In-situ Horizontal stress calculation from Pressuremeter test data

[Geosubhtech]

Greetings to All,

For pressuremeter test (prebored pressuremeter test) interpretation (undrianed shear strength) the reference state has been taken as horizontal earth pressure (P₀) at that test depth for all strain calculations. This is the basic assumption taken by A.C. Palmer (1972), Ladanyi (1972). Who gave the mathematical expressions for calculation of undrained shear strength of clay, as slope of corrected pressure vs. Ln(del v / V).(I will attach these papers if anyone wants to read.)

del V = V(measured)- V (at P₀ )
V = probe core volume + measured Volume at P₀ + del V

So, here my doubt is in my calculation of P₀ if am following iteration method given by A. MARSLAND AND M. F. RANDOLPH (1977) i am getting a P₀ of 2368 kPa and undrained shear strength of 557 kPa at a depth of 30 meter depth.

But if i will take simple starting point of thr elastic linier portion P₀ will be 590kPa and undrained shear strength of 825 kPa.

So, please guide me how can i fix the reference volume so i can correct shear strength of the soil and how to ensure the P₀ values were reasonable.

I am attaching the curves below. If you need anymore info please reply below.

Many many thanks for your concern.