Meaningful empirical correlation between Su and Phi in cohesive silty clay soils 1

[Raglangeo]

Can anyone point me towards work that has been done on this please

 

[GeoPaveTraffic]

There are NO meaningful correlations between Su and Phi. These properties are not related, period.

Mike Lambert

 

[geotechguy1]

What tests are you getting Su or Phi from?

 

[GeoPaveTraffic]

Below are for fine grained plastic soils.
My preference in order of reliability for Su:
1. Unconsolidated undrained triaxial
2. Unconfined compression
3. In-situ vane shear
4. Mini vane shear
5. Pocket Penotometer
6. SPT blow count coorelation

My preference in order of reliability for Phi:
1. Consolidated undrained with pore water pressure measurements traixial
2. Consolidated drained triaxial
3. Fully softened correlation based on phi and clay fraction
4. Peak phi based on plasticity index


Mike Lambert

 

[geomane]

Su is affected by moisture content, the effective friction angle is not

 

[EireChch]

People bash SPT to Su correlations a lot. I agree there is some issues but I have always found them to be reasonable, in cohesive material which is stronger than firm ~50kPa plus.

Likely an unpopular opinion, but I would put SPT correlation above PP and mini shear vane!!! I dont do many PP or MSV so maybe I dont have enough information....

 

[GeoPaveTraffic]

EireChch,

I agree SPT, PP, mini torvanes all have their problems. In some soils one is better than the others, in other soils the ranking switches. Really depends on teh soils and, in the case of the PP and mini torvanes it depends on who is running the test.

Mike Lambert