A testing method for measuring the unloading strength of a fractured rock comprises the following steps that firstly, core boring sampling is performed on a rock
mass, a deformation
measurement device is installed on a test piece, and the test piece is placed in a tri-axial test cylinder; secondly, the
axial displacement of the test piece keeps unchanged, confining pressure is exerted to reach a design value, afterwards, the confining pressure keeps unchanged,
axial pressure is exerted to reach a design value; thirdly, the
axial displacement of the test piece keeps unchanged, the confining pressure is decreased gradually according to a design unloading rate until the confining pressure reaches an
axial pressure sudden-
change control point, and the
axial pressure and the confining pressure, corresponding to the sudden-
change control point, of the test piece are recorded; fourthly, the
axial displacement of the test piece keeps unchanged, the confining pressure is restored to an initial design value according to a design
loading rate, afterwards, the confining pressure keeps unchanged again, and the axial displacement of the test piece is increased to the next design value according to the design
loading rate; fifthly, the processes of unloading fracture, confining pressure restoration and axial
pressure increase are repeated, the unloading fracture strengths of the axial pressure sudden-change point, corresponding to different confining pressures, of the test piece are obtained; sixthly, the mechanical parameters of the unloading facture strengths are obtained through data fitting.