Mad Mike
Geotechnical
- Sep 26, 2016
- 220
I've recently been tasked with providing a compaction specification for carbonaceous shale which is to be used in the engineering of large-scale industrial cut-to-fill platforms.
The shale is a grey to dark grey micaceous material recovered as platelets; sometimes hard but non-durable - the volumes being moved are a couple of million cubic metres.
The common specification for compaction of shale is to restrict the layer thickness to 8" and use very heavy compaction plant; however there is also a general caution against the over-compaction of shale fill, which may heave in response.
Question is, when I'm dealing with the construction of high fill embankments, where I'm worried that under-compaction of the shale could lead to excessive settlements, should I be worried about over-compaction and heave of the fills? My intention is to specify a layer compaction of 95% Mod. AASHTO in 8" lifts.
I'm aware in principle that there may be some heaving of the upper fill material; which I would expect to be less significant than the settlement in a high fill embankment (30 to 50 feet fill thickness). However in areas where the fill is relatively thin, say 10 to 20 feet, I'm concerned about heave if the shales are over-compacted. There is no frost in my area.
How does one design around this, short of zoning the fills with different compaction specifications for each zone?
I'd greatly appreciate any direction or case histories.
Mike
The shale is a grey to dark grey micaceous material recovered as platelets; sometimes hard but non-durable - the volumes being moved are a couple of million cubic metres.
The common specification for compaction of shale is to restrict the layer thickness to 8" and use very heavy compaction plant; however there is also a general caution against the over-compaction of shale fill, which may heave in response.
Question is, when I'm dealing with the construction of high fill embankments, where I'm worried that under-compaction of the shale could lead to excessive settlements, should I be worried about over-compaction and heave of the fills? My intention is to specify a layer compaction of 95% Mod. AASHTO in 8" lifts.
I'm aware in principle that there may be some heaving of the upper fill material; which I would expect to be less significant than the settlement in a high fill embankment (30 to 50 feet fill thickness). However in areas where the fill is relatively thin, say 10 to 20 feet, I'm concerned about heave if the shales are over-compacted. There is no frost in my area.
How does one design around this, short of zoning the fills with different compaction specifications for each zone?
I'd greatly appreciate any direction or case histories.
Mike