an abandoned pit

[v2]

the contractor discovered an abandoned empty pit in the ground as he was excavating for the column foundation.
the pit is about 6 to 8 foot deep and happen to be under the spread footing of the column. the contractor proposed filing up the pit with concrete.
Is this acceptable?

thank you. V2

 

[whyun]

How about filling it with dirt?

 

[Ron]

If it is to be filled with soil, make sure it does not have a hole in it such that raveling could occur. Secondly, it should be penetrated such that drainage can occur (but not raveling).

If the column loads are high, this would create a different bearing condition than the other columns, thus affecting differential settlement. Be careful with that.

If filled with concrete, its unit weight will be tremendously higher than in the past, so watch out for more settlement.

Ideally, the pit would be removed and the area filled with select, engineered fill.

If you must leave in place, consider filling with controlled low strength material (CLSM), a lean concrete mix suitable for this application.

Ron

 

[dougantholz]

v2,
I think that in order to really understand what to do, you need to know what the pit was used for. The use for the site previously, or maybe a couple of tenents ago may tell you what this pit has. Be leary of organics, chemicals & other things. Maybe having the contractor do some exploration around it would tell you if the soil under the box is suitable. Also, Ron had good ideas about perched water. Also I am sure if there are harmful chemicals, you have bigger problems than structural.

 

[LPPE]

Crushed stone works well and is not as heavy as concrete.