Soil Replacemet (Shallow Foundation on Backfill Located on Mining)

[salman85]

Hi Everyone,

I have conveyor foundation with 75 KPa structure bearing pressure (deliberate designed with less structure bearing pressure), it will stand on the embankment mining soil which is backfill and compaction not follow common procedure (backfill and compaction should be 25cm per layer, but mining adopt 1m per layer and no compaction, just dumping and passed with Hauling Dumptruck).
The only data i have is SPT (only old backfill and for the new backfill 3-7meter not recorded in SPT)..if i look at the way backfill & compaction in mining, it is horrible about settlement issue..
Client guarantee for upper layer soil with 200Kpa ultimate bearing capacity

Can i used SPT data and some of assumption due to new backfill to analyse settlement? most of soil composition is cohessive with firm upto stiff consistency.It is understood when we try to analyse settlement, condition of soil wheather normal consolidated or overconsolidated is important thing.

What the conservative way to analyse settlement between assuming normal consolidated or underconsolidated or overconsolidated?

Do i need soil replacement to reduce the value of settlement? i have silty sand as soil replacement to be use for other structure.

another test in situ, i use DCP test before and during earthwork..Refer to another threads in this forum about DCP test correlated with undrained shear strength and then convert to CBR and finally ultimate bearing capacity.

 

[GeoPaveTraffic]

If I understand your post, you have no data on the 7 meters of new fill that the conveyor foundation will bear in. If this is the case, then you can not analize or even guess at the amount of settlement that will occur.

The good news is, generally conveyors are not particularly settlement sensitive. Options include:
1) performing additional explorations and testing to get data with which to perform the analysis,
2) building the conveyor and making periodic adjustments as the settlment becomes a problem, and
3) remove the fill and place properly compacted fill.

Good luck.

Mike Lambert

 

[salman85]

Thanks GeoPaveTraffic,

Yesterday, i try to DCP test (hammer 8kg, hammer drop 600mm, cone dia.16mm and 60 degree cone angle), here is the result :

Blows Penetration (mm)
4 100
6 200
5 300
6 400
5 500
4 600
10 700
25 800
42 900
68 1000

Cannot reach more than 1000mm seems like hard enough or hit boulder,
try another location, plus minus the same as above.

How about it?
anyway, thanks for your advice, i really appreciate it