Determination of boundary stress by using Casagrande graphical method is labour-consuming and some difficulties are connected with visual evaluating the shape of soil deformation experimental curve. The programme for computing boundary stresses was designed on the basis of Lotus 123 calculation sheet to eliminate mentioned difficulties. The programme is based on evaluating the run of curve using absolute values of curvature index calculated from the difference of left-sided differential quotients. Presented procedure enables processing the series of measured values recorded at ASCII form. Model was verified experimentally by using the test where boundary stresses were determined in uniaxially deformed soil samples. Model soil samples consisted of the mass of loose soil aggregates 1-8 mm diameter, were put into rigid steel cylinders 80 mm diameter and compacted at 200 kPa pressure. Soil of heavy clay mechanical structure was used in the experiment. The results confirmed correctness of developed model and its usability for computing boundary stresses.