The university grew at a rapid rate throughout the 1960s, with three colleges and many other buildings on campus being completed by the end of the decade. The 1970s saw further construction, but the university also encountered the biggest physical problem in its history. The university had been built above a tunnel on the disused Canterbury and Whitstable Railway. In July 1974 the tunnel collapsed, damaging part of the Cornwallis Building, which sank nearly a metre within about an hour on the evening of 11 July. Fortunately, the university had insurance against subsidence, so it was able to pay for the south-west corner of the building to be demolished and replaced by a new wing at the other end of the building. Building elsewhere included the Park Wood accommodation village and the Darwin houses in 1989.