People sweeping the grave of Nabi SAW

Firstly understand why the authorities call for the sweeping around the blessed grave of Nabi Muhammad (S.A.W) repeatedly, many of those who convey Salaams upon Nabi (S.A.W) whilst they are near the grave, throw or insert pieces of paper from outside through the holes of the grating which land around the grave - side. These notes contain requests and strange demands. However, the graveside needs to be cleaned therefore sweeping is done. Moreover, for the upkeep of the cleanness of the graveside, if the grave yard is swept, then it is permissable.