(a) The Presiding Judge or the Presiding Judge of the Criminal Division of the Fifteenth Judicial Circuit, upon motion of the district attorney for the circuit, shall empanel as many additional grand juries for the circuit to sit or be in session simultaneously or otherwise for such duration of time and for such purposes as may be necessary for the orderly and expeditious presentation of criminal cases therein.
(b) The empanelling of additional grand juries as provided herein shall not operate so as to discharge or dissolve any other grand jury which may be then or thereafter in session unless specifically ordered by the court on motion of the district attorney for the circuit.