MH embankment fill for trains?

[AK92]

Hi,

The client wants to use a MH (USCS classification) type material for an embankment. 99% of the material is silt/clay. LL is 78%, PL is 54%. MDD for modified proctor test is only 1.22g/cm3 with a OMC = 41%. The embankment is going to be constructed on soft soils, so there will be wick drains installed using surcharge and staged construction with basal reinforcement. I'm not too worried about the settlement beneath the fill as that's going to be taken care of by the wick drains and surcharge, but the settlement of the fill itself. I've read that post-compaction settlement of an MH fill is likely to be 2%-4%. For a 6m fill, this is going to be 120mm - 240mm under selfweight which is way more than what is acceptable if it is long-term. Also, how would I assess the settlement of the fill itself under heavy trains loading? Bearing capacity of the fill itself is also an issue here.

 

[BigH]

This material would not be acceptable in India based on their national standards. I know you are not in India - but it is a reference. The train loading would be transient but the settlement of the embankment under self weight is going to happen. There are references that permit estimations of settlement under self weight - but as with any consolidation settlement, they are estimates. One way I thought of in the past is to lay wick drains horizontally in the fill as you construct it - shortens the drainage path for quicker settlement; place a preload on for as long as you can, remove and you should have built out much of the self-weight settlement prior to the laying of the tracks.

 

[AK92]

@BigH

Strangely enough, the CBR test at 100% is 17 and for 95%, 8.9, which seems to be rather high? I'm now a bit curious on how the material will behave. Interesting idea on laying PVD's horizontally!