Road Construction in Black cotton soil 1

[ayyaz26]

I am working in sudan and we plan to construct Gravel road in Malakal area through labor intensive techniques.The problem is that the subgrade in this area is black cotton soil .I wanted to know what techniques we can apply for compaction of this soil

 

[fattdad]

Never heard of "Black Cotton Soil" - any further information? Also, where's the ground water table?

f-d

¡papá gordo ain’t no madre flaca!

 

[sammyk]

Never worked with the stuff myself but I asked some of the "overseas" engineers at the office about it.
Black Cotton swells in wet conditions and then contracts and forms huge cracks in the dry seasons.
Black Cotton Soil has lots of clay in it. Try Lime stabilization with a geo-grid. This will allow the stabilized sub-grade to "float" over the highly unstable natural soils beneath.

 

[cvg]

given that the material is very moisture sensative, proper drainage to keep the subgrade from saturating and to help it drain quickly will be just as important as the initial compaction

 

[ayyaz26]

Thanks to all for their valuable advice

 

[fattdad]

How thick will your roadway embankment be? If you are placing a thick fill over this stuff, then that may "insulate" it from the moisture changes it currently sees and as a result dramatically reduce the shrink-swell tendencies.

Just a thought. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[ayyaz26]

I am considering to have embankment layer 0f 30 cm and then a grave material (subbase layer) of 20 cm.It may isulate the water but the real problem will be from sides seepage which will undermine and damage the road

 

[cvg]

side seepage is a concern unless you can keep your ditches away from the edge of the road. Also, unless your embankment is imported material with low plasticity, the gravel will allow water right through to the embankment layer which will swell. Putting a good cross slope on the road will help to drain water off the top faster and reduce the amount of water reaching the embankment or subgrade

 

[defg]

Yes there's a lot of ways can be used to combat effect of road constructed on blackcotton subgrades.These are:
-Realignment of the road around the deposits
-Excavation of the clays and replacement with non-expansive backfill materials
-Limiting expansion of the clays by placement of surcharges of non-expansive fills over these deposits
-Precluding variations in moisture content of these clays so that the soils do not undergo alternate cycles of expansion and contraction
-Treatment of the clays with lime and/or cement which reacts with the clay minerals to produce stable compounds which are affected by moisture content changes and
-Utilization of geotextiles to isolate pavement layers from the expansive subgrade.You can choose on of the above said method to solve your problem.

 

[mudman54]

i think there is something about black cotton soil in ray yong's book titled soil behavior