Driven piles refusal,embedment and reinforced tips?

[soils212]

Looking for general rule on refusal with driven H piles into bedrock (Shale). This is a road bridge project. The site has 30 to 40 feet of soft clays over shale which has 50 blows for 4 inches about 3 to 5 feet into the shale. Have seen 10 to 15 blows for an inch for refusal. Is a minimum embedment into bedrock typically given or is it totally controlled by refusal? We are looking at 10 feet. When are reinforced tips usually recommended?

 

[GeoPaveTraffic]

The tips are just to limit damage to the piles.

I doubt you will be able to drive the piles 10 feet into the shale. Minimum penetrations are often given, but that does not mean that you can drive the piles that far.

 

[SlideRuleEra]

GeoPaveTraffic has provided the information you need. I'll add just one comment. In situations, such as yours, pile points are NOT advisable - "The enlarged bottom of the pile will cause the pile to refuse at a higher elevation...". See page 42 of "Bethlehem Steel H Piles", which you can download from this page of my website:

http://www.slideruleera.net/Steel-Piling.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

With the comment by SlideRuleEra suggesting no tips, then comes the question for this site. If there is refusal on the top of the shale, is that any less support capability than a crimpled end pile that gets into the shale "maybe" or doglegged on top of it?

I've had a few tests done by puling piles done each way. I'd have more confidence in those with tips here.

I'd have to guess that scour here will never reach the rock, so lateral support for the piles is not a question for this site. Then, why any embedment requirement?

 

[DRC1]

A really rough rule of thumb dating back to an old (but good) ASCE pile driving guide is 5 blows per 1/4 inch for rock. (This is not the same as 20 blows per inch)You will not go 10 feet into the shale. The best way to check termination blow count is to use a wave equation. Tips will depend on driving stresses and conditions, as well as dip of bedrock. However, like chicken soup, when in doubt they can't hurt. Note that many shales will relax after driving and some local experince should be sought.