Construction on old mine tailings

[GilBor]

I am trying to decide about the purchase of a land property (5000 M^2)
located in an area used by a mining company to dump tailings
about 50 yrs ago. I hired a soil engineer to help me make the decision
and am seeking farther advice (second opinion) from the experts in
this forum. Details follow.

The property is located in Guanajuato (Mexico). The tailings were
layered on a slope of a hill, forming a big flat terrace sized about
200 by 100 meter. The soil is mostly fine powder, with some thin layer
of top soil (max 30cm) with some vegetation (trees up to 3 meters
high). I intend to use this land to construct 3 brick houses (for
myself and 2 friends). A soil engineer from a nearby university, who
also works as a consultant for foundations, looked at it, took some
superficial samples (the owners wouldnt let us make holes deeper then
1 meter) and is supposed to send me a lab report within several days
with recommendations for foundations. He said I will probably need to
build the house on a concrete slab located on top of a treated layer
of imported material (soil moved from some other site, i guess).

Specific questions:

1. Is it reasonable to build a (modest) house on such a soil? I mean,
can you make not-too-expensive foundations that will support the house
for many yrs?

2. In case the answer is yes, is the aformentioned method the right one
or I should look into other methods?

 

[boo1]

Think about the investment vs risk, weight the options. Appears to be a moderate to high risk.

I have built on a few sites were it would have been cheaper to just buy a better building lot.

Why risk your investment on a home on a questionable site?

 

[Robert168]

Although my posting was deleted, I would like to post again to express my concern aboutn the stability of the tailing itself. It seems that on one cares about that the tailing is on the slope of a hill.

 

[BigH]

Robert168: I alluded to it (quietly) in my Oct28 post - How close is the site to the face of the dam? There was Gilbor's response - seems that his site borders the dam face but that the site is so big, he is planning on building near the back where the "natural ground" is fairly shallow. With 100m of so between house and face of dam, I doubt there is much concern unless the dam is extremely high - but your point is one that is well taken and perhaps I or others should have put more effort and thought into it! In these cases, though, the coarse materials will have fallen out near the face so that at least we have some "good" material in the immediate vicinity. One of the important factors to consider is the groundwater regime in the tailings area.

Sometimes, in the threads, the discussions seem to flow like water - many times away from a number of salient and important points. It is imperative for someone (like you), in the middle of the thread, to point out the various factors and concerns that the "flowing water" didn't pick up. Thanks for keeping all of us on our toes.