Settlement Issue with Proposed Building Site on Mine Spoil
Settlement Issue with Proposed Building Site on Mine Spoil
(OP)
I have a proposed building site that is a reclaimed surface mining area and the building is to be placed on approximately 200 feet of mine spoil fill. The fill has been in place since approximately 1992, so it is expected that most of the soil consolidation has already taken place. However, it is still recommended by the geotechnical report to improve the site bearing conditions using a deep dynamic compaction procedure. Upon completion of this procedure the report recommends that shallow foundations may be used with a net allowable bearing capacity of 2ksf. It is also noted that this procedure will only be able to effectively compact approximately the upper 20' of the fill material and therefore, significant differential settlements are expected in the fill below. The report suggests that we design for 1½" of differential settlement over 20'. Myself and the architect for this project do not feel that it is likely feasible to design for this amount of settlement. Has anyone dealt with a similar situation in which it was required for the structure to withstand that much settlement or would it be better to improve the soil conditions further?
Thanks in advance for any advice.
Thanks in advance for any advice.





RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
Mike McCann
MMC Engineering
RE: Settlement Issue with Proposed Building Site on Mine Spoil
It is not a cheap solution. Once you complete dynamic compaction, you can preload the site by placing a stockpile (Say 3 ksf pressure) and install settlement plates so you know when to remove the surcharge. Then remove upper 2B soil depth beneath the slab elevation and place one sack slurry mix. Then design the foundation as isolated footings and connect them to each other with grade beams in x direction, y direction and diagonal directon. Use only 2 ksf bearing pressure and flexible pipe connections. Also make the slab span between grade beams. This will reduce differential settlement but make sure material from 20 to 60 ft is not WOH (weight of hammer) material, i.e. very loose, soft or highly organic.
www.FoundEng.com
RE: Settlement Issue with Proposed Building Site on Mine Spoil
-- Just how big is the footprint of new structure?
-- What type of structure is planned, Wood, Masonry, Steel or Concrete Framed?
-- What is to be the ultimate Use? How important is building/slab straightness?
What is the proposed life-span of the building?
RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
f-d
¡papá gordo ain't no madre flaca!
RE: Settlement Issue with Proposed Building Site on Mine Spoil
RE: Settlement Issue with Proposed Building Site on Mine Spoil
detailed but optimized as to the cost. The building is not tall but it is pretty large, so a number of relatively shallow CPT's would do, possibly completed by a few soil samples to calibrate the correlations and maybe one or two mor expensive tests as dilatometer as fattdad suggests.
In this way you would have a final picture of the soil strenght fluctuations below the building, carry out an estimate of the differential settlements with several foundations options and finally decide which foundation is best with an informed knowledge.
In such a case every additional expense in the foundation structure would be justified as necessary
RE: Settlement Issue with Proposed Building Site on Mine Spoil