Thanks Michael, yes your file works fine, as for me not managed to do it by trimming, it is exactly what you say, many surfaces overlap each other so i hardly see/understand which part i'm trimming in that mess, i've tried by hiding all but one and then trim one by one by one but i can't say i got great result 'coz even after i trimmed all with outside circle and deleted outside excess areas i still have many overlapping surfaces with corners bending upwards so i've not known how to weld/merge them into that single flat nice surface you got (my screen-grab showing how surfaces are bending upwards=.

Luckily Marcos's solution worked so i managed to fix it with that technique.