Long Term Deformation Rockfill

[rocfill]

Hi Everyone,

Long time reader, first time poster here. I'm hoping I can tap into the massive amount of experience on this board.

Background:
I'm currently conducting settlement analysis for a shallow foundation (maximum applied pressure of about 50-60 PSI). The foundation will be founded on fill, native sand and gravel and/or bedrock, in descending order. The fill will be a well graded durable rockfill (4" to 8" max particle size) with trace fines produced from a quarry/crushing plant. The fill thickness will be up to 45 feet. The in-tact rock strength of the quarry rock is strong to medium strong. A method spec is in place which would see the rockfill placed in loose lifts of up to 16" and compacted with 8 to 10 of passes with a vibratory roller.

I have a number of papers which research the long term deformation of rockfills used in dam construction. I think this is well documented and I think I understand the mechanisms behind these settlements. However, in my case, I do not have the relatively high in-situ stress commonly associated with some of the dam settlement case studies (no pun intended).

Questions:
Assuming good construction practices, would you be concerned about long term settlement of the rockfill described above? What would you say if the differential settlement criteria was extremely low (<1/4" over 25')? Does anyone have previous experience with the long term performance of a similar fill?

Thanks in advance.

 

[Geostructsparks]

Most geotechnical papers on rockfill are for earth dams which are poorly-compacted, therefore may not be much use. South of Reno, a contractor constructed a 150-foot high fill across a canyon, including 3/4H:1V MSE slope reinforcement, to support falsework for the Galena Creek arch bridge (oxblue has a webcam). It was well compacted, don't know exactly how much (NDOT monitored, not my firm, appears to have been well-compacted, 12" minus to soil-sized, low-plasticity fines) however after 1 year there was only about 3/4 inch. I imagine that it is still continuing at that slow rate.

 

[casimmons]

Sounds like pretty heavy loads for fill (50 psi=7200 psf) and strict settlement criteria. What structures will be supported by this rock fill? Full scale load testing and settlement monitoring would be a good start. I don't know if your loading/settlement criteria is achievable with shallow foundations.