Suction measurements for estimating in situ effective stress

The vertical and horizontal total stresses and the pore water pressure combine on an element of soil in the ground profile to give the in-situ effective stress. When the same element of soil is removed from the ground in the form of a sample the vertical and horizontal total stresses reduce to zero. However, the sample retains a pore water pressure but its value is negative because of the unloading that has taken place.
 
If the extracted sample is (a) saturated, (b) removed from the ground without allowing it to change in volume, (c) at its in-situ water content and (d) free from disturbance, the measured suction in the sample can be used to estimate the in-situ stress condition. Moreover, if a value for the vertical effective stress is assumed, it is possible to calculate the radial effective stress and hence the value of K₀.

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