How far back can i perform an excavation without affecting the side friction of existing piles? 3

[pelelo]

Engineers,

I am working on an excavation project and adjacent to the excavation there are existing 18-inch concrete piles.

My question is how far back in the excavation i can go ("d") without affecting the side friction capacity of the piles?, is there any rule of thumb or radius of influence?

I am not sure about this.

Please refer to the sketch attached.

Please advise.

 

[oldestguy]

A lot depends on loads on them and their depth as well as soil type.

Off haNd I'd say once your excavation is to the depth of that figure "d" then you start taking away support of the closest piles.

Treatment types for this are several. One for sure thing is install braced sheet piles between your excavation and the pile next to the site. Otherwise be prepared for major problems now and LATER..

 

[SlideRuleEra]

For minimum distance, I would use a clear separation between the wall and closest pile of 5 pile diameters or 8 feet, which ever is greater. This is the same minimum required for:

a) Federal Highway Administration calculations of pile group efficiency to be 1.0 (no interaction).

Note that 6 pile diameters center-to-center = 5 pile diameter clear separation

b) ASTM-D1143 Axial Pile Load Test clearance between anchor piles and test piles.

http://www.SlideRuleEra.net

 

[oldestguy]

Slide rule era. Sorry but your references are for completed work, not the excavation for construction. Being that the piles are in a group the critical distance is even less than for a single pile. In addition to worrying about this distance, settlement or elevations of the adjacent structure must be started before any excavation.

 

[HENRYZAU]

I would go for 4xD as a minimum, but the excavation-induced lateral deflection effects on the existing piles may be more critical.