Sand and gravels ground replacement
Sand and gravels ground replacement
(OP)
Hi,
sorry for such a long post!
We have been replacing 20000m3 of peat and soft silt below of the footprint of a 8 m high embankment with well graded sands and gravels, (we replaced down to a layer of sand and gravel also)
The depth of replacement varies 1 - 6m, and the level of ground water is 2-3 m below OGL made it impossible to compact with roller. (quick water ingress when we reached the gravelly layers). The area will flood when the rains come.
The good grading and cleaness of the gravels give very good appearance to the job, and the loaded dumpers cause no rutting at all.
We are unsure whether the lack of compaction during the laying of the gravels (just pushed them into the hole with a dozer) may mean that we need to vibrocompact or use other technique to consolidate the sands and gravels or we should just build up the embankment and check the settlements. This we have to do it anyway, but we would hate to find out that this settlement is very slow..
Somebody suggested Dyamic penetrometer testing to check the whole 1 to 6 m sands and gravels we layed.
What do you think?
sorry for such a long post!
We have been replacing 20000m3 of peat and soft silt below of the footprint of a 8 m high embankment with well graded sands and gravels, (we replaced down to a layer of sand and gravel also)
The depth of replacement varies 1 - 6m, and the level of ground water is 2-3 m below OGL made it impossible to compact with roller. (quick water ingress when we reached the gravelly layers). The area will flood when the rains come.
The good grading and cleaness of the gravels give very good appearance to the job, and the loaded dumpers cause no rutting at all.
We are unsure whether the lack of compaction during the laying of the gravels (just pushed them into the hole with a dozer) may mean that we need to vibrocompact or use other technique to consolidate the sands and gravels or we should just build up the embankment and check the settlements. This we have to do it anyway, but we would hate to find out that this settlement is very slow..
Somebody suggested Dyamic penetrometer testing to check the whole 1 to 6 m sands and gravels we layed.
What do you think?





RE: Sand and gravels ground replacement
RE: Sand and gravels ground replacement
RE: Sand and gravels ground replacement
Did you say you were using a roller? And trucks were not rutting? If you weren't, then you could definitely expect settlement, as fill goes in (under dozer pressure) at about 88% compaction, way below what you want for a roadway certainly. If you did just dump it in the hole, I would forget our advice and just hire a geotechnical engineer. He/she could give you settlement numbers from drill rig logs and would be able to tell you just how long it's going to take to settle. Good luck.
RE: Sand and gravels ground replacement
Further, I would presume that the abutments are piled? The fill might have some downdrag loading on the piles that you want to consider as well.
I would suggest that if you have the time, when you reach the top layer of the embankment fill to add another 2 m or so of fill for, say, 20 m behind the abutment and let it sit for as long as possible. This would effectively preload to some extent the materials so that on the preload fill removal, any settlement that might occur would have had at least a reasonable portion of it already induced. Highway construction - if you time things right, should be able to give you several months of preload before you have to remove it. Just a few thoughts that you should consider.
RE: Sand and gravels ground replacement
We do have geotechnical engineers. Their advice is to start building the embankment and monitor the settlement. They expect very little settlement because the material used to backfill has very good continuos grading.
But this kind of ground replacement is usually done with rock over here, so they dont have experience doing this with sands and gravels.
I was thinking in doing what BigH suggest, not spend money in vibrocompaction and surcharge the embankment and monitor settlement.
My fear is that the settlement being slow, we cant afford waiting too long...
The DPM testing they recommended me is not exactly DCP, is similar but it is done with a 30 kg cone, I suspect that will not be handheld!!
I was hoping someone here had some experience with this DPM or in vibroflotation/vibrocompaction.
RE: Sand and gravels ground replacement
So now the profile is
an avg of 3/4/5 meters of uncompacted gravels
--- 2/3 of naturally compacted sands and gravels
-- limestone rock.
The abutments are piled, probably because designers having rock only 8-9 meters deep they wont allow us direct foundation on the gravels. (the design is not closed).
Thanks for your input.
RE: Sand and gravels ground replacement
i guess i'm kind of asking the question now but it seems relevant to jomando's situation. any opinions about my thoughts? (i might be way off based on what little i know about the actual conditions)
RE: Sand and gravels ground replacement
From that experience, I'd figure the bridge soils in the lower depth of your embankment are fairly stable. If the peat is removed and you have good frictional granular soils placed and you are then able to develop a subgrade for subsequent compaction, you are doing well. I'd follow that with a series of borings (or dilatometer soundings) to gauge the soil strength/modulus value and then evaluate the long-term performance. I'd vote that it's all going to work out just fine for an embankment. Where you have to be most careful is on the edges where an embankment slope failure could develop.
f-d
¡papá gordo ain’t no madre flaca!