Whenever any assessment is levied on any property for further, separate or additional improvement under the provisions of this code or any law of this state, such assessment shall be a subsequent lien upon the property so assessed to the lien of the unpaid assessments theretofore made for the original improvement. Whenever any assessment is made for such further, separate or additional improvement on property on which an existing assessment has been levied for improvements, such further, separate or additional assessment for improvement shall not be construed or considered as for one and the same improvement, or for the same purpose or for the same benefit, or as a double assessment for improvements against the property being assessed for the payment of the cost and expense of such improvement but shall be considered and construed as a separate, distinct, single and independent improvement on and of benefit to the property so assessed. All assessments so levied or bonds or warrants issued payable from the same shall be considered and construed as assessments levied or bonds or warrants issued for separate, distinct, single and independent improvements and benefits on and to the property so assessed.