Lecture 16 - DF14 Static Analysis Based on Insitu...

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Unformatted text preview: DF14 Static Analysis Based on Insitu Measurements: CPT o CPT measures end bearing and side shear directly o Penetration is quasi-static, not dynamic not a good pile model o several methods including LPC program and Schmertmann/Nottingham method o limited by penetration capability, piles usually driven into strong soil SPT o dynamic insertion of sampler is model pile, good basis for correlation o does not separate end bearing and side shear o bearing on sampler dominates in sand and side shear dominates in clays o possible to guess approximate ratio of side shear to end bearing based on soil type o several methods, FDOT Bulletin 121-A by Schmertmann (1967) calibrated against static load tests FB-Deep (Previously SPT97) Program (available from www.bsi-web.ce.ufl.edu ) o program from FDOT Bulletin 121-B by Nottingham and Renfro (1967) o program updated by McVay, et al. at (1994) o pile capacity based on CPT soundings (UF, LCPC and Schmertmann methods) o side shear, f s vs. N and end bearing, q vs. N based on soil type and pile type (concrete, H-pile, steel pipe pile) o N < 5 assigned N = 0, N > 60 assigned N = 60 o method based on N 60 (safety hammer), program will correct for automatic hammer, must correct for other hammer energy efficiencies o P u = Q s + Q T- W DF15 Soil Type Description 1 Plastic clay 2 Clay-silt-sand mixtures, very silty sand, silts and marls 3 Clean sands 4 Soft limestone, very shelly sand 5 Void (No Capacity) o ultimate side shear fully mobilized at 0.1 - 0.3 movement o ultimate bearing requires much more movement, o popular Davisson failure criteria based on movement o pile capacity based on SPT found to correlate with Davisson failure at: (ultimate side shear + "mobilized" end bearing) = ultimate pile capacity where "mobilized end bearing" 1/3 of ultimate end bearing o unit end bearing at pile tip (and any other depth) = average of 8.0B above and 3.5B below pile tip: ( ) 2 / q q = q B 5 . 3 B 8 T + where q T = average, uncorrected unit end bearing at pile tip q B 8 = average of unit end bearing over 8B above pile tip (terminate end bearing average above tip at less than 8.0B if stronger bearing layer or ground surface is encountered) q B 5 . 3 = average of unit end bearing over 3.5B below pile tip o if the bearing layer is stronger than the layer above it, then end bearing is corrected for the depth embedment in the bearing layer, D A , if less than a critical depth, D C : Soil Type Description Critical Depth Ratio (D C /B) 1 Plastic clay 2 2 Clay-silt-sand mixtures, very silty sand, silts and marls 4 3 Clean sands (N 12) (12 < N 30) (N > 30) 6 9 12 4 Soft limestone, very shelly sands NA DF16 o no bearing correction if the overlying layer is stronger than the bearing layer o if D A < D C and overlying layer is weaker than the bearing layer, then the unit bearing is interpolated as follows: ) q- q ( D D + q = q LC T C A LC where q = corrected unit end bearing at pile tip q LC = unit end bearing at layer change...
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This note was uploaded on 09/12/2011 for the course CEG 4012 taught by Professor Staff during the Fall '08 term at University of Florida.

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Lecture 16 - DF14 Static Analysis Based on Insitu...

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