The undrained unloading tests of isotropic consolidation on soft dredger fill of Tianjin Binhai are performed using the stress-path triaxial apparatus to determine the effects of different unloading stress paths and unloading rates on stress-strain relationship

pore pressure variation and failure strength characteristics. Some findings are as follows. The stress-strain curves under each unloading path are approximately hyperbolic curves. Under the unloading stress path of UU0.0(radial unloading

axial not unloading)

the deformation of samples exhibits axial compression

and the curves of pore pressure have sharp yield points. On the contrary

the deformation of samples under the path of UU2.0(both axial and radial unloading)

UU∞(axial unloading

radial not unloading) and UL1.0(axial unloading

radial loading) show axial tension. In this way

the pore pressure increases with the increase of strain

and finally the growth rate of the pore pressure slows down and tends to increase steadily. Under the same stress paths

the larger the unloading rate

the slower the development of the pore pressure in the initial stage of unloading and the greater the peak pore pressure. The stress-strain curves at unloading rate of 0.1

0.2 and 0.3 kPa/min are found that the initial tangent modulus is greatly affected by unloading rate under unloading compression paths

while it is not influenced under the tensile paths. The value of unloading failure strength is the maximum under the UL1.0 path

the minimum in the UU2.0 path

and centered in the UU∞ path. Under the same unloading path

the failure strength increases with the increase of the unloading rate. According to the normalization of stress-strain curves

the formulas

which considers the influence of unloading rates and unloading stress paths

are developed to estimate the initial tangent modulus and the unloading failure intensity.