Pile Design To BS EN 1997-1:2004 (EC7) And The National Annex

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Geotechnical Design to EC713 January 2017Pile Design to BS EN 1997-1:2004 (EC7)and the National AnnexChris Raison BEng MSc CEng MICE MASCERaison Foster Associates Tel: Mob: E-Mail: Address:024 7641 033807974 005990chris@raisonfoster.co.uk7 Riverford CroftCoventryCV4 7HB Web Site:www.raisonfosterassociates.co.uk1

Geotechnical Design to EC713 January 20172

Geotechnical Design to EC713 January 2017What am I going to talk about? Concentrate on Practical ApplicationsBrief Review of theTraditional Design ApproachWhat is Different in EC7?EC7 – Geotechnical Design: Part 1: Chapter 7 – PilesUK National Annex: Model FactorEC7 Design Method and Partial Factors3

Geotechnical Design to EC713 January 2017What am I going to talk about? Other Aspects of Pile Design Negative Shaft Friction Horizontal Load Structural DesignWorked Example for a Site In SuffolkConclusions4

Geotechnical Design to EC713 January 2017Some History & Background 1974-1975:First proposal to develop international codes1990:CEN (European Committee for Standardisation) set up2004:BS EN 1997-1 (Eurocode 7, Part 1) and its UK NationalAnnex were published5

Geotechnical Design to EC713 January 2017Some History & Background Other Eurocodes important for piling:BS EN 1997-1 – Geotechnical DesignBS EN 1990 – Basis of Structural DesignBS EN 1991-1-1 – Actions on StructuresBS EN 1992-1-1 – Design of Concrete StructuresPlus Execution Codes6

Geotechnical Design to EC713 January 2017Some History & Background April 2010:Most geotechnical standards and Codes of Practice werewithdrawnEurocodes became the current standardsThe use of Eurocodes mandatory on public sector workOctober 2013:Part A of Building Regulations updated to refer toEurocodes (England)7

Geotechnical Design to EC713 January 2017Some History & Background June 2015:British Standards re-issued:BS8004 – FoundationsBS8002 – Retaining StructuresBS8081 – Grouted AnchorsNow fully compliant with Eurocodes[It was not originally intended to re-write these standards!]8

Geotechnical Design to EC713 January 2017Some History & Background Today:All public sector and most private sector constructionschemes are designed to EurocodesThe UK piling industry has taken on board the use ofEurocodes but with some reluctance9

Geotechnical Design to EC713 January 2017Behaviour of PilesE ND BEA RINGP ILE ON ROCKF RIC TIO N P ILET ENS ION PILES ETTL ING SOIL(DO WN DR AG)L ATERALLOAD10

Geotechnical Design to EC713 January 2017B ri dgea b u tmentE mb an km entL TPS INGLEPILEBELOWC OL UMNG ROU P OFPILESBELOWC OL UMNP ILE D R AFTT O B UIL DINGP ILE D B RIDGEA BU TM EN T ANDA PPROACHE MBAN KMENT11

Geotechnical Design to EC713 January 2017Piling Methods – Driven12

Geotechnical Design to EC713 January 2017Piling Methods – Rotary Bored or CFA13

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004 In the past, piles were driven to a refusalSelf-evident that the pile resistance is proportional to the driveenergyEvery driven pile has some sort of test – drive blowsBut this does not work for bored or drilled piles as there is nofeedback from installation14

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004 Static load testing is very attractive for designBut testing can be uneconomic and time consuming: Complex variable ground conditions Variable loading Difficult to deal with NSF Difficult to deal with changes to vertical stressPile designers therefore looked at calculation based ontheoretical soil mechanics15

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004L aye r 1L1Qs1U ltim ate pile res is ta nceQL aye r 2L aye r 3LL2Qs2Qs3u Qs Qb3Qb16

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004 The usual approach is to divide the ground into layers andassign ground parameters to each layer For bearing capacity, this is just φ’, c’, Cu and UCS From these we get Nc, Nγ and Nq for bearing capacity17

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004 Basic calculation method:18

Geotechnical Design to EC713 January 2017Traditional Pile Design to BS 8004 Factor of Safety varied between 2.0 and 3.0 for compressionloads and 3.0 for tensionActual FoS dependent on quality of GI, prior knowledge ofground conditions and whether preliminary non-working loadtests or contract proof load tests were carried out19

Geotechnical Design to EC713 January 2017Pile Design to EC7 So what is different?EC7 method is a Limit State Design method: Ultimate Limit State (ULS) States associated with collapse, structural failure, excessivedeformation or loss of stability of the whole of the structureor any part of itServiceability Limit State (SLS) States that correspond to conditions beyond which specifiedservice requirements are no longer met20

Geotechnical Design to EC713 January 2017Some Ultimate Limit States for PilesB earing ca pacityfailu re(co mp re ssio n)P ull-ou t fa ilure(te nsio n)Rota tion(la te ra l load)S tructu ra l fa ilureb y crushing(co mp re ssio n)S tructu ra l fa ilure(te nsio n)S tructu ra l fa ilurein be nding(la te ra l load)S tructu ra l fa ilureb y bu ckling(co mp re ssio n)S tructu ra l fa ilurein sh ear(la te ra l load)S tructu ra l fa ilurea t pile capconne ctionP eat21

Geotechnical Design to EC713 January 2017Some Serviceability Limit States SettlementTiltingCrackingUneven floor settlement22

Geotechnical Design to EC713 January 2017EC7 Limit States EC7 Adopts five distinct ultimate limit states: EQU – Loss of equilibrium (tilt or rotation) STR – Internal failure or excessive deformation[Strength of structural material is significant] GEO – Failure or excessive deformation of the ground[Strength of soil or rock is significant]UPL – Uplift or buoyancy HYD – Hydraulic heave, erosion or pipingSTR and GEO most important for pile design 23

Geotechnical Design to EC713 January 2017EC7 Design Approach Separation of ULS and SLS conditionPermanent and variable actionsFavourable and unfavourable actionsUse of characteristic ground propertiesUse of several partial factorsPartial factors avoid failure but not necessarily movement24

Geotechnical Design to EC713 January 2017EC7 Design Approach Basic inequality to be checked: Ed is the design value of the effect of all the actionsRd is the design value of the corresponding resistance of theground or structureFor pile design, this inequality compares the design action Fd(usually load) against the design resistance Rd 25

Geotechnical Design to EC713 January 2017EC7 Design Approach Design values of Ed, Rd are obtained by applying sets ofpartial factors to their characteristic values, Ek, RkEC7 allows three design approaches which use differentpartial factor setsEach country specifies its design approach in its NA DA1: UK, PortugalDA2: France, Germany, Poland, Spain .DA3: Denmark & NetherlandsSome countries allow more than one approach (Ireland, Italy)26

Geotechnical Design to EC713 January 2017UK National Annex UK has adopted Design Approach 1 - DA1This requires two calculations: A1 R1 M1R4 A2 M1/M2Combination 1Combination 2(Use M1 for calculating resistances and M2 for unfavourable actions such as NSF) For Combination 1, partial factors 1.0 are applied to theactions only - this does not usually control pile lengthFor Combination 2, partial factors 1.0 are applied toresistances with smaller factors applied to variable actions27

Geotechnical Design to EC713 January 2017Design Actions Fd Fd is the design action Frep is the representative action (usually load) Gk is the characteristic permanent actionQk is the characteristic variable actionAk is the characteristic accidental actionψ is the factor for combination of variable actions28

Geotechnical Design to EC713 January 2017Effect of Actions Ed Ed is the design value of the effect of all the actions: Frep is the representative action (usually load)Xk is the characteristic value of the material propertyad is the design value of a geometrical propertyγF and γm are relevant partial factors 29

Geotechnical Design to EC713 January 2017Effect of Actions Ed Design values: Frep is the representative action (usually load)Xk is the characteristic value of the material propertyad is the design value of a geometrical propertyγF and γm are relevant partial factors 30

Geotechnical Design to EC713 January 2017UK National Annex Local requirements specified in the UK National AnnexIn the UK this involves two separate calculations with differentcombinations of partial factors: Combination 1: Partial factors applied to actions; Ground strengthsand resistances are not factoredCombination 2: Partial factors applied to ground strengths,resistances and variable actions; Permanent actions are unfactoredNOTE for pile design, we factor ground resistances and notground strengths31

Geotechnical Design to EC713 January 2017Partial Factors on ActionsActionPermanentVariableUK NA Factor SetEC7 Factor es:1. Factors can be applied to Actions or the Effect of Actions.2. Factors given above are for buildings which remain unchanged from EC7 values3. Combination factors for actions that can exist simultaneously are given in theUK NA to BS EN 1990.4. There are a wider range of factors for bridges.32

Geotechnical Design to EC713 January 2017Pile Design to EC7 Static load testsGround tests (using direct correlations), e.g. CPT or PMTDynamic impact tests, e.g. CAPWAPStatistical corrections required to account for number of testresults (correlation factor)EC7 concentrates on pile design by testing.There is little reference to design by calculation – the normalUK approach!33

Geotechnical Design to EC713 January 2017Pile Design Methods Covered by EC7Design methodInformation usedConstraintsTestingStatic load testsValidity must be demonstrated bycalculation or other meansGround test resultsDynamic load testsCalculationEmpirical or analytical calculationmethodsObservationObserved performance ofcomparable piled foundationsValidity must be demonstrated bystatic load tests in comparablesituationsMust be supported by the results ofsite investigation and ground testing34

Geotechnical Design to EC713 January 2017Pile Design to EC7 The most common method for design method in the UK isdesign by calculationPile load testing is used mostly for verification of the designGround tests are used to select soil properties35

Geotechnical Design to EC713 January 2017Calculation Based on Soil Parameters Design can be based on measured φ’, c’, Cu and UCS usuallyfrom laboratory testing of undisturbed samples More common to use empirical relationships between insituCPT, SPT, PMT and other measurements to estimate theseparameters We can measure G, Eu and E’ in the laboratory, but again it ismore common to use empirical relationships36

Geotechnical Design to EC713 January 2017Ground Characterisation EC7 says a lot about determining characteristic orrepresentative soil propertiesCautious estimate affecting the occurrence of the limit state Similar to BS 8002 and CIRIA 104Most engineers already adopt cautious estimatesEngineering judgement requiredStatistics can be applied, but is difficult because of the usual limitednumber of samples and test dataFor pile design, not a great deal of difference between soilparameters for EC7 design compared to BS 8004 design37

Geotechnical Design to EC713 January 2017London Clay, cohesion v 00 150 200 250 300 350 400 450Undrained cohesion, cu (kPa)CAUTIOUSESTIMATE (?)44Reduced level (m)Reduced level (m)London Clay cohesion v depth161412050 100 150 200 250 300 350 400 450Undrained cohesion, cu (kPa)38

Geotechnical Design to EC713 January 2017Calculation Based on Soil Parameters Design is based on fundamental geotechnical groundparameters such as c’, φ’, G, E’, but could also include Cu,UCS and Eu for clays and rocksThese extend into derived parameters such as Nc, Nγ and Nqfor bearing capacity, Kq and Kc factors for horizontal loads onpiles or Ka, Kac, Kp and Kpc for ground retentionBut we also need some empirical factors such as Ks forgranular, α for clay, β for Chalk39

Geotechnical Design to EC713 January 2017So how do we estimate pile shaft frictionand end bearing from ground parameters? Effective Stress ApproachGranular Soils Total Stress ApproachCohesive or Rock (Weak Mudstone)40

Geotechnical Design to EC713 January 2017Standard Penetration Test – Granular Soils41

Geotechnical Design to EC713 January 2017Standard Penetration Test – Granular Soils42

Geotechnical Design to EC713 January 2017Standard Penetration Test – Clay SoilsCu f1 x (N)60f1 4.0 to 6.043

Geotechnical Design to EC713 January 2017Laboratory – Undrained Shear StrengthTriaxial Testing44

Geotechnical Design to EC713 January 201745

Geotechnical Design to EC713 January 2017Insitu Testing – CPTCu in claysΦ’ in granular soils46

Geotechnical Design to EC713 January 2017GI Using CPTC u qc / N kNk 15 to 30Nk 20 taken forGlacial Till in thisexample47

Geotechnical Design to EC713 January 2017Pile Shaft Friction Beta MethodSoft Soils or Chalk UCS MethodSandstone, Limestone or Strong Mudstone48

Geotechnical Design to EC713 January 2017Rock TestingPoint Load TestingUniaxial Compression Test49

Geotechnical Design to EC713 January 2017Pile End Bearing Effective Stress ApproachGranular Total Stress ApproachCohesive or Rock (Weak Mudstone)50

Geotechnical Design to EC713 January 2017Pile End Bearing51

Geotechnical Design to EC713 January 2017Pile End Bearing SPT MethodChalk UCS MethodSandstone, Limestone or Strong Mudstone52

Geotechnical Design to EC713 January 2017Design Soil Parameters Design values obtained by dividing the characteristic orrepresentative property by a partial factor Usual properties to be factored are strength [but stiffness mayneed to be factored for horizontal load design]Either effective stress strength, c’ and ϕ’, or undrained shearstrength cu, or unconfined compressive strength UCS for rocksFor pile design to the UK National Annex, factored design soilparameters are not used except for negative shaft friction 53

Geotechnical Design to EC713 January 2017Partial Factors on Soil ParametersSoil PropertyUK NA Factor SetEC7 Factor SetM1M2M1M2Friction Angle tan φ’1.01.251.01.25Effective Cohesion c’1.01.251.01.25Undrained Shear Strength Cu1.01.41.01.4Unconfined Strength UCS1.01.41.01.41.01.0Unit Weight γUK NA gives no factor for unit weight so presume 1.0; other factors remain unchanged.For pile design to the UK National Annex, factored design soilparameters are not used except for negative shaft friction54

Geotechnical Design to EC713 January 2017Pile Design to EC7 Based on Resistances For pile design, it is necessary to compare the design actionFd (usually load) against the design resistance Rd But note that this is now in terms of compression or tensionload and compression or tension resistance: As is usual, the design resistance Rc;d can be assumed to bethe sum of the end bearing and shaft design resistances:55

Geotechnical Design to EC713 January 2017Pile Design to EC7 Based on Resistances The design resistances Rc;d or Rt;d are obtained from thecharacteristic end bearing and shaft friction by using partialresistance factors56

Geotechnical Design to EC713 January 2017Pile Design to EC7 Based on Resistances The characteristic end bearing and shaft friction can becomputed using existing and recognisable methods either by: Calculation Static load testing Dynamic load testing Correlation with CPT or other insitu ground testing Design charts based on experience(e.g. EA-Pfähle used in Germany)57

Geotechnical Design to EC713 January 2017Pile Design by Calculation The characteristic base resistance and shaft resistance can becalculated from the characteristic end bearing and shaftfriction stresses as follows: These are similar to the approach used for BS 8004 butinclude an additional model factor γRd to ‘correct’ the partialresistance factors (applied to the characteristic resistances toobtain the design resistance Rc;d)58

Geotechnical Design to EC713 January 2017Pile Load Testing59

Geotechnical Design to EC713 January 2017 Pile Load Tests – Preliminary – To ULSResistance at10% diameter5,200kN Load test to ULS allows a lower model factor γRd to be used60

Geotechnical Design to EC713 January 2017Pile Shaft Friction Effective Stress Approach – Granular Total Stress Approach – Cohesive or Rock (Weak Mudstone) Beta Method – Soft Soils or Chalk UCS Method – Sandstone, Limestone or Strong Mudstone61

Geotechnical Design to EC713 January 2017Pile End Bearing Effective Stress Approach – Granular Total Stress Approach – Cohesive or Rock (Weak Mudstone) SPT Method – Chalk UCS Method – Sandstone, Limestone or Strong Mudstone62

Geotechnical Design to EC713 January 2017Partial Resistance Factors The design resistance Rd is obtained from the characteristicend bearing and shaft friction by using partial resistancefactors The partial resistance factors in the UK National Annex havebeen modified to take account of the type of pile and whetherthe serviceability behaviour is to be determined either by loadtest or a rigorous and reliable calculation63

Geotechnical Design to EC713 January 2017Partial Resistance Factors for Driven PilesComponentUK NA Factor SetEC7 Factor SetR1R4 (No SLS)R4 2.01.71.251.151.11.6Main differences for resistance factors relate to:1. Factor set R4 where different values depend on whether SLS behaviour is verified or not(test or calculation).2. Model factor to be applied to ground properties to derive characteristic values ordirectly to the calculated shaft or end bearing capacities.3. Model factor 1.4, but can be reduced to 1.2 if a load test is completed to calculatedunfactored ultimate resistance (ULS check).64

Geotechnical Design to EC713 January 2017Partial Resistance Factors for Bored PilesComponentUK NA Factor SetEC7 Factor SetR1R4 (No SLS)R4 .02.01.71.251.151.11.6Main differences for resistance factors relate to:1. Factor set R4 where different values depend on whether SLS behaviour is verified or not(test or calculation).2. Model factor to be applied to ground properties to derive characteristic values ordirectly to the calculated shaft or end bearing capacities.3. Model factor 1.4, but can be reduced to 1.2 if a load test is completed to calculatedunfactored ultimate resistance (ULS check).65

Geotechnical Design to EC713 January 2017Partial Resistance Factors for CFA PilesComponentUK NA Factor SetEC7 Factor SetR1R4 (No SLS)R4 02.01.71.251.151.11.6Main differences for resistance factors relate to:1. Factor set R4 where different values depend on whether SLS behaviour is verified or not(test or calculation).2. Model factor to be applied to ground properties to derive characteristic values ordirectly to the calculated shaft or end bearing capacities.3. Model factor 1.4, but can be reduced to 1.2 if a load test is completed to calculatedunfactored ultimate resistance (ULS check).66

Geotechnical Design to EC713 January 2017Equivalent Lumped FoSPile TypeDrivenEnd BearingDrivenEnd & ShaftBoredShaft Friction1.2.3.4.ActionsA21.11.11.1Resistance FactorsR4 (No SLS)1.71.7/1.51.6R4 (SLS)1.51.5/1.31.4ModelF

Pile designers therefore looked at calculation based on theoretical soil mechanics. 16 Geotechnical Design to EC7 13 January 2017 Layer 1 Layer 2 Layer 3 L 1 L 2 L 3 Q s1 Q s2 Q s3 Q b Ultimate pile resistance Q u Q s Q b Traditional Pile Design to BS 8004. 17 Geotechnical Design to EC7 13 January 2017 Traditional Pile Design to BS 8004 The usual approach is to divide the ground into .

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