Pile Damage
Dynamic Load Tests in general can be used to detect pile damage.
Example 1:
The soil borings indicate loose/ soft soil in the top 30-ft (10-m).
From 30-ft to 60-ft (20-m), soils are somewhat similar to FL-6 in Example 2 below:
a thin lens of relatively hard limestone (SPT N=50/4" or 50/6").
followed by a thick lens up to 10-ft of soft limestone (N generally less than 30).
then sandwiched with thin and thick lenses of the above 2 materials.
It appeared the pile toe might have deflected along the rock slope and followed the path of the least resistance, despite the high rigidity of the pile material.
Example 2:
Concrete Pile, 18-in (45-cm) square, 60-ft (18-m) long. Prestressed. No joint (no splice).
Allowable driving stress limits:
TSX < 1.5 ksi (10 MPa)
CSX, CSB < 3.5 ksi (23 MPa)
During the drive, all stresses were much smaller than the tolerable limits.
Tested using PDA in 2011. Similar GPC data is presented @ the end of this page.
Pile 4L-2 damaged when TSX = 0, pile toe at EL - 4.1 ft. BTA=67%. Pile extraction could cause further damage.
The damage was due to pile toe walking away on a sloping surface, while pile top was fixed vertically.
Example 3:
Pile extraction shows very minor damage (could have been accepted if Pile Resistance exceeded the Required NBR)
Due to damage at Pile 4L-2, subsequent piles were stopped even @ BTA=90%.
This Pile 3R-2 was rejected when BTA=90% and resistance was only 180 kips (Required Load NBR=388 kips). Pile toe at EL -7.5 ft. CSX, TSX, CSB were all less than 40% of allowable limits through out the drive.
If pile were to be driven further trying to get Required NBR, damage could be worsening.
Examples 4, 5, 6, 7: Please find these piles in Links. These piles behave similar to Pile 3R-2 (Example 3 above).
GPC file Dolphin 2.tdms (14-in square)
GPC files Pile 6-1, 6-3, 6-9 (24-in square)
Example 8: Clear damage at the splice of a concrete pile. Possible reason(s): i) poor splice welding; ii) installation of a large group of production piles, which caused pile rebound of previous installed piles - these rebounds might have pulled the pile tops up (while pile bottoms stayed).
Question: If BTA < 80%, does it mean the pile is damaged?
Answer: Not always. BTA < 80% and the pile may have no damage in some cases, for example in case where there is unloading skin friction. Consult an experienced engineer to evaluate the pile integrity.
Question: If BTA > 80%, does it mean the pile has no damage?
Answer: Not always. Example 3 above shows a pile with very minor damage when BTA=90%. Please note that when BTA > 90% (such as 90.01%), some other program (not GPC) will round it up to 100%.