Osterberg cell load test

1. The Osterberg Cell Static
Loading Test
Utilizing The Osterberg Cell for Loading test instead of Conventional
Static LoadingTest
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2. 1. Introduction
• The Osterberg Cell is a Sacrificial jack-like device which the Engineer can have
installed at the tip of a driven pile or on the reinforcement of a bored pile.
• The cell provides the static loading and requires no overhead frame or other
external reaction system.
• Hence, We can now statically test full-sized bored piles (also known as drilled
shafts, drilled piers or caissons) to near their ultimate capacity. Furthermore, we
can do it more conveniently, economically and safely than ever before as no
reaction system required like before.
• O Cell testing and bored pile have a beneficial, cooperative relationship or a
“Symbiosis”.
• Generally high capacity of bored piles, in combination with high cost of top load
system providing more than 10 MN, make conventional top load testing
impractical for routine testing.
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3. 1. Introduction
• The O Cell static load test method, providing high capacities at affordable costs,
has become an attractive alternative method for testing bored piles.
• At mid 1994 the U.S Federal Highway Administration (FHWA) found that
Engineers and Contractors considered the O Cell “the method of choice” and it’s
use had risen rapidly to about 65% of all bored pile testing, this trend has
continued and usage now exceed 90% not in the U.S only but all over the world.
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4. 1. Introduction
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Osterberg
Cell

5. 2. Static load testing using O Cell
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Fig.
1
Pile
Steel Beam
P=F+Q
F
Q
Pile
F
Q
Expanding
O Cell at the
bottom of
the pile
Ground Level
Ground Level
Reaction System
at the top of pile
Q

6. 2. Static load testing using O Cell
• A Conventional test loads the bored pile in compression, at its tip, using an
overhead reaction system or dead load, side shear F and end bearing Q combine
to resist the top load P and Engineer can only separate this components
approximately by analysis of strain and compression measurements together
with modulus estimates.
• The O Cell also loads the pile in compression, but from its bottom. As the O Cell
expands, the end bearing Q provides reaction for the side shear F. and vice versa.
Until reaching the capacity of one of the two component or the O Cell reaches its
capacity. The vantage point here is that the test separate the side shear and end
bearing components.
• The O Cell test load placed at, or near, the bottom of the pile has twice testing
effectiveness of that same load placed at the top in a conventional test.
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7. 12/12/2016 Alaa Mohamed Metwally
3. Equipment
7

8. 3. Equipment
• After construction of the shaft, the test operator connects an automatic pump to
the hydraulic lines that provides a pressure conduit to the cell, the load applied
by an O Cell is calibrated versus hydraulic pressure before installation and the
pressure applied to the cell is measured by a pressure transducer.
• Movement measured by electronic gages connected to a computerized
acquisition system.
• The total expansion of the cell is measured by (LVWDTs) Linear vibrating wire
transducers the lower part of which attached to bottom of the cell.
• A steel telltales attached to the bottom of the cell used to measure the upward
movement directly.
• Subtracting the upward movement from total expansion gives the desired
downward movement.
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10. 4. History of Osterberg Cell
• Dr. Jorje Osterberg, professor emeritus at Northwestern university. Developed
and patented test which now carries his name.
• The first experimental test pile was carried out in 1984, after this successful
prototype professorOsterberg works very closely to American Equipment and
Fabrication Corp. to evolve his cell from a bellows type expansion cell to the
current design, very similar to piston type jack used in conventional test, but the
piston extends downward not upward.
• Haley & Aldrich was the first to use O Cell in practical application in 1987, to
driven piles one over a river in Massachusetts and the other on a bridge which
reaches 1.26 and 4 MN respectively.
• Now Osterberg cell has steadily gained popularity all over the world for testing
bored piles.
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11. 5. Advantages of O Cell
• Economy.
• reduced construction time, saving in outlay capital, no top-of-pile reaction equipment required
and less test design efforts, making the test cost from
1
3
to
2
3
the conventional test.The
comparative cost reduces as the load increases.
• High Load capacity.
• Shear/Bearing Component
• The cell automatically separates the side shear and end bearing components, despite of
conventional test which gives the total capacity at a time
• Improved safety.
• The test energy lies deeply buried and no overhead load at the top of pile.
• Rocket Socket.
• The cell loaded at the bottom of the socket, near its bottom and gives an automated separation
of components
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12. 5. Advantages of O Cell
• Reduced work area.
• A 65 MN O Cell test, conducted in a 3 meter wide median strip of a busy interstate highway,
which seems impossible when using conventional test as a big area needed for the reaction
system or equipment and kentledge system.
• Over water and battered shafts.
• Static creep and setup effects.
• Because the test is static the test load at any length of time can be estimated, the Engineers
also can obtain separate data about creep behavior for the two components.
• Sequential testing.
• A long term stage tests with minimal efforts can be made for research purposes or other to
obtain “aging” for example, been a unique advantage of O Cell test
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13. 6. Limitations
• Advance installation required.
• In bored piles and most driven piles, the O Cell must be installed prior construction.
• Balanced component requirement.
• As the cell reaches the ultimate capacity in only one of its components, and shaft capacity limited
to two times the capacity of component reaching ultimate, The Engineer should first analyze the
expected side shear and end bearing components and either attempt to balance the two to get
the most information from both.
• The introduction of multilevel cell mitigates this limitation, and allow calculating ultimate side
shear and end bearing in cases where bearing less than the side shear.
• Equivalent top load curve.
• Although the estimation of equivalent top load curve is conservatism, it remains estimate.
• Sacrificial cell.
• Cell considered expandable and not recovered after the test completed. However, grouting the
tested pile allows using it as a permanent foundation pile.
• Not suitable for certain types of piles.
• H pile and sheet piles.
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14. 7. Test results
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Sand and
gravel
shell
8.2
19.2
5.8
2.4
River
18.9
Hydraulic
supply &
telltale casing
35.7 -25
-20
-15
-10
-5
0
5
10
15
20
0 10 20 30
UpwordandDownwordMovement
(mm)
Load (MN)
Osterberg Load-Movement Curve
Purpose: To determine bearing capacity of the drilled shaft supporting a
bridge pier.
Method: Shafts drilled with polymer drilling slurry, 1.9 O.D. casing set on
top of shale and 1.8 m hole drilled 5.8 m into shale 864mm load cell with 1.7
m diameter plate welded to bottom lowered into the hole. Pumped
concrete placed to design top elevation of shaft.
Results: Load reaches capacity of device at 34.56 mm downward and 7.62
mm upward movement, the ultimate capacity was greater than 54 MN.
O-CellTest on a rock socketed bored
pile

15. -25
-20
-15
-10
-5
0
5
10
15
20
0 5 10 15 20 25 30
UpwordandDownwordMovement(mm)
Load (MN)
Osterberg Load-Movement Curve
8. Interpretation of test results.
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-18
-16
-14
-12
-10
-8
-6
-4
-2
0
0 10 20 30 40 50 60
Movement(mm)
Load (MN)
Equivalent Top Load-Movement Curve

16. 8. Interpretation of test results.
• The Osterberg cell loads the test pile in compression similar to a conventional
top load test, and hence the data form o cell is analyzed in much the same way
of conventional test.
• The only significant difference between the two tests is that the o cell provides
two load-movement curves, one for side shear and one for end bearing.
• Combined bearing capacity of the two components obtained as follow:
• Select an arbitrary point on the load movement curve, and determine the side shear.
• Determine the end bearing for the same point.
• From the upper two value we construct a point on “Top Load-Movement curve”.
• Repeat the process for multiple points and construct the curve.
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17. 9. References
1. John H.Shmertmann & johnA. Hayes “The Osterberg cell and bored pile
testing- a symbiosis".TheThird International Geotechnical Engineering
Conference-Cairo University, 5-8 Jan 1997.
2. https://www.youtube.com/watch?v=fDJVpe37_Qg
3. https://www.youtube.com/watch?v=afKrgdJf2k4&spfreload=10
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18. Presented By
Student at Nile Academy for Science and Technology
Code: 130326
Due date: 9-12-2016
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