almost all gas turbine/comressor packages are split shaft design. In a continious shaft design, there is a single power train shaft that starts at the air compressor, thogh the burnrer section on the the air compressor power turbine and then to the take off power turbines.
The split shaft design has the shaft starting at the air compressor, through the burner and on to the air compressor turbine section. A second shaft has only the take of power turines on it and there is an "air gap" between the two shafts of less than 1 inch.
The split shaft allows the second shaft to spin at a slighlt lower speed and you can even change the speed by moving the power turbine blades on the take off power shaft a little farther or closer to the primary shaft.