Partial landfill mining

[Geotech_wanderer]

Hello everybody,
the discussion topic that I would like to introduce is that of a partial landfill mining, related to a road that has to cross part of a former urban waste landfill area (the site was closed several years ago). Of course, the area interested by the road must be emptied, since waste does not sustain the loads safely. It is impossibble to change the road path, as well as to build a bridge. Therefore, the issue is to separate more efficiently as possible the part of the landfill to be excavated from the one still remaining as it is. The initial idea was that of doing a slurry wall made of concrete inside the landfill body and then digging out waste in the foreseen road side: some problems with this option are bound to the difficulties to excavate for such a wall in the middle of the landfill body, also because the bentonite would escape from the waste voids, and this would create problems also in the subsequent mined waste classification. Another option could be relying on a reinforced earth slope to be recreated, in order to separate the two parts after waste excavation: anyway, this would probably require to excavate and dispose away a major amount of waste (i.e. more costs). Do you know of some similar cases in which an efficient solution was opted for? Any suggestion would be of great help.

Ps: the waste is not dangerous and well-stabilized.

 

[EireChch]

how long is the road across the landfill? what is the thickness of landfill?

You really want to avoid excavating the existing landfill, can you support the road on a piled slab? Likely expensive but mitigates the cost of disposing of landfill material and the additional environmental warrants required.

You have a tricky problem.

 

[Geotech_wanderer]

EireChch,
thanks for you reply.

The landfill thickness ranges from 2 to 11 m as strictly concerns the waste layer (quite irregular in spacing, but it's an old landfill), plus about 1 m of covering material. The constraints ask for the road to cross the landfill for a lenght of about 150 m. Total excavation foreseen to create a proper road basement would be almost 90 000 cubic meters: half is waste.
Do you know of reference cases of piled slab in situations like this one? Thank you.

ps: under the landfill there is a thick layer of well-graded gravel (at least 10-15 m from the surveys).

 

[dik]

Can you use geotextiles to reinforce the top surface? Can the road be inexpensive with the intent of a limited life?

Dik

 

[BigHarvey]

Dynamic compaction has been used several times for such a case. You can expect the compaction process to lower the Platform about 25% of the waste thickness.