Abstract: The developed flexible uniform pressure loading device and traditional rigid loading device are applied to large-scale geomechanical model test, of which loading effect is comparatively analyzed by using the stress nonuniformity coefficient ?. The test results show that, with the loading stress and the distance from the surface increasing, the stress nonuniformity coefficient ? decreases, and stress distribution tends to uniform. Comparing to the rigid loading method, flexible uniform pressure loading device is more beneficial to uniform stress dispersion and forming uniform stress field. With the flexible uniform pressure loading device being applied to the test, the stress field is nearly uniform where the depth from the surface is 300 mm in the test condition; and the ? is 0.086 when the initial stress has been applied; and the corresponding ? is 0.283 with rigid loading method applied in the test. Even though the distance from the surface is short or the loading stress is low, the flexible uniform pressure loading device also produces a good uniform loading effect, and when the on-load pressure is 0.28 MPa, the ? is only 0.174 where the depth from the surface is 150 mm. The device has the function of reducing range of boundary effect and improving model test accuracy.

Key words: rigid loading, flexible uniform pressure loading device, model test, stress nonuniformity coefficient, comparative analysis