State and federal experts were examining the site of a massive sinkhole on Thursday, trying to determine what caused it and how it can be repaired. The collapse happened along State Highway 516 just west of Dover. It took the westbound lane of the two-lane highway with it into a lake from which a family owned asphalt company has been dredging sand and gravel for years. Some estimate the size of the gaping hole as big as several football fields wide. The site attracted dozens of spectators on Thursday who could hardly describe what they were seeing.