To overcome the limitation of the existing three-dimensional swelling constitutive model

the swelling tests under lateral restraint condition are conducted on the swelling rock sampled from a water-rich argillaceous slate tunnel. On the basis of the experimental results

the relationship between the axial swelling ratio under lateral restraint and the water absorption time is revised

and a one-dimensional constitutive equation for swelling is developed. Based on the Kinnick conditions

the overall swelling process is described with considering the contribution of the maximum and minimum swelling stress to the swelling behavior. With the time of the maximum volume swelling rate being the critical time

a time-dependent 3-D swelling constitutive model of argillaceous slate is developed

which can be expressed stage by stage. The results show that the relationship of axial stress and axial swelling rate can be expressed as a negative logarithmic function. When the water absorption time is less than or equal to the critical time

the relationship between the lateral restraint swelling ratio and the water absorption time follows an exponential law

and the volume swelling rate obeys the three-dimensional swelling constitutive model with considering the time effect. When the water absorption time exceeds the critical time

the axial swelling ratio under lateral restraints no longer changes with time

but remains to be the final axial swelling rate under lateral restraint. Moreover

the volume swelling rate no longer obeys the constitutive model

but becomes the constant value (the maximum volume expansion rate). These results can provide a theoretical reference for solving the surrounding rock swelling problem of water-rich soft rock tunnel.