 = w t2 + w 1 Q t2 = Q s2 = f p2 ∙p∙D 2 ∙L 2 w t2 = w t3 + w 2 Q t3 = Q s3 + Q b Q t3 = f p3 ∙p∙D 3 ∙L 3 + Q b w t3 = w 3 +w b G sL1 G sL2 G so2 = G sb1 G so3 = G sb2 G sL3 G sb Compressible pile solution: Load transfer to base: Shaft load distribution: Q s =Q t – Q b Pile base displacement: G =G max ∙[1 – f(Q/Q t ) g ] Operational soil modulus: Pile Pile Length L G sL z = Depth Pile diameter D Q t G sb G sM Q b Q s G so Q t = Q b + Q s Q b = q b ∙p∙D 2 /4 Q s = (f pi ∙p∙D∙L i ) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.01 0.1 1 10 G SM / G max w t /D (%) G SM /G max = (5.81 X 10 2 w t /D + 0.80) -1 Encased telltale rod Hydraulic supply line Displacement transducers Osterberg cell O-cell Bearing plates Skin friction, f p Skin friction, f p Skin friction, f p End bearing, Q b = q b *A b Hydraulic control Movement transducers PC + data logger Reaction frame 0 50 100 150 200 250 300 350 -15 -10 -5 0 5 10 15 20 25 30 Top Displacement (mm) Axial Load (MN) Q t : Elastic Solution (C2) Q t : Elastic Solution (C1) Q s : Elastic Solution (C1) Uplift Q t : Elastic Solution (T) Compression Q b : Elastic Solution (C1) Measured 0 10 20 30 40 50 0 0.4 0.8 1.2 1.6 2 Top Displacement (mm) Axial Load (MN) Qtotal = Qs + Qb Predicted Qb Predicted Qs Measured Total Measured Shaft Measured Base -150 -100 -50 0 50 100 0 10 20 30 40 Displacement (mm) O-Cell Load (MN) Meas. Stage 1 Lower O-Cell: Load Down Meas. Stage 2 Upper O-Cell: Load Down Meas. Stage 3 Upper O-Cell: Load Up Shaft diameter d = 2.6 m L = 16.3 m L = 2.5 m L = 14.2 m L = 14.0 m 1 m 1 2 3 Upper O-Cell Lower O-Cell Casing 10 m 20 m 30 m 40 m 0 m Depth 48 m www.transportation.org -40 -20 0 20 40 60 80 0 1 2 3 4 5 6 7 8 Displacement (mm) O-Cell Load (MN) Loading Down Measured Below O-Cell Measured Above O-Cell Loading Up d = 1.4 m L = 10 m L = 4 m www.trotterandmorton.com
