M. Prezzi
Assist. Prof., School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
R. Salgado
Prof., School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
D. Basu
Ph.D. Student, School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
K. Paik
Assoc. Prof., Dept. of Civil Engineering, Kwandong Univ., Kangwon-do, South Korea
J. Lee
Assist. Prof., School of Civil Engineering, Yonsei Univ., Seoul, South Korea
Piles are classified into displacement (driven) and non-displacement (bored) piles, depending on their methods of installation. The installation method (driving or boring) has a significant effect on the pile static capacity for the level of settlements we allow in design. The state of the soil (density and stress state) is changed significantly when a pile is driven into the ground (Lee et al. 2003). Thus, design of non-displacement piles (e.g. drilled shafts) can be based on the original (before pile installation) in-situ states of soils, but the design of displacement piles (e.g. open- and closed-ended pipe piles, H-piles) must account for the changed soil states. The matter is further complicated for open-ended pipe piles, which often show responses that are in between those of non-displacement and full displacement piles.
During the driving of open-ended pipe piles, some amount of soil will initially enter into the hollow pipe. Depending on the soil state (dense or loose) and type (fine-grained or coarsegrained), diameter and length of pile, and the driving technique, the soil inside the pile may or may not allow further entry of soil into the pipe. If soil enters the pipe throughout the driving process, driving is said to take place in a fully coring mode and the behavior is more like that of a non-displacement pile. However, if the soil forms a plug at the pile base that does not allow further entry of soil, then driving is said to be done in a fully plugged mode. If a pile were driven in the plugged mode during all of the driving, its load response would approach that of a displacement pile. In real field conditions, the behavior is generally in between the fully plugged and coring modes. Further, depending on whether a pipe is jacked or driven into the ground, the behavior is different (Paik and Salgado 2004).
The research carried out at Purdue University on the analysis and design of drilled shafts and open- and closed-ended piles was reviewed. Both numerical analysis and experiments (field and calibration chamber tests) were done to assess the behavior of these piles, taking into account the role of the different soil properties and the loading processes associated with the different installation methods. The resulting unit base and shaft resistances were found to depend on relative density and horizontal stress for drilled shafts and closed-ended piles, and also on IFR for open-ended piles.
The base resistance of a displacement pile is more than that of a geometrically identical drilled shaft. Moreover, the capacity of a closed-ended driven pile is more than that of an openended pile of same outer diameter. Further, the normalized shaft resistances are less in magnitude compared to the corresponding base resistances.
The strongest effect on normalized unit base resistance is that of the relative density; the normalized resistance decreases as relative density increases. The shaft resistance, on the other hand, shows a larger scatter when plotted against relative density. Since the results are presented by taking into account the various effects of soil state and the loading process, these can be readily used for design. However, the values of base resistances for closed-ended displacement piles, extrapolated from the non-displacement pile analysis by considering values available in the literature, should be used with caution because of the large amount of variability involved in the values.
This paper, thus, proposes that pile design for axial loads be done in terms of unit resistances, normalized with respect to cone resistances, for given settlement levels for vertically loaded piles. The research done at Purdue University in the past decade offers some guidance on what these values should be.
Read more: Monica Prezzi
Assist. Prof., School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
R. Salgado
Prof., School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
D. Basu
Ph.D. Student, School of Civil Engineering, Purdue Univ., W. Lafayette, IN, 47907, USA
K. Paik
Assoc. Prof., Dept. of Civil Engineering, Kwandong Univ., Kangwon-do, South Korea
J. Lee
Assist. Prof., School of Civil Engineering, Yonsei Univ., Seoul, South Korea
Piles are classified into displacement (driven) and non-displacement (bored) piles, depending on their methods of installation. The installation method (driving or boring) has a significant effect on the pile static capacity for the level of settlements we allow in design. The state of the soil (density and stress state) is changed significantly when a pile is driven into the ground (Lee et al. 2003). Thus, design of non-displacement piles (e.g. drilled shafts) can be based on the original (before pile installation) in-situ states of soils, but the design of displacement piles (e.g. open- and closed-ended pipe piles, H-piles) must account for the changed soil states. The matter is further complicated for open-ended pipe piles, which often show responses that are in between those of non-displacement and full displacement piles.
During the driving of open-ended pipe piles, some amount of soil will initially enter into the hollow pipe. Depending on the soil state (dense or loose) and type (fine-grained or coarsegrained), diameter and length of pile, and the driving technique, the soil inside the pile may or may not allow further entry of soil into the pipe. If soil enters the pipe throughout the driving process, driving is said to take place in a fully coring mode and the behavior is more like that of a non-displacement pile. However, if the soil forms a plug at the pile base that does not allow further entry of soil, then driving is said to be done in a fully plugged mode. If a pile were driven in the plugged mode during all of the driving, its load response would approach that of a displacement pile. In real field conditions, the behavior is generally in between the fully plugged and coring modes. Further, depending on whether a pipe is jacked or driven into the ground, the behavior is different (Paik and Salgado 2004).
The research carried out at Purdue University on the analysis and design of drilled shafts and open- and closed-ended piles was reviewed. Both numerical analysis and experiments (field and calibration chamber tests) were done to assess the behavior of these piles, taking into account the role of the different soil properties and the loading processes associated with the different installation methods. The resulting unit base and shaft resistances were found to depend on relative density and horizontal stress for drilled shafts and closed-ended piles, and also on IFR for open-ended piles.
The base resistance of a displacement pile is more than that of a geometrically identical drilled shaft. Moreover, the capacity of a closed-ended driven pile is more than that of an openended pile of same outer diameter. Further, the normalized shaft resistances are less in magnitude compared to the corresponding base resistances.
The strongest effect on normalized unit base resistance is that of the relative density; the normalized resistance decreases as relative density increases. The shaft resistance, on the other hand, shows a larger scatter when plotted against relative density. Since the results are presented by taking into account the various effects of soil state and the loading process, these can be readily used for design. However, the values of base resistances for closed-ended displacement piles, extrapolated from the non-displacement pile analysis by considering values available in the literature, should be used with caution because of the large amount of variability involved in the values.
This paper, thus, proposes that pile design for axial loads be done in terms of unit resistances, normalized with respect to cone resistances, for given settlement levels for vertically loaded piles. The research done at Purdue University in the past decade offers some guidance on what these values should be.
Read more: Monica Prezzi
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