Self Balancing - The safe, green, fast and economical pile load test method
09/08/2016
Introduction
Load test is works to do in most of the projects using pile foundation, especially using bored pile, barrette. The usual testing method is static compression load test used mostly counterweight concrete blocks or anchor pile system; the dynamic load test method (PDA); the quick load test method. Nowaday, there is a static load test method being applied widely in the world by the outstanding features is the Self Balancing Test Method ( might be called Osterberg Cell Load Test, Bi-Directional static load test). We would like to introduce a summary of the main issues of this method.
Self Balancing Load Test method
Testing method
The basic principle of this method is to use a load box (combined by one or more hydraulic jacks) located inside the pile body in a position to be calculated in advance before install pile, together the system the displacement gauges and strain gauges. When loading, the load box will load of 2 directions makes movement of two half piles, record and measure the relationship between load and displacement of pile body can calculate the load capacity of the test pile. The principle of this method is shown in following figure (b and c) below:
Compare the Self Balancing Test method with another satic load test method.
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The Self Balancing Test Method
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Vertical Compression Load Test using counterweight concrete block
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Vertical Compression Load Test using anchor pile system |
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- Low cost and simple method
- Low quantity of mobilization of testing equipment
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- High cost (especially far projects)
- High quantity of mobilization of testing equipment, vehicles cause smoke, dust and traffic jams.
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- High cost (due to construction of the anchor piles)
- High quantity of mobilization of testing equipment, vehicles cause smoke, dust and traffic jams. |
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Larger test load, cheaper costs
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Larger test load, larger costs (due to reinforce two bearings foundation)
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Larger test load, larger costs
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Not limit load test
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Apply to test load is smaller than 4500 ton per pile
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Apply to test load is smaller than 6000 ton per pile
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Preparation time: ≤ 2 days
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Preparation time: 7-10 days
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Preparation time: 10-12 days |
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No require the large construction site
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Require the large construction site
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Require the large construction site |
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Safety
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Dangerous and especially dangerous when large test load and soft ground.
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Danger
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Can be performed for offshore piles
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Can't be performed for offshore piles
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Hard to perform for offshore piles
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Testing result:
- When loading from the load box, pile will be split into 2 parts, measured movements of the upper and lower part of the pile, the relationship curves between load and displacement as follows::
- Converted to equivalent relationship curve between load and displacement at the head pile will have a relationship chart as static vertical compression load tests as follows
- Can determine the load capacity of test pile (ultimate load or safe load).
Self Balacing method in Vietnam
- The Self Balancing test method (Osterberg Load Test) was applied for the first time in 1995 in Vietcombank Tower Project (Hanoi) for barrette with testing load 1200 Tons. In 1997, applied for bored pile of the My Thuan bridge with testing load 3600 tons. The works were carried out by the LOADTEST Company (American company). Since then there are also some other works done by this method and are performed by foreign companies . Because these projects are using equipment and foreign experts should prices remain high, it is difficult to apply common.
- In 2011, a group of ADCOM Consultants engineer (including Master Nguyen Minh Hai - currently is PhD student in geotechnical and foundation at the University of Arlington, Texas, US and Mr Le Nguyen Tinh - currently General Director of ADCOM Consultants) began studying the application of this technology by the localization devices. ADCOM has successfully applied using load box manufactured in Vietnam in the Red River Bridge of project Noi Bai - Lao Cai Highway with testing load 2500 Tons.
- In May, 2016, ADCOM continued successful implementation of this method for two piles of T28 and T29 pier at Bach Dang Bridge Project with testing load is 3357T and 3235T respectively. By successfull project, engineers ADCOM confirmed to mastered the technology from the design, manufacture, installation of equipment, test and results processing. In this project, we saved half of testing pile cost for Investor than foreign agency.
Some ADCOM 's photos of the Self Balancing Test Method:
