O-Cell Testing

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3 O-cell me 2005.jpg Description of the Osterberg Cell

The award winning Osterberg Cell, or "O-Cell', gets its name from the inventor, Dr. Jorj O. Osterberg. The O-cell is a hydraulically driven, high capacity, sacrificial loading device installed within the foundation unit. Working in two directions, upward against side-shear and downward against end-bearing, the O-cell automatically separates the resistance parameters. By virtue of its installation within the foundation member, the Osterberg Cell load test is not restricted by overhead structural beams and tie-down piles. Instead, the O-cell derives all reaction from the soil and/or rock system. End bearing provides reaction for the skin friction portion of the O-cell load test, and skin friction provides reaction for the end bearing portion of the test. Load testing with the O-cell continues until one of three things occurs: ultimate skin friction capacity is reached, ultimate end bearing capacity is reached, or the maximum O-cell capacity is reached.

Each Osterberg Cell is specially instrumented to allow for direct measurement of the expansion so with compression and top of pile shaft measurements the downward end bearing movement and the upward skin friction movement are known. O-cells range in capacities from 0.7 MN to 27 MN. By using multiple O-cells on a single horizontal plane, the available test capacity can be increased to more than 200 MN. By utilizing multiple O-cells on different planes, distinct elements within a shaft or pile can be isolated for testing. Using the O-cell, LOADTEST, Inc. has elevated the application of deep foundation load testing, from expensive time consuming small scale field tests, to state-of-the-art short duration full scale load testing of production shafts and piles.

The O-cell Advantages

DESIGN: Excellent tool for value engineering foundation redesign.

HIGH TEST LOAD CAPACITIES: Test loads routinely exceed 27 MN, however, O-cell test capacities are available from 0.44 MN to greater than 200 MN under suitable conditions.

REDUCED WORK AREA: Required work area (overhead and laterally) is greatly reduced vs. any other static load testing system. Testing has been performed inside buildings, under overpasses, in narrow interstate/highway median strips and off-shore.

TIME: Testing is performed once concrete has reached suitable strength. (which typically takes 7-14 days from pile installation)

IMPROVED SAFETY: No reaction system is required at ground level and the test energy is safely buried well below ground.

ROCK SOCKETS: High test loads can be applied directly on deeply buried rock or soil formations without load shedding in overlaying soils, which eliminates the need for de-bonding techniques.

DEEP CUT-OFF LEVELS: O-cell testing with deep cut-off levels below ground can be performed; eliminating pile extensions to ground level and pile head preparations.

PILES WITH PLUNGE COLUMNS: Where steel columns have been cast in the top of the pile, these often interfere with top-down testing techniques, and the O-cell testing method is likely to be the only cost effective way of performing a full scale static load tests on these piles.

ACCURACY: Since there are no anchors, reaction piles or a reaction mass required, the influences, in terms of modified test pile performance, resulting from the construction and the use of anchors, reaction piles or a reaction mass required in top-down static testing, are eliminated.

ECONOMY: The O-cell method becomes more economical as loads increase, unlike top-down static tests.

SHEAR / END BEARING COMPONENTS: The O-cell tests are designed to separate test piles into 2 or 3 pile sections; thus automatically measuring the reaction of each of the components.

AUTOMATION / STATIC CREEP EFFECTS: The O-cell test is a static maintained load test and uses automatic data acquisition techniques and load maintenance for accurate, efficient data processing and creep measurements.

PRODUCTION PILES: Post-test grouting techniques allow for testing of production piles.

PERFORMANCE: The subsequent performance of O-cell tested production piles will be similar to the non-tested production piles due to the lower amount of generated residual stresses in the pile, as compared to applying full test loads "top-down."

OFF-SHORE: The O-cell test method particularly excels in off-shore testing environments due to its numerous advantages illustrated above.

Patent US5,576,494

O-Cell Testing

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