In order to express the behaviour of fractured rock in compaction test with a constitutive equation, some basic discussions were attempted. The variable-compliance-type constitutive equation was employed in this study. The constitutive equation can express the failure process of rock, which has been well proved heretofore. In the constitutive equation, it is assumed that the rock fails at a rate which depends on stress severity.
In this study, the concept of stress severity Sv was expanded to the stress state where Sv took negative value and healing parameter Hp = -Sv was introduced. The constitutive equation was also modified assuming that fractured rock is gradually compacted or healed at a rate which depends on healing parameter. According to the results in this study, it can be said that the equation expresses the behaviour of the fractured rock when the compliance becomes smaller in the compaction test. In addition, to some extent, it was also possible to explain the increase of the principal stresses with time. Though further discussions are essential in the future definitely, it can be said that the modified variable-compliance-type constitutive equation showed much potential for simulating the behaviour of fractured rock in compaction test and interpreting strength recovery of rock in loosen zone or EDZ around an underground structure.