A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Dynamic Load Testing of Drilled Shafts at National Geotechnical Experimentation Sites
Due to their quick and simple execution, dynamic load testing is a preferred method of Quality Assurance in the United States and around the world for both driven piles and drilled shafts. The test is particularly simple for driven piles, where the loading apparatus, the pile driving hammer, is readily available. To perform the test, strain and acceleration are measured a short distance below the pile top. The strain multiplied by the pile material's elastic modulus and the pile's cross sectional area yields the pile top force. For prefabricated, driven piles the elastic modulus varies only slightly over the cross section, and two strain transducers mounted to opposite sides of the pile usually yield the true average strain. For drilled shafts, the effort is somewhat more involved because a ram must be brought to the construction site. A crane or free release system must then drop this ram from heights ranging from 0.3 to 3 m. The acceleration and strain measurements are typically acquired one or two pile diameters below the pile top. Since bored piles without permanent casing often have uncertain cross sectional and concrete material properties, it is generally best to add a pile top extension of a thin steel pipe, one to two pile diameters long and filled with good quality concrete. The sensors are then anchored directly to the concrete after removing the steel from the attachment area. Frequently four strain sensors are utilized to improve the measured average strain because of possible variations in concrete quality and strain magnitudes over the cross section (Figure 1). The steel pipe also acts as external reinforcement and prevents the concrete from spalling due to the impact of the drop weight. A recent development has combined the measurement system with the dynamic loading system, improving and simplifying the measurements. The acceleration is still measured at the pile top, but the pile top force is calculated from the product of the ram's mass and its measured deceleration. This paper describes dynamic pile tests recently conducted with both strain and ram mounted force measurements at the Federal Highway Administration's National Geotechnical Experimentation Sites in Amherst, Massachusetts and Opelika, Alabama. It compares the dynamic pile testing results to static load tests and rapid load tests (Statnamic) performed at the sites prior to the dynamic testing.
Dynamic Load Testing of Drilled Shafts at National Geotechnical Experimentation Sites
Due to their quick and simple execution, dynamic load testing is a preferred method of Quality Assurance in the United States and around the world for both driven piles and drilled shafts. The test is particularly simple for driven piles, where the loading apparatus, the pile driving hammer, is readily available. To perform the test, strain and acceleration are measured a short distance below the pile top. The strain multiplied by the pile material's elastic modulus and the pile's cross sectional area yields the pile top force. For prefabricated, driven piles the elastic modulus varies only slightly over the cross section, and two strain transducers mounted to opposite sides of the pile usually yield the true average strain. For drilled shafts, the effort is somewhat more involved because a ram must be brought to the construction site. A crane or free release system must then drop this ram from heights ranging from 0.3 to 3 m. The acceleration and strain measurements are typically acquired one or two pile diameters below the pile top. Since bored piles without permanent casing often have uncertain cross sectional and concrete material properties, it is generally best to add a pile top extension of a thin steel pipe, one to two pile diameters long and filled with good quality concrete. The sensors are then anchored directly to the concrete after removing the steel from the attachment area. Frequently four strain sensors are utilized to improve the measured average strain because of possible variations in concrete quality and strain magnitudes over the cross section (Figure 1). The steel pipe also acts as external reinforcement and prevents the concrete from spalling due to the impact of the drop weight. A recent development has combined the measurement system with the dynamic loading system, improving and simplifying the measurements. The acceleration is still measured at the pile top, but the pile top force is calculated from the product of the ram's mass and its measured deceleration. This paper describes dynamic pile tests recently conducted with both strain and ram mounted force measurements at the Federal Highway Administration's National Geotechnical Experimentation Sites in Amherst, Massachusetts and Opelika, Alabama. It compares the dynamic pile testing results to static load tests and rapid load tests (Statnamic) performed at the sites prior to the dynamic testing.
Dynamic Load Testing of Drilled Shafts at National Geotechnical Experimentation Sites
Robinson, Brent (author) / Rausche, Frank (author) / Likins, Garland (author) / Ealy, Carl (author)
International Deep Foundations Congress 2002 ; 2002 ; Orlando, Florida, United States
Deep Foundations 2002 ; 851-867
2002-02-01
Conference paper
Electronic Resource
English
Dynamic Load Testing of Drilled Shafts at National Geotechnical Experimentation Sites
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