Mohr envelope for overconsolidated soil :common Yet puzzling

[MCC1966]

Triaxial (consolidated-undrained) under the confining stresses (sigma3) show (note that 15% is the failure criterion according to ASTM standard):

sigma3 axial strain sigma1-sigma3 pore p
20 15 289.772839 -87.31215224
50 15.00151 172.5743 -15.5049
100 15.00212432 106.3252557 45.87678529

I want to get the total strength parameters phi and c for this overconsolidated soil. However, when drowing Mohr circles I'am getting a circle completely inside a circle.(try it if you do not beleive) How can I get the Mohr envelope in this case?

 

[BigH]

Keep in mind for HOC soils that with equalization of pore pressures (i.e., sucking in of water), they will be weaker than initially. - Look at the stress paths for HOC and NC/LOC. The latter curves are to the left of the drained stress path; the HOC is to the right - equalization is always to the drained line.

 

[MCC1966]

I have been able to know that this soil is sandy soil. The only justification for such results is that the sample subject to 20 KPa (highly dilative) confining stress is denser than the one subject to 50 KPa (lightly dilative) which is in turn denser than 100 KPa (contractive).
They are from the same soil but with different state parameters (e,P') it is common situation but assigning shearing strength through Mohr circle is not possible in this case. Shearing strength through Mohr Coulomb circle should be considered for soils having the same moisture contents (void ratios) ..should not it ? please answer me
The Dilative soils will have strain-stress curve continously hardening so it is better to look at the stress path curve and the points having minimum P' and drow the best line fitting them to get the strength parmateres that will be transfered to Mohr Coulomb strength parameters.
NOw if the stress paths for these samples do not experience decrease in P' then one has no choice but to choose a specific level of strain E =15% (ASTM standard) to get the strength parameters at
Do you guys agree with me