03 Implementation of pile design in the UK …

1 1 Implementation of pile design in the UK David BeadmanByrne Looby PartnersImplementation of pile design in the UKPile design in the UKStatic load testsGround test results-method of profiles- alternative methodAlternative proposalConclusionsBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David Beadman2 pile design in the UKTypical pile typeDiameterContinuous flight auger piles (cfa)300-1200mmBored piles6002400mmDesign largely by specialist contractors under competitive conditionsPiles designed for each different load to nearest (illtt01)Bored piles600-2400mmMinipiles140-600mmDriven precast / driven cast-in-situ / driven tubesBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David Beadman(occasionally to nearest ) pile design based on characteristic ground strength parametersFactors of Safety before Eurocode 7 LDSA (1999) Table 1 PreliminaryRequirements for loadFactor ofPreliminary pile Load Te s tRequirements for load testing of working piles ( x working load)

2 Factor of Safety FNoNo load testing on working testing on 1% of working sLoad testing on 1% of20 BGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanYe sLoad testing on 1% of working design to Eurocode 7 and the UK National Annex Andrew J. Bond and Brian Simpson (2009-10)Eurocode 7 in the UKPart 1: Eurocode 7, Ground Engineering, vol. 42, no 12, Dec 2009, pp27-31, London: Emap InformPart 2: UK National Annex, Ground Engineering, vol. 43, no 1, Jan 2010, pp28-31, London: Emap Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David National Annex design Approach 1 For axially loaded piles and anchorsCombination 1: A1 + M1 + R1 Combination 2: A2 + (M1 or M2) + R4We all had the opportunity to comment onCombination 2M1 - resistances of piles or anchorsM2 - unfavourable actions on piles negative skin frictioncomment on these proposals unfortunately most of us didn t!

3 BGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanWhy do we not factor the soil strength as for other structures?Combination 1: A1 + M1 + R1 Combination 2: A2 + M2 + R14 National Annex Table Partial resistance factors ( R) for bored piles for the STR and GEO limit statesResistanceSymbolSetR1R4 without explicit verification of SLSA)R4 with explicit verification of SLSA)verification of SLSA)verification of SLSA)Base (compression) (compression) in tension s; Explicit verification of the SLS -load tests (preliminary and/or working) carriedBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanExplicit verification of the SLS -load tests (preliminary and/or working) carried out on more than 1% of the constructed piles to loads not less than times the representative load for which they are R1 factors to means that Combination 1 is not critical for pile lengthTerminology explicit verification of SLS is rather clumsyStatic load tests (7)PRc;k= Min{(Rc;m)mean/ 1;(Rc.}

4 M)min/ 2}National Annex Table factors ( ) to derive characteristic values of the resistance of axially loaded piles from static pile load tests (n number of tested piles) for n =12345 Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanIn the UK we have increased these correlation factors compared to Annex A5 Static load tests (7) to do more than one preliminary pile test on a site (these are assumed to be preliminary pile tests)2No guidance on how to compare piles guidance on how to compare piles of different diameter or different (and others) have read this methodology as a means of determining the characteristic resistance from pile tests when the tests are used to confirm design using ground strength parameters.

5 (I understand this is incorrect) are not generally designed from pileBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David are not generally designed from pile tests alone. The pile test is used to confirm the design using ground strength parametersTHIS METHOD IS OF MINIMAL USE IN THE UKGround test results (5)PMethod of profilesRc;k= (Rb;k+ Rs;k)= Rb;cal+ Rs;cal= Rc;cal= Min{(Rc;cal)mean.(Rc;cal)min} 3 4 National Annex Table 3 4 Correlation factors ( ) to derive characteristic values of the resistance of axially loaded piles from ground test results (n the number of profiles of tests) for n=12345710 Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David Beadman Does not involve the use of a characteristic design line I understand this method is for use with CPT profiles (this is not generally used in the UK) Potentially dangerous if a profile is adopted from limited SPT or cudata It should be clearly stated as being limited for use with CPT profiles6 Ground test results (8)

6 Alternative Procedure (Eqn )Rb;k= :kand Rs;k= As; ;i;kNational Annex factor should be , except that it may be reduced to if the resistance is verified by a maintained load test taken to the calculated, unfactored ultimate is the way we are designing piles in the UKEffectively four sets of partial factorsBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanEffectively four sets of partial factorsRisk is that the model factor is omitted and the pile design is unsafeProposed AmendmentFor axially loaded piles and anchorsCombination 1: A1 + M1 + R1 Combination 2: A2 + M2 + R1 For piles only:For piles only.

7 Combination 1 is for STR Combination 2 is for GEOSoil parameterSymbolSetM1M2A)Partial factors for soil parameters ( M) for the STR and GEO limit stateBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanAngle of shearing resistanceA) cohesion c shear strength strength Amendment Table resistance factors ( R) for bored piles for the STR and GEO limit statesResistanceSymbolR1 Base 20 Base (compression) (compression) in tension s; the complication of R4 and two sets of R4 in each tableBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanProposed AmendmentDesign Resistance factor ( Rd)for the GEO limit statePile testing RdNo pile of working piles (to x representative load)

8 And 1% of working Rdis omitted, design is safeEnsures that both working pile testing and preliminary pileBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanEnsures that both working pile testing and preliminary pile testing are encouraged with additional economy8 Eurocode 7 - Ground test resultsAlternative ProcedureCombination 2 for pile lengthA2 + (M1or M2) + R4 ProposedA2 + M2 + R1 Action Factors- x Permanent Actions- x Variable ActionsMaterial Factors - (set M1)RitFt16/14Sh ftF Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David BeadmanResistance Factors Shaft Factor(for bored piles)- Base FactorModel Factor- 7 - Ground test resultsAlternative ProcedureCombination 1 for pile structural designAction Factors- x Permanent Actions- x Variable ActionsMaterial Factors - (set M1)Resistance Factors - Shaft Factor(fbd il )20BF tBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David Beadman(for bored piles) Base Factor(these resistance factors are not applied to structural design )

9 9 Global factor of safety for replacement piles(with 25% variable action) Method Overall FOS CurrentlyComparison between equivalent global factor from UK NA to EN 1997-1 and traditional UK practice, after Bond and Harris (2008) = Qult / QaNo explicit SLS checkTests on 1% working pilesPreliminary load testsBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David factor of safety drained factor of safetyNo testingWorking pile testsWorking and preliminary pile tests10m deep pile drained analysisBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David of factor of safety undrained factor of safetyNo testingWorking pile testsWorking and preliminary pile tests10m deep pile undrained analysis Ollftfftd tBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David shear strengthOverall

10 Factor of safety does not vary with undrained shear strengthConclusions Current pile design method is inconsistent with the rest of the document design from static load tests is rarely done in the UK without ground test results The method of profiles is not generally used in the UK The alternative method is used in the UK An alternative methodology for pile design and a set of partial ft h bdBGA Symposium on Eurocode 7 Today and Tomorrow23 March 2011 David Beadmanfactors have been propos