A NOVEL APPROACH TO THE PERFORMANCE EVALUATION · PDF fileA NOVEL APPROACH TO THE PERFORMANCE...

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Paper published in 10th

International Conference on Piling and Deep Foundations, 31st May – 2

nd June 06, Amsterdam.

A NOVEL APPROACH TO THE PERFORMANCE EVALUATION OF DRIVEN PRESTRESSED CONCRETE PILES AND BORED CAST-IN-PLACE PILES

Sridhar Krishnan, JOM – JT Joint Venture, Malaysia. ([email protected]) Lee Sieng Kai, Glostrext Technology Sdn Bhd, Malaysia. ([email protected])

This paper presents the results of a comprehensive pre-production pile testing programme for the US$ 800 million 1400MW Coal Fired Jimah Power Plant Project in Negeri Sembilan, Malaysia. The testing programme included high-strain dynamic testing and fully instrumented static axial and lateral load testing of driven prestressed concrete piles and bored cast-in-place piles. A highlight of the testing programme was the pioneering use of the Global Strain Extensometer (GloStrExt) Method, a deformation monitoring system that uses advanced pneumatically- or hydraulically-anchored extensometers and a novel analytical technique to monitor loads and displacements down the shaft and at the toe of driven prestressed concrete piles. The experience with the testing programme for the Jimah Project also demonstrates the possibility of achieving notable breakthroughs, not only in the monitoring, evaluation and reporting of pile foundation behaviour dynamics but also in our understanding of the mechanisms that underpin such behaviour. These significant gains are undeniably a direct result of the committed and co-operative relationship among the project owner, design/builder, specialist piling subcontractors, pile suppliers and pile instrumentation and testing specialists.

INTRODUCTION

The paper’s principal focus is the implementation of a pre-production pile testing programme for the 1400MW Coal-Fired Jimah Power Plant Project in Negeri Sembilan, Malaysia. The testing programme was implemented between October and December 2005 as a lead up to the eventual design and construction of production piles. THE PROJECT Malaysia’s state-owned power utility Tenaga Nasional Berhad has signed a 25-year Power Purchase Agreement with an Independent Power Producer (IPP), Jimah Energy Ventures Sdn. Bhd., to finance, design, build, operate and maintain a 1400MW coal-fired power plant on a 54-hectare intertidal/nearshore site at Jimah in the western Malaysian peninsular state of Negeri Sembilan (Fig. 1). The plant will comprise two units of 700MW each and will be built on a fast-track schedule with the first unit scheduled to be operational in January 2009 and the second unit in July 2009. In September 2004, Jimah Energy Ventures

Sdn Bhd awarded an US$ 800 Million Engineering, Procurement and Construction Contract to a Japanese consortium of Sumitomo Corporation, Toshiba Corporation, Ishikawajima-Harima Heavy Industries Co., Ltd. and Taisei Corporation. The Independent Works, involving construction of an access road, a water supply main and an optical fibre communication line to the power plant site, commenced in January 2005 and is nearing completion at the time of writing. The Reclamation and Soil Improvement Works involving hydraulic sand filling, installation of prefabricated vertical drains and surcharging/preloading commenced in March 2005 and is currently at an advanced stage with preloading in progress at the Coal Yard Area and surcharge removal set to commence shortly at the Power Plant Area. THE SITE The site is located east of the mouth of the Sepang River and off the Kuala Lukut shoreline in the state of Negeri Sembilan in west peninsular Malaysia. It lies at an elevation of between 0m and 5m below the

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Malaysian Land Survey Datum (MLSD, approximate Mean Sea Level). Reference to the geological map of the site and its surroundings (Geological Survey Malaysia, 1985) shows it to be underlain by very soft to soft clays, organic soils and very loose to loose sands presumably deposited during the Pleistocene and Holocene Epochs of the Quaternary Period. The solid geology of the site consists of meta-sedimentary rocks (Phyllite, Schist, Slate and Sandstone) of the Devonian Period. Site Investigations, including boreholes and piezocone tests, later confirmed the geological succession at site as Quaternary deposits overlying a weathered profile of meta-sedimentary rocks (Fig. 2). PRE-PRODUCTION PILE TESTING A comprehensive pre-production pile testing programme, comprising Integrity Testing, High-strain Dynamic Testing and Fully-instrumented Static Axial and Lateral Load Testing of driven prestressed concrete piles and bored cast - in - place piles, was implemented at the Power Plant Area. The specific aims of testing were to: 1. Determine a suitable method for the

installation of 1050mm-diameter bored cast-in-place piles;

2. Investigate the feasibility of using

a) The KODEN Ultrasonic Drilling Monitor to confirm the size, shape and verticality of the drilled hole, and

b) The Pile Integrity Tester (PIT) and Cross-hole Sonic Logging (CSL) to confirm the structural integrity and continuity of the completed pile;

3. Establish suitable driving criteria for the installation of 400mm-, 500mm- and 600mm-diameter prestressed spun concrete piles, based on dynamic monitoring results from the Pile Driving Analyzer (PDA);

4. Investigate the effectiveness of bitumen

slip coating in reducing drag load on prestressed concrete piles through use of a series of instrumented static axial tension tests on coated and uncoated piles;

5. Determine the load-displacement

relationship and distribution of load and displacement along the length of prestressed concrete and bored cast-in-place piles under axial compression and lateral loading; and

6. Determine a site-specific correlation

between high-strain dynamic testing and static load testing of prestressed concrete and bored cast-in-place piles.

Fig. 1: Site Location Plan

Fig. 2: Site Geological Cross-Section

Jimah 1400MWCoal Fired

Power Plant

Jimah 1400MWCoal Fired

Power Plant

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A highlight of the testing programme was the pioneering use of the Global Strain Extensometer (GloStrExt) Method, a deformation monitoring system that uses advanced pneumatically- or hydraulically- anchored extensometers and a novel analytical technique to monitor loads and displacements along the length of driven prestressed concrete piles. The remainder of this paper describes the pile instrumentation schemes with especial emphasis on the GloStrExt Method and presents a selection of the test results obtained using this technique. The pile instrumentation schemes adopted for the pre-production pile testing programme are graphically represented in Figs. 3(a) to 3(c).

THE IMPROVED GLOSTREXT INSTRUMENTATION METHOD FOR DRIVEN PRESTRESSED CONCRETE PILES The Project Owner’s proposal to implement an instrumentation scheme to monitor the performance of driven prestressed concrete piles during static load testing posed the following practical challenges: 1. The fast track nature of the project and the

testing programme made it impractical to incorporate high temperature-resistant strain gauges into the production process of prestressed concrete piles. An additional factor that had to be considered was the high cost of these gauges.

Fig. 3 (a): Instrumentation Details for Static Axial Compression Load Tests

Fig. 3 (b): Instrumentation Details for Static Axial Tension Load Tests

Fig. 3(c): Instrumentation Details for Static Lateral Load Tests

- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - x x x x x

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TP 10

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Legends:

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VW Strain Gauge (4 Nos/Level)

Extensometer Anchored Level

Extensometer VW Sensor

Global Strain Gauge

Pile Joint

Bitumen Slip Coating

GloStrExt Anchored Level

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TP 3C

TP 2

TP 4

Legends:Soil Profile

VW Strain Gauge (2 Nos/Level)


Global Strain Gauge

Jacking System / Load Cell

InclinometersInclinometers

Infilled

Bentonite

Cement

Grout

RL +5.5m

MLSD

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2. Difficulties involved in coordinating the installation of the strain gauges into pile segments and the uncertainty over their ability to withstand the pile production and driving processes.

3. The conventional method of installing either a reinforcement cage with instrumentation attached to the reinforcement bars or a pipe with instrumentation embedded in a cement grout infilling substantially alters the structural properties of the piles, thus rendering them significantly different from the production piles.

The Improved GloStrExt Method was therefore developed to address the above challenges. The method was subsequently applied to the instrumentation of driven prestressed concrete piles TP3C, TP5, TP6, TP7 and TP9 [Fig. 3]. The GloStrExt Method for driven prestressed concrete piles is a state-of-the-art deformation monitoring system using pneumatically- or hydraulically-anchored extensometers coupled with a novel analysis technique for monitoring loads and displacements at various levels along the pile shaft, right down to the toe. The extensometers are installed after the piles are driven, thus enabling engineers to select instrumentation levels along the as-built depth of driven piles using pile driving records and site investigation information as guides. This novel technology that enables installation of instrumentation after pile-driving virtually eliminates the risk of damage of instruments during pile production and installation. The system reliably measures segmental shortening and strains over an entire section of the test pile during each loading step of a typical static pile load test and unlike conventional strain gauges that make just localized strain measurements, integrates the individual measurements thus recorded over a larger and more representative sample. INSTALLATION OF PRE-PRODUCTION PILES The pre-production bored cast-in-place piles TP1 and TP2 were excavated with a Bauer BG25 heavy-duty rotary drilling rig using an 18.5m long temporary casing with bentonite slurry as the stabilizing fluid. The size, shape and verticality of the drilled holes were monitored before concreting using the KODEN DM-604 Ultrasonic Drilling Monitor.

The pre-production prestressed concrete piles TP3C and TP4 were installed with an 11-ton BSP hydraulic impact hammer while piles TP5 through TP10 were installed with a 9-ton Junttan hydraulic impact hammer. Preboring was carried out over the upper 12m for piles TP3C, TP4 and TP5. Dynamic monitoring of piles TP3C, TP4, TP5 and TP9 was carried out during installation using the Pile Driving Analyzer (PDA). The structural properties of pre-production bored cast-in-place and driven prestressed concrete piles are summarized in Tables 1 and 2 respectively. Table 1: Bored Cast-In-Place Pile Properties

Test Pile No.

Pile Diameter

(mm)

Pile Length

(m)

Main Reinfor-cement

Concrete Grade

TP1 1050 47.0 18T25 G40

TP2 1050 49.5 18T25 G40

Table 2: Prestressed Concrete Pile Properties

Test Pile No.

NominalDiameter

(mm)

Wall Thick- ness (mm)

Pile Length

(m)

Pre-stressing

Bar (9mm Ø)

TP3C 600 100 38.9 14 no.

TP4 600 100 38.7 14 no.

TP5 500 90 38.1 10 no.

TP6 500 90 17.5 10 no.

TP7 500 90 17.5 15 no.

TP8 500 90 7.5 10 no.

TP9 400 80 41.7 8 no.

TP10 400 80 17.5 8 no.

REACTION SYSTEMS, LOAD AND MOVEMENT MEASURING SYSTEMS AND TESTING SCHEDULES Typical arrangements for static axial compression, static axial tension and static lateral load tests are shown in Figs. 4(a) to 4(c) respectively. Pile head movement was monitored using both Linear Variation Displacement Transducers (LVDTs) and by affixing pile tops with vertical scale rules that could then be sighted by precise level instruments. Vertical scales were similarly provided on the reference frame to monitor frame movements during load testing. The applied loads were all measured by calibrated vibrating-wire load cells. To ensure close monitoring during the loading and unloading steps, the vibrating-wire

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load cells, strain gauges, GloStrExt sensors and LVDTs were all logged automatically using a Micro-10x datalogger system. Table 3: Testing Schedules

Pile No.

Date Installed

Date of Testing

Total Testing Duration

TP1 27/10/05 09/11/05 to 16/11/05

159 hours

TP2 -TP1

21/10/05 25/11/05 to 27/11/05

33 hours

TP3C 28/10/05 17/11/05 to 23/11/05

122 hours

TP4 -TP3C

17/10/05 01/12/05 to 02/12/05

28 hours

TP5 31/10/05 29/11/05 to 04/12/05

111 hours

TP6 29/10/05 19/11/05 6 hours

TP7 29/10/05 24/11/05 9 hours

TP8 29/10/05 20/11/05 5 hours

TP9 19/10/05 15/11/05 to 21/11/05

132 hours

TP10 28/10/05 23/11/05 6 hours

RESULTS OF THE TESTING PROGRAMME Static axial compression load testing of piles TP1, TP3C, TP5, TP9 & TP10 The measured pile head load-settlement behaviours and the measured pile head load-total shortening behaviours are presented in Figs. 5 and 6 respectively. Highly accurate measurements of the relative deformations of anchored segments across entire pile lengths are now possible, thanks to a new generation of high-precision spring-loaded vibrating-wire sensors (Geokon, 2003) used during load testing.

Fig. 4 (a): Typical Static Axial Compression Load Test Setup

Fig. 4 (b): Typical Static Axial Tension Load Test Setup

Fig. 4 (c): Typical Static Lateral Load Test Setup

Fig. 5: Pile Head Load versus Settlement for TP1, TP3C, TP5, TP9 and TP10

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3000

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7000

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Pile Head Settlement (mm)

Pil

e H

ea

d L

oad

(k

N )

TP3C

`

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oad

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Strain-dependent concrete secant moduli (as described by Fellenius, 2001) were used for load transfer analyses at all strain gauge levels. The load distribution curves acquired from the instrumentation of pre-production piles TP1, TP3C, TP5 and TP9 are presented in Fig. 7. Static axial tension load testing of piles TP6, TP7 & TP8 A purpose-built reaction system [Fig. 4(b)] designed to provide a well-controlled uniformly concentric axial tension load, was used to perform static axial tension load tests on pre-production prestressed concrete piles TP6, TP7 and TP8.

The measured pile head load-upward displacement behaviours are presented in Fig. 8. The structural elongation of the entire length of piles TP6 and TP7, derived from the measurements made by the improved GloStrExt sensors, are presented in Fig. 9. The measured pile head load versus pile toe upward displacement behaviours (derived by subtracting the structural elongation from the pile head upward displacement) are presented in Fig. 10.

Fig. 7: Load Distribution Curves for TP1, TP3C, TP5 and TP9

Fig. 6: Pile Head Load versus Total Shortening for TP1, TP3C, TP5 and TP9

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e H

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Pile Head Upward Displacement (mm)P

ile H

ea

d P

ull-O

ut

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) TP7

TP6

TP8

Fig. 8: Pile Head Pull-out Load versus Upward Displacement for TP6, TP7 and TP8

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Total Structural Elongation (mm)

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Fig. 9: Pile Head Pull-out Load versus Total Structural Elongation for TP6 and TP7

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The ability of the improved GloStrExt Method to yield consistent and reproducible measurements of shortening/elongation and strain throughout testing is fundamentally based on its ability to make these measurements independent of any external reference. This is clearly illustrated in Fig. 11 where a consistent and repeatable accuracy of better than 0.01 mm was achieved in the measurement of segmental movements of pile TP6 during static load testing. To our knowledge, no other approach matches the ability of the GloStrExt technology in achieving this degree of consistency and repeatability in measurements.

Tensile stress-strain curves, modulus-strain curves and load distribution curves acquired from the GloStrExt instrumentation of pre-production piles TP6 and TP7 are presented in Fig. 12. Static lateral load testing of piles TP1/TP2 and TP3C/TP4 The measured pile head lateral load-lateral deflection behaviours for pre-production bored cast-in-place piles TP1/TP2 and prestressed concrete piles TP3C/TP4, derived from both LVDTs and inclinometers, are presented in Fig. 13.

Fig. 11: Pile Head Pull-out Load versus Structural Elongation for Each Anchored Segment of TP6

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d P

ull

-ou

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oa

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) TP6 : From 1.5m to 2.5m depth

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Fig. 12: Tensile Stress-Strain Curves, Modulus -Strain Curves and Load Distribution Curves for TP6 and TP7

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Pile Toe Upward Displacement (mm)

Pile H

ead

Pu

ll-O

ut

Lo

ad

(kN

)TP7

TP6

Fig. 10: Pile Head Pull-out Load versus Pile Toe Upward Displacement for TP6 and TP7

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1000

0 5 10 15 20 25 30 35 40Pile Head (RL+1.45m) Lateral

Deflection (mm)

Pil

e H

ea

d L

ate

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oad

(k

N ) TP1

From LVDTs

From Inclinometers

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Pile Head (RL +1.45m) Lateral

Deflection (mm)

Pile

He

ad

La

tera

l L

oa

d (

kN

)

From LVDTs

From Inclinometers

TP2

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0 20 40 60 80 100

Pile Head (RL +1.9) Lateral Deflection (mm)

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e H

ea

d L

ate

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Lo

ad

(k

N ) TP3C

From LVDTs

From Inclinometers

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Deflection (mm)

Pil

e H

ea

d L

ate

ral L

oa

d (

kN

) TP4

From Inclinometers

From LVDTs

Load dropped drasticly while deflection continued to increase. Pile seemed had been cracked

Fig. 13: Pile Head Lateral Load-Lateral Deflection Curves for TP1/TP2 and TP3C/TP4

0

2

4

6

8

10

12

0 300 600 900 1200 1500 1800 2100

Axial Tensile Strain (x 10-6

)

Pile

He

ad

Str

es

s (

N/m

m2 )

TP6

TP7

0

10

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30

40

50

60

0 300 600 900 1200 1500 1800 2100

Axial Tensile Strain (x 10-6

)

Pile

Se

ca

nt

Mo

du

lus (

kN

/mm

2)

TP6

TP7

0

5

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20

0 200 400 600 800

Loads ( kN)

De

pth

belo

w p

latf

orm

le

ve

l (m

)

TP6

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Loads ( kN)

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elo

w p

latf

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le

vel

(m)

TP7

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Lateral deflection profiles derived from paired inclinometer readings of pre-production bored cast-in-place and prestressed concrete piles are presented in Figs. 14 and 15 respectively. Evaluation of results of instrumentation of concrete piles subjected to lateral loading is often difficult because of the non-elastic nature of concrete and the variable flexural rigidity of concrete piles at high pile loads. However, through careful installation of paired strain gauges attached to reinforcement bars aligned in the direction of loading, bending moment profiles can be quite accurately determined from measured bending stresses, particularly at low loading stages (assuming an elastic section analysis). A representative example is the bending moment profiles of the pre-production bored cast-in-place pile TP2 during lateral load testing (Fig. 16). Additionally, instrumentation with paired strain gauges enables a closer study of the tensile and compressive stresses in a pile under lateral loading (Fig. 17, pile TP2) and permits

examination of the widely-held assumption that cracking in concrete begins when subjected to a tensile stress of around one-tenth its characteristic strength. SUMMARY AND CONCLUSIONS The pre-production pile testing programme for the 1400MW Coal Fired Jimah Power Plant Project has clearly demonstrated that the novel and improved GloStrExt instrumentation method provides high quality, reliable and consistent results. Three features of this method would especially appeal to engineers:

Fig. 14: Measured Lateral Deflection Profiles (3

rd Cycle) for TP1/TP2

RL1.45m

TP3C TP4

0

10

20

30

40

-5 25 55 85 115

DEFLECTION (mm)

DE

PT

H (

m)

Load=0kN

Load=78kN

Load=151kN

Load=174kN

0

10

20

30

40

-515355575

DEFLECTION (mm)

DE

PT

H (

m)

Load=0kN

Load=78kN

Load=151kN

Load=174kN

Fig. 15: Measured Lateral Deflection Profiles (3

rd Cycle) for TP3C/TP4

Fig. 16: Bending Moment Profiles for TP2

Fig. 17: Tensile and Compressive Stresses in TP2 under Lateral Loading

TP2

0

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30

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40

45

50

0 400 800 1200 1600

Bending Moment (kNm)

Dep

th (

m)

L= 157kN

L= 298kN

L= 448kN

L= 600kN

L= 773kN

0mRL+1.45m

Load = L

2m

4m

6m

8m

10m

TP2

0

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0 5 10 15 20

Compressive Stresses

(N/mm2) in Concrete

Dep

th (

m)

L= 157kN

L= 298kN

L= 448kN

L= 600kN

L= 773kN

0

5

10

15

20

25

30

35

40

45

50

-320 -240 -160 -80 0

Tensile Stresses (N/mm2)

Development in Steel

Dep

th (

m)

L= 157kN

L= 298kN

L= 448kN

L= 600kN

L= 773kN

0.0mRL +1.45mLoad = L

RL1.45m

TP1TP2

0

10

20

30

40

50

-5 15 35 55 75

DEFLECTION (mm)

DE

PT

H (

m)

Load=0kN

Load=157kN

Load=298kN

Load=448kN

Load=600kN

Load=773kN

0

10

20

30

40

50

-515355575DEFLECTION (mm)

DE

PT

H (

m)

Load=0kN

Load=157kN

Load=298kN

Load=448kN

Load=600kN

Load=773kN

9




1. The method enables installation of instrumentation after pile-driving and thus virtually eliminates the risk of instrument damage during pile production and installation.

2. The post-install nature of the method

enables engineers to select instrumentation levels along the as-built depth of driven piles using pile driving records and site investigation data as guides.

3. The method reliably measures segmental

shortening/elongation and strains over an entire section of the test pile during each loading step of a typical static load test and unlike conventional strain gauges that make just localized strain measurements, integrates individual measurements over a larger and more representative sample.

Clearly, the GloStrExt Method has tremendous potential as a reliable and powerful pile load testing and data interpretation tool. The authors sincerely hope that the information presented helps persuade engineers to fully examine the method and harness its remarkable potential. Acknowledgement

The authors wish to thank Jimah Energy Ventures Sdn Bhd for permission to publish this paper and bring this important project to a wider audience. The authors also wish to thank Taisei Corporation and their respective organizations for their support References: Geological Survey Malaysia 1985. Geological Map of Peninsular Malaysia 8

th Edition.

Geokon Inc. 2003. Instruction Manual, Model A-9 Retrievable Extensometer. Fellenius, B. H. 2001. From strain measurements to load in an instrumented pile. Geotechnical News Magazine, Vol.19, No.1, pp 35-38.

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