One Dimensional Settlement Calculation Issue

[SciGeo]

Hi all,

My colleague has made a one dimensional settlement estimation and has gone on 6 weeks leave and I cannot get the same result as him but am not confident in my result. Any help on where one I am wrong/right would be great.
We have 2m of sand overlying 1m of clay over rock. Water table is at 0.5m depth. We are adding 2.5m of fill to the site. I am trying to estimate settlement. It is concept design so does not have to be super detailed. Profile Follows:

2.5m Fill to be added to the site (Total Unit weight 20kN/m3)
2.0m Sand (Total Unit weight 19kN/m3)
1m Clay (Total Unit weight 18.2kN/m3), w=28%, Cc=0.6, Cr=0.1, Pre-consolidation Pressure =50kPa
Bedrock

I have attached my working out, I estimated approx 15mm of settlement compared to his estimation of approx 80mm. If someone could let me know if I am correct that would be great. He is much more experienced in this field so I am hesitant to dismiss his calculation.

 

[SciGeo]

I am a Geologist rather than a geotechnical Engineer so I'm sorry if this is an elementary question.

 

[nagatalluri]

SciGeo,

I did the calculation using the data you provided. Seems the settlement you calculated is right. I didn't find anything wrong. May be the other person did not consider the over consolidation into the settlement calculation. That could be the reason for higher number in his case.

NT