Layered Compaction overlying hydraulic fill
Layered Compaction overlying hydraulic fill
(OP)
Have a query/accusation from one of the contractors on my scheme that I'd apprecaite some opinion on.
Site is an offshore reclaimed island with approx. 20m of hydraulic placed fill (rainbowed by dredger). Ground improvement by vibrocompaction brings that fill up to ~65% relative density. That fill is then topped with 900mm of the same material (dredged carbonate sand, minimal fines content encountered to date)placed in layers to 95% compaction.
second contractor is required to excavate trenches from this reclaimed level and place precast structures amongst other things. he excavates ~2m (so through the layered fill and into hydraulic fill), compacts the trench base to 95% and begins his construction.
second contractor says he is unable to compact the trench base to 95% and is asserting that this is because the hydraulic fill has not been compacted appropriately (~65%RD).
I dont agree with that assertion on two principles:
1. applied compactive effort by second contractor will compact the fill directly underlying even if it means it has only compacted a crust.
2. this work was undertaken without issue on the previous island which is essentially identical (terms of scale and material properties).
My belief is that the contractor is likley to be guilty of one or both of the following:
1. Inappropriate/insufficient compactive effort
2. Using unrepresentative lab MDD value to assess results of in-situ density (sand replacement).
Bit long-winded and i know there will be some further queries but I'm keen to hear others opinions/thoughts.
Cheers in advance
Site is an offshore reclaimed island with approx. 20m of hydraulic placed fill (rainbowed by dredger). Ground improvement by vibrocompaction brings that fill up to ~65% relative density. That fill is then topped with 900mm of the same material (dredged carbonate sand, minimal fines content encountered to date)placed in layers to 95% compaction.
second contractor is required to excavate trenches from this reclaimed level and place precast structures amongst other things. he excavates ~2m (so through the layered fill and into hydraulic fill), compacts the trench base to 95% and begins his construction.
second contractor says he is unable to compact the trench base to 95% and is asserting that this is because the hydraulic fill has not been compacted appropriately (~65%RD).
I dont agree with that assertion on two principles:
1. applied compactive effort by second contractor will compact the fill directly underlying even if it means it has only compacted a crust.
2. this work was undertaken without issue on the previous island which is essentially identical (terms of scale and material properties).
My belief is that the contractor is likley to be guilty of one or both of the following:
1. Inappropriate/insufficient compactive effort
2. Using unrepresentative lab MDD value to assess results of in-situ density (sand replacement).
Bit long-winded and i know there will be some further queries but I'm keen to hear others opinions/thoughts.
Cheers in advance





RE: Layered Compaction overlying hydraulic fill
Independent events are seldomly independent.
RE: Layered Compaction overlying hydraulic fill
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Layered Compaction overlying hydraulic fill
dicksewerrat - unsure the basis of your statements! 'sugar sand', 'not very wise'?! there was me thinking this page was a forum for engineers to help one another, my mistake i didnt realise id walked into the 'i know more than you pi**ing contest'. I await your guidance textbooks on offshore reclamation schemes, oh wise sage!
RE: Layered Compaction overlying hydraulic fill
RE: Layered Compaction overlying hydraulic fill
RE: Layered Compaction overlying hydraulic fill
RE: Layered Compaction overlying hydraulic fill
RE: Layered Compaction overlying hydraulic fill
RE: Layered Compaction overlying hydraulic fill
Hydraulic fill doesn't "crust". It has no cementation and will not bridge...it is elastic and just "bounces".
RE: Layered Compaction overlying hydraulic fill
Independent events are seldomly independent.
RE: Layered Compaction overlying hydraulic fill
oldestguy - apologies, i thought that would have been clear, hopefuly this will clear up what im referring to: http://www.menard-vibro.ae/index.php/pages?path=4_...
BigInch - perhaps you're following my post history or perhaps your guessing but im afraid your wrong regardless as I have moved projects and am dealing with different material than before. This is carbonate predominantly bioclastic sand which is in fact quite the opposite from dune sand being composed of skeletal remains, with weak particles that are prone to crushing, have high inistial void ratio, and highly variable particle size and type. Its a hugely under-analysed material when you consider the amount of construction that has been done on it and with it across the middle east region in the past 15 years. again there are plenty of papers that are slowly closing that gap.I've digressed again!
Ron- I think youve come closest to actually giving me an opinion on the actual issue i raised. My in-situ testing comparison of sand-cone and nuc gauge values should be in later this week. if i can satisfy myself the plant theyre using is appropriate and they are doign the number of passes they say they are and the results come in <95% then I might agree with you! So far, having asked around a few other colleagues the consensus is split but knowing both contractors as i do my suspicion remains with them until proved otherwise!