AS2159

THE CURRENT PILING CODE AS 2159 -2009

SOME NEW CHANGES AND FEATURES

Gary Chapman Golder Associates Melbourne

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 φ_g factors – 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

SAA COMMITTEE CE 018 MEMBERS

„ Prof Harry Poulos (chairman) „ Brian Chandler

„ Dr Gary Chapman „ David Klingberg

„ Peter Mc Donald (co-opted) „ Jim Millar

„ Prof Mark Randolph „ Dr Julian Seidel „ Slav Tchepak „ Dr Frank Collins

„ Coffey Geosciences, Sydney „ AECOM -Maunsell, Melbourne „ Golder Associates, Melbourne „ Wagstaff Piling, Brisbane

„ Douglas Partners, Melbourne „ Waterway Const. Sydney

„ UWA

„ Foundation QA, Melbourne „ Vibropile, Sydney

OUTLINE OF CHANGES

„ Code structure – similar to previous, new pile types recognised

-jacked and steel screwed, cast insitu screw displacement

„ Geotechnical design aspects – φ_g factor is now calculated not selected

from a list, down drag calculations improved

„ Structural 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 φ_g factor with increasing amounts of testing

„ Testing aspects recognition of alternative forms of testing such as

Code Structure – Similar to previous with some changes

„ 1. Scope and general

„ 2. Site investigation – information required „ 3. Design requirements & procedures

„ 4. Geotechnical design- strength and serviceability

„ 5. Structural design – concrete and grout piles, steel, composite &

timber piles

„ 6. Durability design

„ 7. Materials and construction requirements „ 8. Testing- revised acceptance criteria

„ Appendices: Detailed testing procedures and requirements for static, O

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 equipment”

Section 3 Design Requirements

„ Load factors for actions from ground movements for structural design „ 1.2 x negative skin friction (F_nf) action

„ 1.5 x compression, tension from vertical ground movement (F_es)

„ 1.5 x moment, shear and axial forces from lateral ground movement

(F_em)

„ 1.5 x moments shears and axial forces from heave due to unloading

from excavation (F_eh)

„ For geotechnical strength design, loads due to soil movements (e.g.

down drag) do not need to be taken into account.

Section 4 - Geotechnical Design

„ A completely new section on the assessment of geotechnical design

parameters

„ A detailed process for the explicit determination of the geotechnical

strength reduction factor Φ_g

„ Tangible benefits for conducting load testing through the testing benefit

factor

„ A revised treatment of negative skin friction at serviceability loads and a

requirement for capacity in the stable zone to be verified

Selecting the right geotechnical strength

reduction factor

Underlying philosophy

„ Reduce ad-hoc judgement in the f_g selection process available under

previous code

„ Reduced maximum value of f_g 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 f_g

„ Can also allow for the benefits arising from the design of a redundant

foundation system. Single piles are not redundant and now attract a

Design Geotechnical Strength

„ Design geotechnical strength (R_d,g) is calculated as the design ultimate

geotechnical strength (R_d,ug) multiplied by a geotechnical strength reduction factor (

f

R

f

R

f

_g,

= f

_g,b

+ (f

_t,f

– f

_g,b

).K

f

_g,b

where f

= basic geotechnical strength reduction factor

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

Basic Geotechnical Strength Reduction

Factor f

„ The value of f_g,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 Factors

„ Design Factors „ Installation Factors

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

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

Basic Risk Factors (continued)

TABLE 4.3.2 (A) (cont.)

Risk Category

Risk Factor Weighting factor Design _{Experience with similar}

foundations & conditions 1

Methods of assessing design

parameters for design 2

Design Method Adopted 1

Methods of utilizing in-situ test

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)

Average Risk Rating

„ ARR = S (w_i. IRR_i )/ S w_i

„ Where w_i = weighting factor for the individual risk factor considered „ IRR = 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.

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

Sample Average Risk Rating Calculation

Risk Factor (wi) IRR Wi . IRR

Geological Site Complexity 2 3 6

Extent of Site Investigation 2 4 8

Amount & Quality of Geotech Data 2 4 8 Experience with similar foundations 1 2 2

Method of Parameter assessment 2 3 6

Design Method Adopted 1 3 3

Method of using Insitu/Install data 2 3 6

Level of Construction Control 2 3 6

Level of Performance Monitoring 1 4 4

Sums 15 49

Selection of basic geotechnical strength

reduction factor f

ARR<= 1.5 _{Very low 0.67 0.76}

1.5<ARR<2.0 _{Very low-low 0.61 0.70}

2.0<ARR<2.5 _{Low 0.56 0.64}

2.5<ARR<3.0 _{Low – mod 0.52 0.60}

3.0<ARR<3.5 _{Moderate 0.48 0.56}

3.5<ARR<4.0 _{Mod –High 0.45 0.53}

Geotechnical reduction factor - Benefit of

pile load testing

f

_g

=

f

_g,b

+ (f

_t,f

–

f

_g,b

).K

f

_g,b

where f

= basic factor (0.56 in this example)

f

= intrinsic test factor depends of type of testing

K = testing benefit factor which depends on the

amount of load testing carried out

Intrinsic Test Factor

„

The intrinsic test factor (f

)

is determined by the type

of load testing proposed

„

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)

Testing Benefit Factor K

„ For static, O cell, or rapid load testing

K= 1.33 p / (p + 3.3) <= 1

„ For dynamic load testing

K = 1.13 p /(p + 3.3) <=1

„ where p = percentage of the total number of project piles that are

Testing Benefit Factor

Testing Benefit Factor

0.2 0.4 0.6 0.8 1 1.2 Test ing B e nef it Fact or Static Dynamic

Improvement in f

with percentage of piles tested

Geotechnical Strength Reduction Factor Test Benefit Factor

Static Testing Dynamic Testing

Combined Pile-Raft Foundations

„

Geotechnical Strength Criterion

„

Applies to the group as a whole and is the sum of the

factored strength of the shallow footing f

R

shallow

footing plus f

R

piles

„

Serviceability

„

Requires an analysis which takes into account the

interaction amongst the piles, the raft or shallow footing

and the soil. Usually a 2 or 3D FE analysis.

Negative Skin Friction

„ In the absence of other information, the design ultimate geotechnical

strength shall be assumed to be unaffected by negative friction.

„ Serviceability is often a key design feature and must be considered: „ via a pile-soil interaction analysis (preferred method),

„ or via a requirement for sufficient pile embedment in the “stable

zone” to satisfy strength criteria applied to design load and the negative friction force.

„ R_d,ug,sz f_gs > (E_ds +0.4F_nf)

„ and a serviceability settlement approximated by summing the pile

shaft compression under design load, the shaft compression due to down-drag load and the settlement of the part of the pile in the stable zone under the action of the design load and the negative friction

Section 5 - Structural Design

„ Design Structural Strength is given by: Rd,s = fs k Ru,s

„ fs is taken from the appropriate code for concrete, steel, timber

„ k = concrete placement factor varies from 0.75 to 1.0 as per Table 5.3.2 „ k value depends on pile type, construction methods and the level of

integrity testing and construction monitoring

„ K = 1.0 requires at least 5% integrity testing over full depth of shaft, full

installation monitoring of CFA piles, monitoring of drilling fluid for bored piles, monitoring of drive stresses for precast piles.

„ If integrity testing cannot “see” over the full depth of pile consider using a

Structural Design

„ Precast reinforced concrete piles shall have a longitudinal reinforcement

area of not less than 0.014A_g. This means 350 mm square precast piles require 4 No. 24 mm bars (0.0147), not 4 No. 20 mm bars (0.1026)

„ For other than precast piles, minimum steel area of 0.005 A_g. (as before) „ Partially reinforced piles can have reinforcement curtailed one

development length below the level in the pile when bending and tensile loads cease to be significant and when the design axial load in the

unreinforced section of the pile does not exceed 0.5 k f’_cA_g f_s

„ Unreinforced piles are permitted where the design action effect does not

exceed 0.45 k f’_cA_g f_s

Section 6 - Design for Durability

„ Exposure classification for concrete piles is unaltered

„ Greater reinforcement cover for cast-in-place piles

„ Now have a provision of 50 and 100 year design life cover

„ Steel piles now have separate exposure classifications for water,

refuse fill and soil

Section 7 - Material & Construction Requirements

„ Position. Revised position tolerances now avaiable for piles with deep

cut off levels

„ Non circular piles where axis orientation is specified have10 degree limit „ Installation by jacking

„ Follows Chinese code requirements (inventors of the system) „ Requirements on the installation force to be used

„ P_max =0.74 γ_pR_ug where γ_p is the coefficient of jacking pressure

assessed from static test correlations but not less than 1.4.

„ If no correlations are available take γ_p as 1.5 for piles>15m, 1.75 for 8

m- 15 m and 2.2 for piles < 8m long

„ Repeated jacking required (minimum of 5 repeats)

„ Installation by jacking IS NOT considered to be equivalent to a static

Section 8 - Pile Load Testing

„ Testing benefit factors reward testing with higher f_g factors

„ Where φg,b is 0.4 or less no testing is required unless specified

„ Where φg,b is > 0.4 then testing is mandatory (normative).

„ In absence of tests the verify design ultimate geotechnical strength

tests for serviceability are required for all sites with an ARR > 2.5.

„ Percentage of piles to be serviceability load tested varies with ARR

ARR 2.50 - 2.99 Test 1% of piles

3.00 - 3.49 2%

3.50 - 3.99 3%

4.00 – 4.49 5%

Integrity Testing Table 8.2.4 B

„

Testing of integrity shall be conducted in accordance with

Table 8.2.4(B)

„

Amount of integrity testing (5% to 25%) depends on

Whether the pile design load is governed by pile

geotechnical capacity or pile shaft structural capacity

„

The method of pile construction

„

Construction control and monitoring

„

Integrity test method must be capable of verifying the

integrity of the full length of pile shaft which may preclude

the use of low strain head impact methods for long piles

Determination of Test Load

„

Default test load values for sites without negative skin

friction are nominated

„

Loads for assessment of ultimate geotechnical strength

P

= E

/f

for compression

„

or 1.2 E

for tension or lateral loading

Load for assessment of serviceability

„

P

= E

„

Load for assessment of design geotechnical strength

P

= R

Determination of Test Load

with negative skin friction

„

Maximum test load shall take into account the required

ultimate pile strength in the stable, non down drag zone

„

Test load shall also include allowance for shaft resistance

through settling ground that will provide positive support

during the short duration of the load test but produce long

term negative skin friction

Static Load testing

„

Two types of static load test with procedures are

detailed in Appendix A

„

Proof load test to verify pile compression performance

Load to maximum of P

= E

/f

holding 1hr at P

&

3hrs at P

„

P

= E

plus 2F

for downdrag sites

Total test time ~ 9.5 hrs hr

„

Ultimate geotechnical strength test

„

Load in 10% increments of estimated R

„

Hold for 10 minutes at each increment until gross

Static Load Test Acceptance Criteria

Load Maximum Deflection (mm) P_s= E_ds = design serviceability load P_s L / A E + 0.01d

Ps = E_ds +2F_nf for down drag sites P_s L / A E -0.5 F_nfL_nf/AE + max (0.01d,5)

0 (after removing P_s) Max (0.01d,5) P_g =E_d/φ_g (load for assessment of

design geotechnical strength)

P_gL / A E + 0.05 d 0 (after removing P_u = load for

assessment of ultimate

Dynamic load test acceptance criteria

„ High Strain Dynamic Load Tests with procedures detailed in Appendix B

Load Maximum Deflection (mm) P_s P_s L / AE + 0.01 d

1.5 P_s P_s L/A E + 0.05 d

•

•In the absence of a more detailed analysis, pile head deflections should be taken as the accumulated displacement over all the test blows delivered

Other Pile Test Types

„ Rapid Load Testing (Statnamic) „ Procedures set out in Appendix C

„ Acceptance criteria are as for dynamic load tests

„ Integrity Testing

„ Procedures set out in Appendix D for pulse echo, vibration and impulse

response methods. Cross hole and sonic logging methods are also described with the opportunity to use other test methods if applicable

„ Acceptance criteria are stated in general terms. Tests are deemed

acceptable unless results show a likely impediment of the ability of the pile shaft to perform its intended function

Overall Objectives of Code

„

To improve the standard of pile design and

construction

„

Design is to include a detailed consideration of risk

factors

„

To encourage pile testing by:

„

Recognising design benefits arising from testing

To require load testing in some circumstances

Thank You!!

Questions (?s)

and