If BankNifty breaks the trendline with a strong selling volume, then you may witness 30500 levels. However, it may touch 31150 if it gives a breakout above 30930. Moreover, I also found that there is a bearish divergence in 5 and 15-minute charts which may be valid for the first 30 minutes of trading.
Being an expiry day, Open Interest also suggests that expiry might be in the range of 30500 - 30100. So, I believe that 30500 will act as a support and 30100 will be a strong resistance level.