Hi Vinod,
The actual RACH failure is only due to collision of RACHs since any subscriber can think of starting a call/sending sms at any time so probibility of collisions are high in RACH phase. But it would not be pegged in any stat at any vendor.
The RACH failure which is pegged at some vendors is the RACH failure detected after reception of a RACH.
This failure can be due to CRC check fail of this received RACH, UL level below set threshold. Distance exceeds TA limit.