NSW govt under fire on train wall collapse THE NSW government must explain why it failed to act on safety warnings before a retaining wall at a western Sydney train station collapsed, the opposition says. The wall at Harris Park station collapsed onto the platform and tracks earlier this week following several days of heavy rain. RailCorp engineers, however, had been alerted to the problems with the wall six months ago, News Ltd reports. Opposition transport spokeswoman Penny Sharpe has called on transport minister Gladys Berejiklian to explain what RailCorp knew about the wall's problems. "The Harris Park land slip was extremely serious - it was a miracle nobody was injured when soil fell onto the tracks," Ms Sharpe said. We now know that Parramatta Council identified problems at Harris Park as far back as December - and alerted the O'Farrell government. Ms Berejiklian said Sydney Trains was investigating the collapse. "I'm advised a geotechnical investigation of the retaining wall occurred in December 2012," Ms Berejiklian said. No issues were identified and preliminary findings suggest Sunday's incident was caused by a build-up of water behind the fall following the recent rain. She said rail infrastructure spending was up 14 per cent this financial year.