Short H-Piles to Bedrock
Short H-Piles to Bedrock
(OP)
We are in the type study phase of a small replacement structure. More than likely the bridge will be a single span prestressed box beam on integral abutments (single row of piling). From the geotech report, rock will be about 9' from the bottom of footing. The abutment from bottom of footing to the roadway profile grade will be around 10.5' tall.
Are there any ROT or guidance on when an end bearing pile should not be used with a short embedment depth?
We have run some preliminary numbers in Lpile and the results show about 1/2" of lateral movement in the pile at the top of rock (bottom of pile.)
Thanks,
Greg
Are there any ROT or guidance on when an end bearing pile should not be used with a short embedment depth?
We have run some preliminary numbers in Lpile and the results show about 1/2" of lateral movement in the pile at the top of rock (bottom of pile.)
Thanks,
Greg





RE: Short H-Piles to Bedrock
Another alternative is a semi-integral abutment, where the stem is integral with the superstructure and has a "pinned" connection at the top of a spread footing bearing on the bedrock. This resembles a three-sided rigid frame and was common in certain parts of the United States thirty or so years ago.
The depth of existing ground to bedrock will be an important factor in deciding which option is more appropriate.
RE: Short H-Piles to Bedrock
Many times, I have used a detail to concrete the piling in place in a pre-bored hole. This is very helpful and is not too expensive but there are other means such as loose sand placement.
crossframe - all integral endbents/abutments are assumed pinned for the purpose of analysis. The pin is taken at the abrupt change in stiffness between the pile and pile cap. As such, I don't know that a semi-integral abutment would be beneficial in the OP situation over a conventional integral abutment. With the use of neoprene pads the bridge will have to overcome shear stiffness to provide movement that is not alledgedly transferred to the piling. For low neoprene pads, the shear stiffness can be large.
Regards,
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RE: Short H-Piles to Bedrock
RE: Short H-Piles to Bedrock
Regards,
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RE: Short H-Piles to Bedrock
As an aside to your point, one of our Senior Engineers when I started up had his first drill job up in Iroquois Falls, Ontario. He was working for the Ministry of Highways. He did the first borehole and hit rock at 10 ft. (old wash boring days). He called his boss and said he'd be home in two days after he finished the second (and last) planned borehole. He ended up going home 2 weeks later - the borehole to bedrock was in excess of 100 ft!!
RE: Short H-Piles to Bedrock
The structure will be crossing a stream, so scour is a concern with spread footings. Also digging out down to the rock and then backfilling with crushed stone would require quit a bit of dewatering or temporary stream relocation which I'm sure the co. engineer isn't going to look favorbaly on.
The rock is a clayshale.
Thanks for the insight folks!
Greg
RE: Short H-Piles to Bedrock
Generally the best bet is to put in a cofferdamand put the foundation on rock, with bars grouted into rock if needed.
RE: Short H-Piles to Bedrock
RE: Short H-Piles to Bedrock