Pile Dynamic testing

This a totaly unsuitable site quit while you still can. Six stories is going to be far too greater load. Piles or no piles. Quartz will fracture very easily. Even under copression. Who ever thought this a good idea stay away from them. Also quartz rocks are very often a ground disturbance hazard. Dig a gold mine you are more likely to make money quarts and gold live together.

The problem which faces you is not uncommon (although you have not given us info as to whether the pile was driven to any given formulae ? or what was the point of refusal. This generally is a complex formulae (originally called the simple " Dutch formulae" which has now been amplified ) which utilises the weight of the hammer its method of driving i.e. gravity, air,diesel, vibratory, or now hydraulic, and a specified number of blows to achieve what is known as : the point of fixity.

Because of the nature of the soils you have indicated you should also determine what is the water level in the foundation area . You indicate limonitic soils that are probaly the most instable where water level is fluctuating. As this affects the cohesion of the soil and thus its ability (and reliability) to provide skin friction prudence should be dictated.

In fourty years of Engineering and Piling I have always shied away from skin friction as a first rule. Probably my concern has always been of the various point loads when (later and or unforeseen ) loadings that are not uniform do produce vertical stresses. Any retained soil will : it must be assumed, give rise to a lateral earth pressure equal to the surcharge ( on surface loadings) multiplied by the active earth pressure co-efficient on the whole of the active face of the foundation walls.

I draw a line here in saying that without seeing the plans of the structure and its later useage ( and its potential adjoining buildings or structures later on ) , it is unfair to give you advices , which could be seen as contrary to your design Engineers. Yet one of the other aspects that adversely affect skin friction is not only the presence of water but as well that of :earthquakes and cyclonic conditions. These can not and must not be ignored.

I hope this is of assistance to you. Labor Omnia Vincit.

I am sorry that you have missed one point that the piles are bored (cast in-situ) piles and not driven piles and therefore, point of refusal does not arise.

If you refer my original question, my worry is about two questions.

1. How far you can depend on the friction component as shown by the PDA testing?

2. In case of a negative friction assumption, the behaviour of the PDA tests?

Thanks for your comments.

The clarification you have given about this being a cored pile is noted. The bearing capacity of the pile will be a function of the quality of the material where the boring tool has ceased to penetrate the sub soil. This is where you have to be very clear.

Was the shell of the pile (or pipe whatever was used) and on which you will depend for friction driven or simply allowed to descend in the bored hole. The rule is that even if a pile is bored (except the continuous flight auger type) the outer shell if it is to be depended upon has to be driven to "refusal" . To be certain the coring of the pile should have taken place after the driving of the outer shell. Was that done ?

When visibly you have soils that are unsafe I have always used the method of an open steel shell into which a drop hammer (as near as possible of the same section of the inner pipe) ** is regularly dropped. Mortar is then inserted in the pipe and the "ramming " thereof continues. It is almost certain that the mortar , with repeated ramming of the drop hammer will form a bulge at the bottom of the pile. This is easily determined by the amount of mortar that is consumed down the hole. Once its is clear that the unsafe soil has absorbed the concrete and that a generous bulb has been formed you are then ,( that after inserting a reinforcing " cage" down the shell and concrete pouring and curing ) , re-assured that any test on the pile ( by large concrete blocks for a period of time ) will far surpass anyother result you may otherwise get . ( You can then rely on friction with more assurance of long term stability. )

**The drop hammers can easily be manufactured by a good welder-boiler maker and filled with concrete (when possible using steel scrap to make the hammer as heavy as possible). Cheap but it works (and then you can sleep at night). Presently you are not !

Labor Omnia Vincit.