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THE CURRENT PILING CODE AS 2159 -2009
SOME NEW CHANGES AND FEATURES
Gary Chapman Golder Associates Melbourne
GARY CHAPMAN
9/6/2010 1
THE NEED FOR A REVIEW
The Old code was dated 1995 and was over 14 years old and in need of updating
Concerns were raised by some contractors and consultants within the piling industry regarding pile testing and the incorrect selection of gfactors we now have a more rigorous selection system
New piling systems have become available over the last 14 years
Advances have been made in pile testing methods
9/6/2010 2
SAA COMMITTEE CE 018 MEMBERS
Prof Harry Poulos (chairman)Brian Chandler Dr Gary ChapmanDavid KlingbergPeter Mc Donald (co-opted)Jim MillarProf Mark RandolphDr Julian Seidel Slav TchepakDr Frank Collins
Coffey Geosciences, SydneyAECOM -Maunsell, MelbourneGolder Associates, MelbourneWagstaff Piling, BrisbaneDouglas Partners, MelbourneWaterway Const. SydneyUWAFoundation QA, MelbourneVibropile, SydneyMonash University, Melbourne
9/6/2010 3
OUTLINE OF CHANGES
New terminology S* is now EdCode structure similar to previous, new pile types recognised -jacked and steel screwed, cast insitu screw displacementGeotechnical design aspects g factor is now calculated not selected from a list, down drag calculations improvedStructural design aspects durability section revised, revised concrete placement factor Construction and testing aspects changes to pile testing acceptance criteria, some testing clauses are now normative (i.e. required) rather than there for guidance only, there is now recognition of benefits of testing by increasing the g factor with increasing amounts of testingTesting aspects recognition of alternative forms of testing such as Statnamic and Osterberg cell tests
9/6/2010 4
Code Structure Similar to previous with some changes
1. Scope and general2. Site investigation information required3. Design requirements & procedures4. Geotechnical design- strength and serviceability5. Structural design concrete and grout piles, steel, composite & timber piles6. Durability design7. Materials and construction requirements8. Testing- revised acceptance criteriaAppendices: Detailed testing procedures and requirements for static, O cell, high strain dynamic, rapid (Statnamic), and low strain and sonic integrity testing
9/6/2010 5
Section 2 - Site Investigations
The code now includes a requirement for site investigations to address working platform issues and the stability of a safe working platform for piling equipment.Clause 2.2(c) (xii) an assessment of the site surface for the provision of a safe work platform for piling equipmentTo help prevent this from happening
9/6/2010 6
Section 3 Design Requirements
Design for ultimate strength and for serviceabilityLoad factors for actions from ground movements for structural design
1.2 x negative skin friction (Fnf) action1.5 x compression, tension from vertical ground movement (Fes)1.5 x moment, shear and axial forces from lateral ground movement (Fem)1.5 x moments shears and axial forces from heave due to unloading from excavation (Feh)For geotechnical strength design, loads due to soil movements (e.g. down drag) do not need to be taken into account.For geotechnical serviceability design, loads due to soil movements (e.g. down drag) shall be taken into account using unfactored loads
9/6/2010 7
Section 4 - Geotechnical Design
A completely new section on the assessment of geotechnical design parametersA detailed process for the explicit determination of the geotechnical strength reduction factor gTangible benefits for conducting load testing through the testing benefit factorA revised treatment of negative skin friction at serviceability loads and a requirement for capacity in the stable zone to be verifiedGuidance for design of combined piled raft foundations
9/6/2010 8
Selecting the right geotechnical strength reduction factor
Underlying philosophy:Reduce ad-hoc judgement in the fg selection process available under previous code
Reduced maximum value of fg selection available from 0.9 to 0.76
You must now consider all of the site risks more specifically
There is an incentive for pile load testing by using the testing benefit factor to increase fgCan also allow for the benefits arising from the design of a redundant foundation system. Single piles are not redundant and now attract a reduced fg value for a low risk site rating fg is 0.67 for a non redundant system versus 0.76 for a redundant system.
9/6/2010 9
Design Geotechnical Strength
Design geotechnical strength (Rd,g) is calculated as the design ultimate geotechnical strength (Rd,ug) multiplied by a geotechnical strength reduction factor (fg)
Rd,g = fg . Rd,ug
fg, = fg,b + (ft,f fg,b).K fg,bwhere fg,b = basic geotechnical strength reduction factor
ft,f = intrinsic test factor 0.9 for static test, 0.85 Osterberg cell, 0.8 for PDA test on preformed piles, 0.75 for Statnamic and for PDA on other than preformed piles
K = testing benefit factor
9/6/2010 10
Basic Geotechnical Strength Reduction Factor fg,b
The value of fg,b depends upon the assessed site risk factors & the weighted sum of individual risks x risk weighting factors
Risk factors to be considered are divided into 3 categories:Site FactorsDesign FactorsInstallation Factors
9/6/2010 11
Individual Risk Ratings (IRR) Table 4.3.2B
RISK LEVEL INDIVIDUAL RISK RATING (IRR)
Very Low 1
Low 2
Moderate 3
High 4
Very High 5
9/6/2010 12
Basic Risk Factors
TABLE 4.3.2 (A)
Risk Category
Risk Factor Weighting factor
Site Geological complexity of the site 2
Extent of Ground Investigation 2
Amount & quality of geotechnical data 2
9/6/2010 13
Basic Risk Factors (continued)
TABLE 4.3.2 (A) (cont.)Risk
CategoryRisk Factor Weighting
factorDesign Experience with similar
foundations & conditions 1
Methods of assessing design parameters for design 2
Design Method Adopted 1
Methods of utilizing in-situ test data and installation data 2
9/6/2010 14
Basic Risk Factors (continued)
TABLE 4.3.2 (A) (cont.)
Risk Category
Risk Factor Weighting factor
Installation Level of construction control 2
Level of performance monitoring (during & after construction)
0.5
9/6/2010 15
Average Risk Rating
To calculate the Site Average Risk Rating (ARR)
ARR = S (wi. IRRi )/ S wiWhere wi = weighting factor for the individual risk factor consideredIRR = Individual risk rating which is selected based on 1 = very low risk through to 5 = very high risk.Example: A site investigation for piling where the bores stop above expected pile toe level = very high risk geotech data then IRR = 5 for site quality of data and possibly also for extent of investigation as well.
9/6/2010 16
Examples Individual Risk Circumstances
Geological complexity of site. IRR 1 = horizontal well defined strata, IRR 3 = some variability, IRR 5 highly variable profile steeply dipping rock
Design Method Adopted. IRR 1 = well established and soundly based methods, IRR 3 = simplified methods with a well established basis, IRR 5 simple empirical methods or sophisticated methods that are not well established.
Installation. IRR 1 = detailed construction control with professional geotechnical engineering supervision with well established processes, IRR 3 = limited professional supervision with conventional procedures, IRR 5 = very limited or no involvement of designer with construction processes that are not well established or complex.
9/6/2010 17
Sample Average Risk Rating Calculation
Risk Factor (wi) IRR Wi . IRR
Geological Site Complexity 2 3 6Extent of Site Investigation 2 4 8
Amount & Quality of Geotech Data 2 4 8Experience with similar foundations 1 2 2Method of Parameter assessment 2 3 6
Design Method Adopted 1 3 3Method of using Insitu/Install data 2 3 6
Level of Construction Control 2 3 6Level of Performance Monitoring 1 4 4
Sums 15 49ARR = S (wi. IRRi )/ S wi 3.27
9/6/2010 18
Selection of basic geotechnical strength reduction factor fg,b
Range of ARR
Overall Risk Category
fg,b for lowredundancy
fg,b for highredundancy
ARR
Geotechnical reduction factor - Benefit of pile load testing
fg = fg,b + (ft,f fg,b).K fg,bwhere fg,b = basic factor (0.56 in this example)
ft,f = intrinsic test factor depends of type of testing
K = testing benefit factor which depends on the amount of load testing carried out
9/6/2010 20
Intrinsic Test Factor
The intrinsic test factor (ft,f) is determined by the type of load testing proposedft,f = 0.9 for static load proof testing
= 0.85 for Osterberg cell testing= 0.8 for dynamic proof load testing (PDA) on
preformed piles= 0.75 for rapid proof load testing (Statnamic)= 0.75 for PDA testing of other than preformed piles= fg,b for no load testing
9/6/2010 21
Testing Benefit Factor K
For static, O cell, or rapid load testing
K= 1.33 p / (p + 3.3)
Testing Benefit Factor
Testing Benefit Factor
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50
% Piles Tested
Test
ing
Ben
efit
Fact
or
StaticDynamic
9/6/2010 23
Improveme