Deep Soil Mixing - Secondary Compression

[RGKVI]

Im designing deep Soil/ cement mixed columns (1.5m diameter) 12m deep at 2.8m centres in fibrous peat. Loading from a 10m x 10m raft foundation is 120kPa (SLS). My question is will the fibrous peat between the columns undergo secondary compression or will the adhesion between the peat and the mixed columns mitigate secondary compression and enable the columns and peat to achieve a combined stiffness to resist settlement.

 

[GeoPaveTraffic]

I have never done a project like you are describing, but my first impression is that the soil/cement columns will take 100% of the load and transfer it to the base of the columns. This assumes that the columns penetrate through the columns and bear in a compentent soil/rock strata.

Over time, the peat will compress/degrade causing the peat to settle away from the base of the raft foundation. In fact as the peat compresses it will like cause additional load on the columns.

Again, the above thoughts are just "off the cuff", but you really need to think this through as there is a lot going on here.

Mike Lambert

 

[RGKVI]

The design guide I use is EuroSoilStab 2002. I've designed soil cement columns in Tidal Flat deposits (Cu=10kPa) before. The method is based in a combined soil stiffness and differs totally from pile design. The only difference here is Peat suffers from secondary compression ie increase in compression without an increase in stress. I was wondering if secondary compression would be mitigated by mixing stiff columns insitu.