relation of tip shape and piles end bearing

[ksaberi]

Please tell me if there is any relation between tip shape of a precast concrete driven pile and its end bearing? if dimension of the section of pile is 400x400mm with a piramid tip, is it suitable to design the tip with a 300mm height piramid? The SPT of soil at the tip is greater than 50.

 

[ishvaaag]

A 1 point tip I don't see in the examples in my books and sheets. Cuts are shown be at 45 deg, then flat. This even true when the tip steel reinforced. However it might work, since it is not dissimilar and penetration stresses get lower.

Respect end bearing I assume the same assumption may be made regardless of the shape of the tip shape, since piles will be driven more or less to same refusal status by the driving machines.

 

[ishvaaag]

Also note that piles with pointed tips tend to lose proper alignment, and so maybe using less or no point may be better.

 

[ayfarm]

In normal practice, concrete piles tips are not pointed at all, they are just square ended. Points tend to wander and break during driving especially in rock or dense gravelly layers. Pile top & tip spirals are spaced closer and the addition of a steel bar hoops will help especially during hard driving. The next step is to cast a steel HP stinger if deemed helpfull. Let me know if u desire more detailed info.

 

[learnerydy]

This question is for ayfarm. If a HP14 stinger with length of , let's say, 3 ft is attached to a 24" square concrete pile tip to facilitate driving and the pile is driving to seat on strong rock with allowable copressive capacity of 60 tsf, the overlying soil is very soft clay with possible boulder, how to calculat the end bearing? does the end bearing depend on the HP section? We know that the section aera of concrete is much greater than the area of stinger

 

[ayfarm]

To learnerydy,
The HP stinger will dictate the end bearing capacity of the driven pile as a unit. The weakest joint is the splice between concrete and steel. This joint will always break first than any portion of pile. Before the tip hits the rock, assuming the pile "runs" during "pushing" thru the soft overlay, there will be a sudden stop in the rate of penetration and hammer will bounce quite a bit. Assuming the tip is still intack (you can lose it like a torpedo) when that big bang of the hammer hit the pile, this is where cracking and spalling occurs. The WEAP and PDA picture showing stresses, energy and the whole shebang will tell you the capacity, stresses and all the good stuff you want to knonw. Pile driving formulas do not tell much but should you elect to use one, the Danish formula will give better results as it is more used often. Stingers are not intended to "seat" piles in rock, they are intended to penetrate intermediate hard pan layers before you get to the desired tip. The design objective is to satisfy required BRG/Tension and lateral capacity/delta of the given pile. There are lots of projects that I got involved where the stingers were eventually cut-off & scrapped. Roque Engineers

 

[aji1]

Tell me about stress below a pile group and how soil behavior betwen pile group if foundation has been block failure or single failure, and wich using formula/ theory ?

 

[BigH]

aji1: See M.J. Tomlinson Design and Construction of Piles, ViewPoint Publications.

Good thread.

 

[elfatosman]

dear sir

how can i design a pile in expansive soils, economically and safetly ( pls give me a guid lines )..
regards