The invention relates to a method for monitoring the mechanical behaviour of an subsea pipe (2) carrying pressurised fluids and produced by assembling unitary pipe elements (4), the method comprising a mechanical calibration step that consists in using a measuring cable provided with an optical fibre sensor to measure the deformations in each unitary pipe element when subjected, while ashore, to different mechanical stresses of predetermined directions and intensities, and, on the basis of these measurements, establishing the mechanical signature of each unitary pipe element; and a monitoring step consisting in using a measuring cable (18) provided with a fibre optic sensor using Brillouin backscattering and positioned in the shape of a helix with a constant pitch (p) on each unitary pipe element, the direction of the pitch of the helix alternating in two adjacent unitary pipe elements, to recover the variations of the optical signal injected in the sensors when the pipe is in service, and, from the variations of the signal and the mechanical signature of each unitary pipe element, determining the stresses that each unitary pipe element is subjected to.