Capacity of Piles installed by vibratory methods 3

[harpoon]

I have a project where the contractor is installing 4 inch steel pipe into the ground by vibratory methods. The design loads are low 15.9 kN for bearing, 3 kN for lateral and 10.2 kN for uplift. How does one calculate capacity of these piles? Can skin friction still be taken into account ? What about uplift if there is no skin friction? Soil conditions are sand to 3 m and then silt / sand and silt to 6.5 m. Does someone have any experience with this?

 

[civilperson]

Method of installation should have no bearing on the capacity of piles. Same as driven piles.

 

[hokie66]

From a structural engineer's standpoint, a 4 inch pipe pile would be a friction pile almost by default unless it end bears on rock. Determining the capacity is in the purview of the geotech.

 

[BigHarvey]

You can't predict the capacity of a pile installed by vibratory methods but given the intensity of the loads, testing them would be quite cheap !

 

[PEinc]

I thought that GRL WEAP couild run using vibratory hammers. However, I do agree with the above answers. A static analysis could still be run and these small capacity piles would be easy to load test.

 

[Panars]

The latest version of the FHWA manual on driven piles (Pub No. FHWA NHI-05-042) has this to say about vibratory hammer installed piles (Page 9-182)

"Agencies are often requested to allow pile installation with a vibratory pile hammer instead of an impact hammer. Mosher (1987) summarized the results from five sites where piles where installed by both impact and vibratory hammers. This study concluded that for a significant majority of the cases, piles installed in sand with a vibratory hammer had a lower ultimate capacity than impact driven piles at the same site. Mosher also concluded that time dependent soil strength changes occurred equally for both installation methods. Hence, the capacity of the vibratory installed piles did not increase to the capacity of the impact driven piles with time. However, it was also observed that impact driving a vibratory installed pile would increase the capacity of the vibratory installed pile to that of an impact driven pile.

O’Neill and Vipulanandan (1989) performed a laboratory evaluation of piles installed with vibratory hammers. This laboratory study found impact driven piles had a 25% greater unit shaft resistance and a 15 to 20% higher unit toe resistance than vibratory installed piles in medium dense to dense, uniform, fine sand. However, in very dense, uniform, fine sand, the impact driven pile had a 20 to 30% lower unit shaft resistance and approximately a 30% lower unit toe resistance than the vibratory installed pile.

These two studies indicate use of vibratory pile installation rather than impact driving will affect the ultimate pile capacity that can be achieved at a given pile penetration depth. Therefore, communication between design and construction personnel should occur, and the influence of vibratory pile installation be evaluated when it is proposed. Impact driving a specific final depth of vibratory installed piles may provide a foundation that meets the engineer’s performance requirements at reduced installation cost."

The references given above are:

Moser, R.L. (1987). Comparison of Axial Capacity of Vibratory Driven Piles to Impact Driven Piles. USAEWES Technical Report ITL-877, 36.

O’Neill, M.W. and Vupulanandan, C. (1989). Laboratory Evaluation of Piles Installed with Vibratory Drivers. NCHRP Report 316, National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C.

 

[PEinc]

Very nice, Panars. Star!

 

[harpoon]

Thanks everyone. I have decided to design piles using values which are inbetween bored and driven piles.

 

[vulcanhammer]

Panars: I recently posted ITL-87-7 at

http://www.vulcanhammer.info/vibro/vibro-technology.php

along with other information on the subject.

http://www.vulcanhammer.net

http://www.vulcanhammer.info

 

[Panars]

Thanks vulcanhammer.