1 Presented by : Lee Sieng Kai Glostrext Technology (S) Pte Ltd www.glostrext.com.my Recent Development in Pile Instrumentation Technology for Driven, Jacked-in and Bored Cast-in-place Piles Date : 20 August 2010 Venue : Engineering Auditorium, National University of Singapore GEOTECHNICAL SEMINAR GEOTECHNICAL SEMINAR GEOTECHNICAL SEMINAR GEOTECHNICAL SEMINAR JOINTLY ORGANIZED BETWEEN GEOTECHNICAL SOCIETY OF SINGAPORE (GEOSS) & CENTRE FOR SOFT GROUND ENGINEERING • Introduction • The need and trends in pile instrumentation • Review of Conventional Methods • Conventional pile instrumentation method for bored piles • Conventional and Approximate methods for precast piles • Development of Global Strain Extensometer Technology • Review of basic deformation measurement in pile by strain gauges and extensometers • Case Histories • Application on precast piles • Application on bored piles • Illustration of Instrumented Test Piles using Global Strain Extensometer Technique • Discussion and Concluding Remarks • The benefits of using the Global Strain Extensometer technology Outline
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Recent Development in Pile Instrumentation Technology for Driven, Jacked-in and Bored Cast-in-place Piles
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1
Presented by : Lee Sieng Kai Glostrext Technology (S) Pte Ltd
www.glostrext.com.my
Recent Development in Pile Instrumentation Technology for Driven, Jacked-in and
Bored Cast-in-place Piles
Date : 20 August 2010
Venue : Engineering Auditorium, National University of Singapore
JOINTLY ORGANIZED BETWEEN GEOTECHNICAL SOCIETY OF SINGAPORE (GEOSS)
& CENTRE FOR SOFT GROUND ENGINEERING
• Introduction• The need and trends in pile instrumentation
• Review of Conventional Methods• Conventional pile instrumentation method for bored piles
• Conventional and Approximate methods for precast piles
• Development of Global Strain Extensometer Technology• Review of basic deformation measurement in pile by strain gauges and
extensometers
• Case Histories• Application on precast piles
• Application on bored piles
• Illustration of Instrumented Test Piles using Global Strain Extensometer Technique
• Discussion and Concluding Remarks• The benefits of using the Global Strain Extensometer technology
Outline
2
Introduction : basic static load test methods
Four basic pile load test methods (Joshi and Sharma, 1987)
1. Slow Maintained Load Test Method (SM Test or SMLT)
2. Quick Maintained Load Test Method (QM Test or QMLT)
3. Constant Rate of Penetration Test Method (CRP Test)
4. Swedish Cyclic Test Method (SC Test)
Main construction control for piles in early years:• Based on the measurement of set of each pile (driven); and
• A selected small number of non-instrumented static load tests to verify the Capacity and specified Load- Settlement requirement.
Introduction : basic static load test methods
Comparison of required time for various test methods (Fellenius, 1975)
Comparison of load-movement behavior for test methods (Fellenius, 1975)
3
2800t
2400t 4200t
2400t
Introduction : Examples of reaction load setup for axial compressive load tests on piles
• Millions (or billions?) of dollars are wasted every year due to over-designed (and under-provided!)foundations worldwide !
• There is tremendous needfor the static load test on preliminary test piles to be instrumented to measure and evaluate pile settlement, structural shortening /elongation, bearing capacity and transfer of load from the pile shaft and pile toe to the soil.
Introduction: The Need for Pile Instrumentation
SoftLayer
Competent Soil Strata
Existing GL
10.0 m
20.0 m
30.0 m
0.0 m
Ideal founding depth at 20.0 m
Case 1:
Ideal,
adequate,
safe and
economical
Case 2:
Over-
conservative,
not
economical
Case 3:
Under-
provided,
not safe
4
Introduction : Codes and Design Methods for Foundation Piles
According to Ken Fleming (1996): The basic parameters required for forecasting pile deformation under loads are :
(a) . Ultimate shaft load and its characteristics of transformation to the ground;
(b). Ultimate base load;
(c) . Stiffness of the soil below the pile base;
(d). Pile dimensions; and
(e) . Stiffness of the pile material.
CP4: 2003 7.5.3(b) Empirical correlation with SPT N-values using modified Meyerhof Equation are widely used in this region, where the ultimate bearing capacity of a pile in compression is given by:
Qu = Ks * Ns * As + Kb*(40Nb)*Ab
all the terms in equation as explained in CP4:2003
Circular on revised Singapore Standard on Code of Practice for Foundations CP4: 2003
5
• Sacrificial cast-in instrumentation method for cast-in-place bored piles:
• Vibrating wire strain gauges (recently fiber optic strain gauges) and mechanical tell-tales are normally installed and cast within the pile to allow for monitoring of axial loads and movements along the pile shaft.
• Similarly for grout-in-situ micropiles, barrettes etc..
Review of Conventional Methods : Cast-in-place piles Conventional Instrumented Test Pile
Apllied load measured by vw load cells
Pile head PTop Platform level
Verify and back- calculate Ec
Strain Gauges Lev. A
PB Tell-tale Extensometer 1
Strain Gauges Lev. B
P = ε (Ec Ac + Es As)or
P = ε (Ec Ac) PC follow normal terms
Strain Gauges Lev. C
PD Tell-tale Extensometer 2
Strain Gauges Lev. D
PE
Strain Gauges Lev. E
PF
Strain Gauges Lev. F Tell-tale Extensometer 3
Pile toe
Legend:
denotes Vibrating Wire Strain Gauges
denotes mechanical tell-tale extensometer
Review of Conventional Methods : Cast-in-place piles
• Some discussions/concerns on sacrificial cast-in instrumentation method for cast-in-place piles: • Generally this is the most commonly adopted method, most
engineers are familiar with it, and it yields satisfactory results for estimate of shaft & base resistances
• However, very often when there is difficulty in pile installation (concreting time, hole collapse……) or due to human problem, the instruments also get damaged! and that is the time…
Review of Conventional Methods: Precast concrete piles
For precast driven / jack-in piles, the application of instrumented full-scale static load tests is far more challenging than their bored pile counterparts due to significant difference in method of pile installation.
Due to practical shortcoming of conventional instrumentation method and the lack of innovation in this area, instrumented full-scale static load tests are in fact rarely used in driven pile application in this region.
Therefore, the far lacking driven pile industry is long due for a better technology to revolutionize the methodology in the acquisition of design data in a more accurate and reliable way, to catch up with the evolution in the design methods.
Conventional Instrumentation Method for Prestressed Spun Concrete Piles
•Conventional instrumentation method for spun concrete piles piles:
• By incorporating high temperature-resistant strain gauges into the autoclaved heat-cured “spin-cast” production process of prestressed spun concrete piles
Strain Gauges Lev. A
Strain Gauges Lev. B
Strain Gauges Lev. C
Strain Gauges Lev. D
Strain Gauges Lev. E
Strain Gauges Lev. F
Existing Ground Level
Legends:
denotes high temperature - resistant
Strain Gauges
denotes Pile Joint
0
5
10
15
20
25
30
0 50 100 150N (blows/30cm)
Depth (m)
Clay
Sandy
Clay
Sandy
Silt
Spun Pile
Hollow annular space
Pile toe at 30.0 m depth
SI borehole log
(Pile head)
7
This method is extremely unpopular and difficult to be routinely applied in project sites due to the following constraints:
(a) High cost of these temperature-resistant strain gauges;
(b) Tremendous difficulties involved in coordinating the installation of the strain gauges into pile segments;
(c) Long lead-time is normally required for instrumentation works, as the instruments have to be pre-assembled and installed onto the high strength prestressing bar cage prior to autoclaved heat-cured ‘spin-cast’ production process of the piles; and
(d) Great uncertainty over the ability of the delicate instruments to withstand the stresses arising from pile production and driving processes.
Constraints of Conventional Method
• Due to the difficulties of using the conventional method, the engineering community for spun pile industry has been using an approximate instrumentation method for the past few decades, by installing either an instrumented reinforcement steel cage or an instrumented pipe, into the hollow core of spun piles followed by cement grout infilling
Strain GaugesvLev. A
Strain Gauges Lev. B
Strain Gauges Lev. C
Strain Gauges Lev. D
Strain Gauges Lev. E
Strain Gauges Lev. F
Existing Ground Level
Legends:
denotes Vibrating Wire Strain Gauges
denotes Pile Joint
Spun Pile
Cement Grout
Instrumented Pipe
0
5
10
15
20
25
30
0 50 100 150N (blows/30cm)
Depth (m)
Clay
Sandy
Clay
Sandy
Silt
Pile toe at 30.0 m depth
SI borehole log
(Pile head)
Approximate Instrumentation Method for Prestressed Spun Concrete Piles
8
Typical installation process of spun pile instrumentation in Approximate Method
Approximate Instrumentation Method for Prestressed Spun Concrete Piles
(i) (ii)
(iii) (iv)
Cement Grout Infill (Usually Grade 25)
Original
Wall
Thickness
(usually
Grade 80
Concrete
Instrumented Pipe (Instrumented Cage also
commonly used)
Section of instrumented spun pile after cement grout infilling in Approximate Method
Approximate Instrumentation Method for Prestressed Spun Concrete Piles
9
The obvious shortcomings of this approximate method include:
(a) The infilling of cement grout substantially alters the structural properties of the piles, thus rendering them significantly different from the actual working spun piles, which are usually not grouted internally;
(b) The change in strain in the post-grouted core under the applied loading may not be the same as the change in strain in the prestressed concrete wall of the pile because of the different stiffness of the two materials of different mix, strength and age;
(c) Structural shortening measurement of the test piles are not representative of the actual working piles;
(d) Structural integrity of the original pile cannot be reliably ascertained, particularly performance of pile joints, during the static load test; and
(e) Significant time loss due to grout infilling and curing process, beside the environmental unfriendly nature of this method.
Shortcomings of Approximate Method
Glostrext inside
Arrangement of Global Strain Extensometer instrumentation approach for typical spun pile instrumentation application
50mm dia. Hole
Opening (Bottom
Plate) & 25mm Trench (Top Plate)
Min. 50mm thk Steel Plate
Min. 50mm thk pile top
steel plate (with 50mm
dia. centre hole)
Glostrext Anchor
Glostrext Sensor
Connecting Rod,
Hose & Signal Cable
Jacking System with Load Cell
12.5mm thk
Plywood
To Datalogger
Datalogger
Glostrext Sensor
Signal Cables, pressure hole
Min. 50mm thk Top
Steel Plate
Min. 50mm thk
Bottom Steel Plate
Development of Global Strain Extensometer Technology
Major breakthrough : Significant difference in the methodology adopted, from sacrificial cast-in method used in conventional technologies to a novel post-install approach
10
Glostrext inside
Completed improved prototype for application
Development of Global Strain Extensometer Technology
Glostrext inside
Actual Global Strain Extensometer system for spun pile application
Development of Global Strain Extensometer Technology
11
Glostrext inside
Laboratory Verification Tests
Development of Global Strain Extensometer Technology
1200 mm
VWSGs Lev A: A1, A2, A3, A4
615 mm (Global Strain
Extensometer Sensor inside)
VWSGs Lev B: B1, B2, B3, B4
VWSGs Lev C: C1, C2, C3, C4
Glostrext inside
Development of Global Strain Extensometer Technology
Results and discussion will be published by UM (Prof. Faisal & Lee) at later stage
12
Basic concept
GaugeLength
GaugeLength
Accuracy of 0.1mm at best by DG/LVDT
Accuracy of 0.002mm or better
• Review of basic deformation measurement in pile by strain gauges and extensometers
•From a ‘strain measurement’ point of view, the strain gauge gives strain measurement over a very short gauge length while the extensometer gives strain measurement over a very long gauge length!
•Extensometer that measure strain over a very long gauge length may be viewed as a very large strain gauge or simply called Global Strain Extensometer ���� (Glostrext)
BASIC PRINCIPLE OF MEASUREMENT INVOLVED
Global Strain Extensometer Instrumentation Scheme for Spun Piles
Schematic diagram of typical instrumented spun pile using Global Strain Extensometer technology
Anchored Lev. 6
Anchored Lev. 5
Anchored Lev. 4
Anchored Lev. 3
Anchored Lev. 2
Anchored Lev. 1
Anchored Lev. 0 Global Strain Gauge Lev. A Extensometer Lev. 1
Global Strain Gauge Lev. B
Global Strain Gauge Lev. C
Global Strain Gauge Lev. D
Global Strain Gauge Lev. E
Global Strain Gauge Lev. F
Extensometer Lev. 2
Extensometer Lev. 3
Extensometer Lev. 4
Extensometer Lev. 5
Extensometer Lev. 6
Existing GL
Legends:
denotes Glostrext anchored level
denotes Glostrext Sensor
denotes Pile Joint
Spun PileHollow annular space
Pile toe at 30.0 m depth
Pressure supply,
regulator and manifold
Jacking System
and Reaction
Load Setup
DataloggerData collection
Load transferred (PAve) at mid-point of each anchored interval can be calculated as:
P = ε(Ec Ac )
where,
ε = average change in global strain gauge readings;
Ac = cross-sectional area of spun pile section;
Ec = concrete secant modulus in pile section
13
Global Strain Extensometer Scheme for RC Piles Description of Global Strain Extensometer (Glostrext) Instrumentation Technology for Reinforced Concrete Square Pile Static Load Tests
Instrumented RC Square Pile
Pile top load measured by VW Load Cell.
Anchored Lev. 0 Platform level
(Global Strain Gauge Lev. A)
Anchored Lev. 1 Extensometer Lev. 1
RC square pile
(Global Strain Gauge Lev. B)
Anchored Lev. 2 Extensometer Lev. 2
(Global Strain Gauge Lev. C)
Anchored Lev. 3 Extensometer Lev. 3
(Global Strain Gauge Lev. D)
steel pipe
Anchored Lev. 4 Extensometer Lev. 4
(Global Strain Gauge Lev. E)
Glostrext Sensor
Anchored Lev. 5 Extensometer Lev. 5
Glostrext Anchor (Global Strain Gauge Lev. F)
Anchored Lev. 6 Extensometer Lev. 6
Pile toe
Legend:
denotes Glostrext anchored level
denotes Glostrext Sensor
Global Strain Extensometer Scheme for RC Piles Instrumented Micropile
Global Strain Extensometer Scheme for Bored PilesGlobal Strain Extensometer Method for bored piles
Apllied load measured by vw load cells
Pile head
Instruments: Level No.
Global Strain A 2
Gauge B 2
C 2
D 2
E 2
F 2
Total= 12
Extensometer 1 2
2 2
3 2
4 2
5 2
6 2
Total= 12
Pile toe
Legend:
denotes GLOSTREXT anchored level
denotes GLOSTREXT Sensor
Global Strain Gauge Lev. A
Anchored Lev. 0
Anchored Lev. 1
Anchored Lev. 2
Global Strain Gauge Lev. B
Anchored Lev. 3
Global Strain Gauge Lev. C
Anchored Lev. 4
Global Strain Gauge Lev. D
Global Strain Gauge Lev. E
Global Strain Gauge Lev. F
Anchored Lev. 5
Anchored Lev. 6
Ext. Lev. 1
Ext. Lev. 2
Ext. Lev. 3
Ext. Lev. 4
Ext. Lev. 5
Ext. Lev. 6
Case Histories (Precast/Prestressed piles)
Recommended for reading :
1. Krishnan S. & Lee S.K., 2006. “A Novel Approach to the Performance Evaluation of Driven Prestressed Concrete Piles and Bored Cast-in-place Piles”. Proceedings of 10th International Conference on Piling and Deep Foundations, Amsterdam, pp 718-726
2. S.K. Lee, T.K. Lau, A.H. Tan, Faisal Hj. Ali, Y.W. Chong, 2007. “Recent Development in Pile Instrumentation Technology for Driven and Jacked-in Prestressed Spun Concrete Piles”, Proceedings of 16th South East Asian Geotechnical Conference, Kuala Lumpur, pp. 727-734.
3. Research Jacked-in Piles at Tuas South Avenue 2/5, 2009. CSCG-NUS (not yet published).
15
Applications of GLOSTREXT technology for Marine Piles:
1000mm Ø (with1400mm wall thickness) driven prestressed spun concrete pile GLOSTREXT instrumentation for 23 km long 2nd Penang Bridge, Malaysia, 2008.
Depth (m) Test Pile MLT-C (1000mm Ø)0.0 m RL +4.5m (Pile Head (H))
RL 0.00 m MLSD
Hollow core
Spun pile
Pile toe at 45.3 m depth (RL -40.8m)
Legend:
denotes Glostrext anchored level
denotes Glostrext Sensor
SI Borehole BH-16
45.0 m Anchored Lev. A-6
42.5m
Glostrext Sensor 2
11.5 m
Glostrext Sensor 325.0 m
21.5 m Anchored Lev. A-2
Anchored Lev. A-5
Glostrext Sensor 433.25 m
28.5 m Anchored Lev. A-3
Global Strain Gauge Lev. D
Extensometer Lev. 3
Global Strain Gauge Lev. C
Extensometer Lev. 2
Global Strain Gauge Lev. B
Global Strain Gauge Lev. A
Extensometer Lev. 1
Extensometer Lev. 6
Glostrext Sensor 16.5 m
1.5 m
Anchored Lev. A-1
Anchored Lev. A-0
Extensometer Lev. 5
43.75m Global Strain Gauge Lev. F Glostrext Sensor 6
39.0 m Anchored Lev. A-4 Extensometer Lev. 4
Global Strain Gauge Lev. E40.75m Glostrext Sensor 5
4.5 m
8
6
7
7
8
14
15
18
19
21
27
91
94
64
75
51
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
0 25 50 75 100
SPT value, N
(blows/30cm)
Depth below pile top (m)
Seabed (RL-7.0m)
16.5 m
Seabed (RL-7.0m)
VS-1:
Peak=16kPa
Rem=5kPa
VS-2:
Peak=27kPa
Rem=10kPa
VS-3:
Peak=43kPa
Rem=13kPa
Silty Clay
Silty Sand
Applications of GLOSTREXT technology for Marine Piles:
1000mm Ø (with1400mm wall thickness) driven prestressed spun concrete pile GLOSTREXT instrumentation for 23 km long 2nd Penang Bridge, Malaysia, 2008.
16
Applications of GLOSTREXT technology for Marine Piles:
Glostrext Sensor 425.3 m Global Strain Gauge Lev. D
Global Strain Gauge Lev. C
Extensometer Lev. 2
Global Strain Gauge Lev. B
Extensometer Lev. 7
Glostrext Sensor 28.55 m
3.55 m Anchored Lev. A-1
Extensometer Lev. 6
29.8m Global Strain Gauge Lev. G Glostrext Sensor 7
26.3 m Anchored Lev. A-4 Extensometer Lev. 4
Global Strain Gauge Lev. E27.3m Glostrext Sensor 5
0
0
43
42
100
111.1111111
136.3636364
142.8571429
136.3636364
125
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
0 50 100 150 200 250 300
Depth below pile top (m)
SPT value, N (blows/30cm)
Seabed (RL-9.433m)
Depth (m)
0.0 m
RL 0.00 m CD
RL +3.8m (Pile Head (H))
Global Strain Gauge Lev. A Glostrext Sensor 1
Anchored Lev. A-0
Extensometer Lev. 1
24.3m Anchored Lev. A-3 Extensometer Lev. 3
1.925 m
Hollow core
Spun pile
13.233m
0.3 m
Seabed (RL-9.433m)
VS-1:Peak=14kPa
Rem=4kPa
Marine Clay
VS-2:Peak=23kPa
Rem=8kPa
VS-3:Peak=40kPa
Rem=15kPa
OA
28.3m Anchored Lev. A-5 Extensometer Lev. 5
Global Strain Gauge Lev. F28.8m Glostrext Sensor 6
Applications of GLOSTREXT technology for RC Sq. Piles:
400mm x 400mm driven reinforced concrete square pile GLOSTREXT instrumentation at Damansara, Malaysia.
Instrumented Pile
(RL 40.0mm )
Pile toe at 24.3 m depth
Legend:
denotes Glostrext anchored level
denotes Glostrext Sensor
SI Borehole : BH9
3
5
4
12
11
13
8
12
12
9
12
13
15
12
15
71
79
61
71
79
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
0 50 100 150 200
Depth below original ground level (m)
SPT value, N (blows/30cm)
24.3m Anchored Lev. 6
Glostrext Sensor 24.8m
Glostrext Sensor 311.3 m
8.3 m Anchored Lev. 2
Glostrext Sensor 417.3 m
14.3 m Anchored Lev. 3
Global Strain Gauge Lev. D
Extensometer Lev. 3
Global Strain Gauge Lev. C
Extensometer Lev. 2
Global Strain Gauge Lev. B
Global Strain Gauge Lev. A
Extensometer Lev. 1
Extensometer Lev. 6
Glostrext Sensor 10.8 m
1.3 m
0.3 m
Anchored Lev. 1
Anchored Lev. A-0
23.8m Global Strain Gauge Lev. F Glostrext Sensor6
Glostrext Sensor 521.8 m Global Strain Gauge Lev. E
Extensometer Lev. 4 20.3 m Anchored Lev. 4
52mm Ø i.d.
steel pipe tohouse instruments
RC pile
23.3m Anchored Lev. 5 Extensometer Lev. 5
Clayey Sand
Sand
Sand Silt
Silty Sand
17
Case Histories (Bored Piles)
Recommended for reading :
1. H.M. A. Aziz & S.K. Lee, 2006. Application of Global Strain Extensometer (GLOSTREXT) Method for Instrumented Bored Piles in Malaysia. Proceedings of 10th International Conference on Piling and Deep Foundations, Amsterdam, pp 669-767
Illustration of Test Results for Instrumented Test Pile using Global Strain Extensometer Technique
Application of Global Strain Extensometer Technique for 450mm Ø (with 80mm wall thickness) driven prestressed spun concrete pile for a reclaimed island petrochemical facilities project in Johor , Malaysia, 2008.
Test Pile No.
Nominal Diameter (mm)
Wall Thickness (mm)
9mm Ø Pre-stressing Bar Reinforcement
Driven Pile
Length (m)
Hydraulic Hammer Weight (tons)
Drop Height (mm)
Final Set (mm)
Date Driven
STP3 450 80 8 no. 47.25 9 400 3 21st Apr 08
19
Glostrext inside
Instrumentation levels for Instrumented Test Spun Pile STP3 (450 mm Ø) (with 80mm wall thickness)
Driven Pile length = 47.25m from Platform Level of RL 6.18 mCD
Instrumented Spun Pile
(RL 6.18m CD)
hollow core
spun pile
Bitumen coated
Pile toe at 47.25 m depth
Legend:
denotes Glostrext anchored level
denotes Glostrext Sensor
SI Borehole : BH-STP3
9
12
14
16
18
11
8
2
0
2
3
4
10
13
15
9
15
16
19
22
26
27
20
25
22
25
18
17
19
16
19
25
30
136
167
273
250
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
0 50 100 150 200 250 300
Depth below original ground level (m)
SPT value, N (blows/30cm)
47.2m Anchored Lev. 10
46.2m
Glostrext Sensor 24.7m
Glostrext Sensor 422.2 m
20.2 m Anchored Lev. 3
Anchored Lev. 9
Glostrext Sensor 526.45 m
24.2 m Anchored Lev. 4
Global Strain Gauge Lev. E
Extensometer Lev. 4
Global Strain Gauge Lev. D
Extensometer Lev. 3
Global Strain Gauge Lev. B
Global Strain Gauge Lev. A Extensometer Lev. 1
Extensometer Lev. 10
Glostrext Sensor 10.7 m1.2 m
0.2 m
Anchored Lev. 1
Anchored Lev. A-0
46.7m Global Strain Gauge Lev. J Glostrext Sensor 10
Extensometer Lev. 9
Glostrext Sensor 737.7 m Global Strain Gauge Lev. G
Extensometer Lev. 5 28.7 m Anchored Lev. 5
8.2 m Anchored Lev. 2 Extensometer Lev. 2
Glostrext Sensor 314.2 m Global Strain Gauge Lev. C
Sand fill
Soft Marine Clay
VS-3:Peak=52kPa
VS-4:Peak=39kPa
VS-2:Peak=39kPa
VS-1:Peak=39kPa
VS-5:Peak=59kPa
VS-6:Peak=77kPa
Clayey Sand
Silty Sand
Rock
Silt
Glostrext Sensor 631.95 m Global Strain Gauge Lev. F
Extensometer Lev. 6 35.2 m Anchored Lev. 6
Extensometer Lev. 7 40.2 m Anchored Lev. 7
Glostrext Sensor 842.2 m Global Strain Gauge Lev. H
Extensometer Lev. 8 44.2 m Anchored Lev. 8
Glostrext Sensor 945.2 mGlobal Strain Gauge Lev. I
Instrumentation and maintained pile load test
Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of pile top load versus pile top settlement, pile base settlement and total shortening for 450mm Ø Test Pile STP3
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
0 5 10 15 20 25 30 35 40 45 50 55 60
Pile Top Load (kN )
Pile Top Settlement /Pile Base Settlement / Total Shortening (mm)
Pile Top Settlement Pile Base Settlement Total Shortening
20
Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of pile top load versus pile shortening for various segments for 450mm Ø Test Pile STP3
Piletop Settlement Sett at 1.2m Sett at 8.2m Sett at 20.2m
Sett at 24.2m Sett at 28.7m Sett at 35.2m Sett at 40.2m
Sett at 44.2m Sett at 46.2m Sett at 47.2m
`
21
Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of back-calculated Concrete Modulus values, Ec, versus Measured Axial Strain at Level A using Global Strain Extensometer technique for 450mm Ø test pile STP3
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Load Transfer Characteristics during Loading stages for 450mm Ø test pile STP3
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Mobilised Unit Shaft Friction ( kN/m
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Average Movement of Pile between soil stratum ( mm )
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Lev B to Lev C
Lev C to Lev E
Lev E to Lev G
Lev G to Lev H
Lev H to Lev I
Lev I to Lev J
Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of Mobilised Unit End Bearing versus Pile Base Settlement for 450mm Ø test pile STP3
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Mobilised Unit End Bearing ( kN/m
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Pile Base Settlement ( mm )
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Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of Applied Pile Top Load, Total Shaft Resistance and Base Resistance versus Pile Top Settlement for 450mm Ø test pile STP3
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Load ( kN )
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Glostrext inside
Illustration of Test Results for Instrumented Spun Pile using Global Strain Extensometer Technique
Plot of Pile Base Load over Applied Pile Top Load versus Pile Top Settlement for 450mm Ø test pile STP3
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Pb/Ptop ( % )
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Discussion and Concluding Remarks
Technology novelty and advantages
Global Strain Extensometer Technology
Costs
User Value
Value Innovation
Obvious COSTS benefits :
i) Significant cost/time saving;
ii) Environmental friendly (no grouting needed);
iii) Eliminates instrument damage risk.
Obvious VALUE benefits :
i) Flexibility to select instrumentation levels after pile installation;
ii) Reliable measurements over a larger and more representative sample;
iii) Routine instrumentation made viable
Discussion and Concluding Remarks
In summary, three distinct features of this method would especially appeal to geotechnical engineers:
(i) the method enables installation of instrumentation after pile installation and thus virtually eliminates the risk of instrument damage during pile production and installation;
(ii) the post-install nature of the method enables engineers to select instrumentation levels along the as-built depth of piles using pile installation records and site investigation data as guides;
(iii)the method reliably measures segmental shortening 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 which only provide localized strain measurements, it integrates individual strain measurements over a larger and more representative sample, thus making the test results more informative.