Consolidation settlement of group piles

[Jaelle]

When estimating consolidation settlement of group piles, should we assume that the load transmitted to the soil is the total load of the superstructure, or is it reduced by skin friction effect?

 

[gotwood]

I dont think you reduce the skin friction.

 

[drobi]

Jaelle

I assume that you are talking about a group of piles in a cohesive soil. Tomlinson in his book 'Pile design and construction practice', suggests that it should be assumed that the pile group behaves as a block foundation with a certain amount of flexibility, depending on the capping system and the structure.

He suggests that 'Load transfer in skin friction from the pile shaft to the surrounding soil is allowed for by assuming that the load is spread from the shafts of friction piles at an angle of 1 in 4 from the vertical'.

In simple terms he suggests that the TOTAL load on any pile cap is spread out at 1 in 4 from the outer piles of the group, to represent an 'equivalent raft foundation' at a depth of 2/3 the pile length. The settlement of this equivalent raft can the be calculated using standard procedures.

Sounds complicated but when you sketch it out it is relatively straight forward and hopefully answers your question.

Good luck

 

[fattdad]

what drobi said. this is exactly what I was taught in college and what I do. There are some practical considerations, being if the pile group penetrates 30 ft of soft clay and into 10 ft of dense sand, the 2/3rds point would then suggest taking the consolidation properties into account in evaluating the pile group settlelent. Somewhere in this you also have to look at the geology and use common sense.

f-d