A fiber amplifier, such as a rare-earth doped fiber amplifier, includes at least two separate sections of fiber, where residual pump power remaining in one stage of the amplifier is coupled into, and re-used by, the remaining section of fiber. The machine comprises a milling tool to excavate a bench consolidating device, laying device including a feeding duct, and filling device including a tank and injector device to inject a semifluid material, for example concrete, into the bench. 5 times that of the substrate material along at least two axial directions, with one of such axial directions extending substantially perpendicularly to first and second opposed sides of the substrate.