settlement of clay fill

[henders1]

looking for information on typical settlement of recompacted stiff sandy clay fill to be used as a structural platform for industrial buildings. columns likely to be piled, but ground bearing floor slabs will be used if posible. anyone have any case studies on what magnitude of settlement might be expected from self weight component of about 8m height of fill

 

[jdonville]

henders,

See NAVFAC DM7-1 or 7-2 - There is a table with ranges of long-term self-weight settlements for various fill materials.

These are available on

http://www.vulcanhammer.net

Jeff

 

[Zambo]

I think you will find it difficult to fill 8m with a sandy clay material and then construct a ground bearing slab on it. I am sure you will, at least, need a substantial layer of good subbase material.

How many storeys? Has driven concrete piles for the slab already been found to be uneconomic?

 

[BigH]

Don't think I would put floor slab on 8 m of clayey fill. Probably would be best to install some stone columns in the fill after it has been placed - or other inclusions. This will stiffen up the fill and present less chance for settlement. A number I heard years ago for clayey fill was about 1.5% or so - for 8 m this would be 100 mm or so - too much.

 

[fattdad]

I would not think twice about putting a ground-supported slab on 20 ft of sandy lean clay fill. I would insist on proper subgrade preparation, proper compaction control and settlement plates after earthfill was completed. I would document post-placement deformation of the fill and proceed with construction after 3 weeks of stable elevation shots.

The compressability of clay fill is also related to the compaction moisture content. If you can place the clay on the dry side of optimum you will further limit post-placement deformation.

Hope this provides futher insight.

f-d

¡papá gordo ain’t no madre flaca!

 

[henders1]

Thanks for the responses so far, these are very useful. Hadn’t seen that NAVFAC book before. The site in question is for an industrial estate and the exact loadings are not known at this stage. I expect that there will be steel portal frame structures with a floor slab, ground bearing if possible. The clay fill is quite sandy ( a glacial till or boulder clay), but from the posts and from a bit of literature searching i am expecting some internal settlement (saw a figure of 0.5% x fill height for 1 log cycle of time in a BRE report 2003).The options for the floor seem to be build straight on the clay fill, place a granular capping on the fill and build on that, stone columns or piling. I quite like the idea of using stone columns as from previous experience they take away a lot of the risk for a limited cost. I know of a few structures in the UK where recompacted boulder clays have been used, but ive not managed to lay my hands on any post construction settlement data. If its anywhere near the 1.5% fill height then I think I will need to forget it as the building columns will probably be piled and that’s a lot of differential movement. If compaction is good then maybe it would be do-able, but not convinced that a boulder clay can be compacted that well. any other thoughts on risk mitigation ?

 

[TexasGeotech]

NAVFAC 7.2 lists compression of fill based on soil type (1.1 to 2.5% of fill height for a CL to SC soil), but I am not sure where they got these values. It states these are for Standard Proctor level of compaction and the lower values are for 2800 psf surcharge and the higher values are for 7200 psf surcharge (fill above subject layer). There is an embankment of CL in Ft Worth that settled 0.7%, and a highway embankment of SC in Austin that settled 1.0% but some minor settlement was due to compression of the underlying stiff clay. I think 0.5% is a good estimate for a properly compacted CL/SC, but I would design for (anticipate) 1.0%.

 

[dirtsqueezer]

Just a newbie here, but if the fill is to be compacted, expecially to a good modified proctor, but even a standard, wouldn't the settlement be determined not by whether it's clay or not, but how it compares with the values reached in the lab?If it compacts in the lab, and if you were to specify 95% mod(which in my experience is rare for the depth of compacted fill), wouldn't settlement be minimized? You could also predict how your fill will compact by comparing the in-situ moisture to your moisture-density curve and see what the max compaction will be. If it's lower than your percentage specified, you will need to improve the soil, or since it's already being dug out, import the rest of the fill; probably more expensive.

That being said, if it's clay, beware of placing in wet weather. It will go south in a hurry, and is not easily dried out.

Input on this post would be appreciated. Thanks.