What is pile rake?
Pile rake (Dutch: schoorstand) is the deliberate inclination of a structural member from the vertical, typically a foundation pile. A pile installed this way is called a raking or battered pile.
It should not be confused with unintended out-of-plumb deviation of a driven pile. If that exceeds the permitted tolerance, the pile may be rejected.
How rake is expressed
Rake is given as a ratio, for example 5:1: 5 units vertical to 1 unit horizontal. Examples:
- 5:1 is about 11° from the vertical.
- 3:1 is about 18° from the vertical.
- 1:1 is 45°; this occurs for example with tension piles or grouted anchors behind quay walls.
Note: for ramps and driveways the opposite notation 1:5 is common (1 up for 5 across). Raking piles are also sometimes wrongly labelled 1:3 when 3:1 is meant. When in doubt, check the drawing or ask.
Application
Raking piles are used where a foundation must resist horizontal as well as vertical loads, for example at bridge abutments, quay walls, retaining walls and piers. They are usually combined with vertical piles, with the rake opposing the direction of the horizontal force.
Points to watch:
- Design: the acceptable rake depends on the horizontal load, pile type, pile length, soil type and pile spacing, among other things. This is determined by the structural or geotechnical engineer.
- Connection: the joint between the raking pile and the pile cap or abutment needs special attention, because under lateral load the pile tends to break out of the foundation.
- Installation: driving raking piles requires a rig whose leader can be set at the correct angle. Check and record the angle during driving in the pile log.
- Settlement: in compressible soils, ground settling around a raking pile can induce additional bending in the pile.
Related Terms
- Pile
- Pile driving record
- Bridge abutment
- Retaining wall
- Grouted anchor
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