The osterberg cell static loading test
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The document discusses the Osterberg Cell static loading test method for testing bored piles as an alternative to conventional static loading tests. It provides three key advantages: (1) It requires no overhead reaction system, making testing more economical and safe; (2) It separately measures side shear and end bearing load capacities; (3) It can test piles to near their ultimate capacities. The document describes the equipment, history, advantages, limitations and interpretation of Osterberg Cell test results.
The osterberg cell static loading test
- 1. The Osterberg Cell Static Loading Test Utilizing The Osterberg Cell for Loading test instead of Conventional Static LoadingTest 12/12/2016 Alaa Mohamed Metwally 1
- 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. 12/12/2016 Alaa Mohamed Metwally 2
- 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. 12/12/2016 Alaa Mohamed Metwally 3
- 4. 1. Introduction 12/12/2016 Alaa Mohamed Metwally 4 Osterberg Cell
- 5. 2. Static load testing using O Cell 12/12/2016 Alaa Mohamed Metwally 5 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. 12/12/2016 Alaa Mohamed Metwally 6
- 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. 12/12/2016 Alaa Mohamed Metwally 8
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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. 12/12/2016 Alaa Mohamed Metwally 10
- 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 12/12/2016 Alaa Mohamed Metwally 11
- 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 12/12/2016 Alaa Mohamed Metwally 12
- 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. 12/12/2016 Alaa Mohamed Metwally 13
- 14. 7. Test results 12/12/2016 Alaa Mohamed Metwally 14 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. 12/12/2016 Alaa Mohamed Metwally -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. 12/12/2016 Alaa Mohamed Metwally 16
- 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 12/12/2016 Alaa Mohamed Metwally 17
- 18. Presented By Student at Nile Academy for Science and Technology Code: 130326 Due date: 9-12-2016 12/12/2016 Alaa Mohamed Metwally 18