Counting Blow Counts While Pile Driving

[cive316]

Relatively fresh engineer/inspector here. Currently on my second job with pile driving. Looking for any advice/tips that others use to set a "datum" to measure blows per foot by. On my previous job I would mark 1' increments on the pile and then put a mark on the leads and use that as my reference (hope that makes sense). That worked fine but sometimes the leads would move or shift or the pile would spin slightly (shell pile) and my marked "datum" wouldn't be visible with the 1' markings on the pile. Any other ideas? Thanks.

 

[GeoPaveTraffic]

Not really, just need to find something to use as a reference point.

Many times the ground surface is the best point to use.

Mike Lambert

 

[Ron]

One foot markings are fine for the gross driving. You will need to go to 1-inch measurements at take-up. For that you can use a steel ruler. I marked mine with red magic marker so it was easier to see.

 

[BUGGAR]

I once read blow counts with a hand level when there was no other stable reference point. I was close enough to get a decent read, though.

 

[concretemasonry]

civie316 -

That sounds like my challenge as my first job as field inspector for the highway department (engineering student on a summer job). We were driving freshly creosoted wood piles for freeway bridges and abutments on a 85-90F day. Since I was new, they gave me the OPPORTUNITY(?) to determine when we got deep enough.

We used one or two saw horses with grooves as a guide for a long steel rod with a spike to determine the driving distance every ten blows ( the criteria was 1" per 10 blows). The levelness of the rod/spike was not too critical since the closest saw horse was close to the wood piling.

When I got home that day, I had burns on my arms, back and front(through my shirt) from the hot, fresh creosote and oil from the driver. - It was a great experience that I never will forget, and it not necessary to get so close since you are looking at a relative driving length if you are close to the piles. - I was the eager "greenie" that everyone thought needed some experience.

Long steel piles are a different story. In another episode as a project engineer we were driving long steel piles (some spliced) through a mine waste dump where the anticipated solid rock bearing was about 70' to 100'. We had a pile that was spliced and driving continued and we had to decide if we wanted to go deeper. We got my answer when I leaned against another previously driven pile 50' feet away that resounded when the driver hit. - The pile had hit a large (2' - 6') rock from the stripping and got deflected and bent in a large curve horizontally about 50'. Keep in mind that steel pile can be gradually deflected and may not got directly in line with the surface exposure above grade.

don't split hairs for a 1" increment.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Panars]

We will sometimes lay a piece of wood on the ground near the pile. It provides a straighter line than the ground surface.

 

[dicksewerrat]

We marked the pile hammer guides with paint at 1 foot increments. Watched the pipe cap. No problems, didn't get that nasty creosote all over.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[SlideRuleEra]

As a bridge contractor, we had to adjust the technique to the situation. For piling on land, we would stand a typical 4' spirit level on end - one end touching the pile, the other on the ground. Between hammer blows make a horizontal mark on the pile, with soapstone, at the top end of the level. After a selected number of hammer blows, make another horizontal mark on the pile, at the top end of the level. The distance between the marks is how far the pile penetrated in the selected number of blows. A little math, and you have blows per inch.

Note that the 4' spirit level is not being used in any way as a level. It is just a straight jobsite tool at hand. The level would be used, as a level, to establish the pile's slope when driving of a batter pile is started.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[BigH]

I remember one of my first jobs - the others gave advice on the pile you were driving. We had some pile groups and I had wanted to investigate what happened to the first and second pile of the group when subsequent piles were driven . . . client lent me a surveyor and we strapped on a tape measure on the already driven piles and took level readings as the last pile was driven. It was interesting to see where a slight heave occurred when the driven pile hit the glacial till (above the till was fill).

 

[BigH]

Further to Dick's observation about deflection of pile, Bengt Fellenius wrote a short piece on "What Goes Down Comes Up - Sometimes" in Geotechnical News, Vol 1 No. 4, page 13. I'll let the pictures extracted from the piece as attached tell the story!

 

[GeoPaveTraffic]

I have always loved that picture BigH. Can't count the times I've used that example of what can happen when driving piles.

Mike Lambert