Plugging effect of open-ended piles in sandy soil

Ko, JaeYoun; Jeong, Sangseom

doi:10.1139/cgj-2014-0041

Cited by 50 publications

(18 citation statements)

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“…Note that the inner diameter of the test pile was only 250 mm and thus it was difficult to install strain gauges inside the pile. To measure the annulus resistance of the pile base and the soil plug resistance separately, double-walled pile systems have been used for open-ended steel pipe piles in calibration chambers (e.g., Lehane and Gavin 2001;Paik et al 2003) and in the field (e.g., Ko and Jeong 2015). However, the double-walled pile method is not applicable to concrete piles as the wall thickness is significantly larger than steel pipe piles.…”

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Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

et al. 2017

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We thank the Discussers for their interest in our paper (Kou et al. 2016). We agree that the jacking of adjacent piles could cause a tensile effect when the center-to-center distance between two adjacent piles is small. However, as this is not the case for our study as pointed out by the Discussers (Zhang et al. 2017), this question is irrelevant. As explained in the paper, residual forces are usually caused by pile compression, rebound of the soil at the pile base, and the soil strength recovery after installation. If the distance between adjacent piles is small, the tensile effect caused by the installation of adjacent piles will push the pile upward and reduce the residual forces in the pile.We were well aware of the temperature effect on the wavelength of fiber Brag grating (FBG) strain sensors during monitoring. It was for this reason that the field tests presented in the paper were conducted in June and July where the temperature variation was small during the day.In the paper, residual force refers to the compressive force caused by the elastic compression of the pile. This elastic compression is mainly caused by jacking force, shaft resistance, and base resistance. The jacking force plays a key role during the process. After installation, the pile recovers from the elastic deformation. There are two types of forces preventing the pile recovering from the elastic deformation after installation. One is the shear force between the soil and pile, which is enhanced due to the dissipation of excess pore-water pressures. The other is the additional downward force caused by the settlement of the ground, which is also caused by the dissipation of pore-water pressures. Note that the additional downward force can prevent the pile from recovering from the elastic deformation. If the additional downward force causes the residual forces to increase, it means that the deformation caused by the additional downward force is larger than the initial elastic deformation. However, this is almost impossible because the force that caused the initial elastic deformation is larger than the additional downward force. Therefore, for a pile after installation, residual forces would decrease until the recovering force, shear force, and additional downward force reach an equilibrium state.The measured base resistance presented in the paper included both annulus resistance of the pile base and soil plug resistance. Figure 4 in the paper shows the arrangement of strain sensors along the test pile. Note that the inner diameter of the test pile was only 250 mm and thus it was difficult to install strain gauges inside the pile. To measure the annulus resistance of the pile base and the soil plug resistance separately, double-walled pile systems have been used for open-ended steel pipe piles in calibration chambers (e.g., Lehane and Gavin 2001;Paik et al. 2003) and in the field (e.g., Ko and Jeong 2015). However, the double-walled pile method is not applicable to concrete piles as the wall thickness is significantly larger than steel pipe ...

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Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

et al. 2017

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Discussion of “Plugging effect of open-ended piles in sandy soil”

Fellenius¹

2015

Can. Geotech. J.

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The authors have presented an interesting account of a fullscale study of the response of a pipe pile driven with an open toe to the presence of an inside soil column in the pile (Ko and Jeong 2015). The tests consisted of dynamic measurements during the driving and static loading tests some time after the driving on double-wall pipe piles. Strain-gage measurements were used to determine the load distribution.The double-wall test piles were fabricated with the inside pipe centered in relation to the outside pipe. The steel cross section of the outside pipe was about 10% smaller than the inside pipe. The about 40 mm "gap" or void between the outside of the inner pipe and the inside of the outer pipe was welded closed at the pile toe to prevent soil from entering the "gap". The welding resulted in a firm and fixed connection between the two pipes, ensuring that the lower ends of the two pipes moved in unison in the tests. I understand that no such fixed connection was made at the pile head. However, the lengths of the pipes were the same, which means that a plate placed on the pile head rested on both pipes enabling the upper end of both pipes to be engaged approximately simultaneously. Presumably, the dynamic gages (accelerometer and strain-gage pairs, I assume) were placed on only the outer pipe and the force delivered to the pile by the hammer impact was determined from the sum of the two pipe areas as based on the assumption of perfect connection to the pile head plate. Because the test pile was made up of a pair of pipes welded together at the lower end, I would expect that the dynamic gages will have recorded considerable reflections during the tests. I would not have expected a good correlation between the CAPWAPdetermined capacities (Table 2) and those determined by the offset limit method from the static loading tests ( fig. 11). It would be interesting if the authors could provide details of the pile and soil models employed in the dynamic analyses.As reported by the authors, development of an inside soil column and plugging during the driving of open-toe pipe piles has been addressed by several researchers. All depict the forces acting on the pipe pile during driving as similar to that shown in the authors' fig. 2, i.e., with upward-pointing shear force vectors both along the outside and inside of the pile and the inside vectors shown along the full length of the inside column. That is, the vectors indicate the forces as acting on the pipe and not on the core. The suggestion is that the open-toe pipe is forced down over the inside core.The force vectors also show soil forces acting on the steel pipe pile both at the base (Q b ) and along the inside of the shaft (Q m ), but the response cannot be both, it must be one or the other. That is, if the pile experiences a toe resistance, it has a rigid plug and there is no inside shaft shear (but for along a very short length of that rigid plug). If the pipe slides down over the core, there is inside shaft resistance, but no toe resistance. Apart from this mino...

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“…Figure 2 in Ko and Jeong (2015) represents the general bearing capacity mechanism for open-ended piles. This figure is not illustrating the force direction of the core, but rather the shaft resistance acting between the core and inside of the pile.…”

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“…As mentioned in Ko and Jeong (2015), Q plug is the smaller value of either the inner shaft resistance, Q in , or the bearing capacity of the soil beneath the plug base, Q base . Thus, if Q in is greater than Q b , the pile will fail in the plugged mode.…”

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Plugging effect of open-ended piles in sandy soil

Cited by 50 publications

References 22 publications

Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Discussion of “Plugging effect of open-ended piles in sandy soil”

Reply to the discussion by Fellenius on “Plugging effect of open-ended piles in sandy soil”

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