Abstract: Under traffic loads, the magnitudes and directions of the principal stresses applied in the soil elements of soft subgrade change simultaneously. Namely, as the shear stress changes in amplitudes, the principal stress axes continuously rotate. For this problem, a series of undrained long-term (10000 cycles) cyclic torsional tests on the natural Wenzhou soft clay after K₀ consolidation are conducted using the GDS hollow cylinder apparatus. The deformation behavior of the K₀-consolidated natural Wenzhou soft clay under different dynamic stress levels considering the rotation of the principal stress axes thereby is analyzed. The test results show that the rotation of the principal stress axes causes a higher pore pressure in the soil and an extra strain in the vertical. Besides, with the equidifferent increase of the torsional shear stress, the increments in both vertical strain and pore pressure grow up gradually. Considering the diversity of deformation development pattern of K₀-consolidated soft clay under different dynamic stress levels considering the rotation of the principal stress axes, the shakedown theory is utilized. Thus, the scopes of the critical dynamic stress levels, namely the threshold cyclic stress ratio, the allowable cyclic stress ratio and the critical cyclic stress ratio of K₀-consolidated soft clay considering the rotation of the principal stress axes are determined. It is proposed that the allowable cyclic stress ratio should be the criterion of settlement control for road engineering. Compared with the results of triaxial tests, when considering the rotation of principal stress axes, the control of dynamic stress in road engineering should be stricter.