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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
You give no detail of the type and size of cable you want to put onto this tray. Cable manufacturers will give you the minimum bending radi for cables. Usually on a large armoured cable it is about 8 times the overall cable diameter.
It is good practice and often obligatory to ensure some services are seperated - 11kV cable from a data cable.
Consider the loading on the tray - how many deep th cables are going to be laid.
You should now have the makings of working out your minimum radius.
There are other things to take into account - load, deflection, grouping, EMC etc.