Abstract：Cambridge self-boring pressuremeter(SBPM) is used in this test to study the stress and strain of the clay adjacent to the expanded cavity wall. Self-boring pressuremeter is a cylindrical device designed to apply uniform pressure to the wall of a borehole by means of a flexible membrane. Both pressure and deformation at the cavity expansion are under the assumptions that the probe is expanded in plain strain，undrained，axially symmetric about the pressuremeter and in elastic-perfectly plastic material. Based on the hypothesis，theoretical stress path is deduced；and comparison between the theoretical stress path and experimental one has been made. The results show that in the plastic phase，the theoretical stress path corresponds well with the experimental one，while in the elastic phase，the correspondence is less satisfactory. Comparison between the theoretical curves deduced by nonlinear and linear analysis with the experimental ones indicates that nonlinear analysis fits well with the actual behaviour of clay. Besides，according to the curve of stress path，variety of stress in the clay is analyzed；stress history of the clay is determined；and some parameters of the clay are deduced.
