PERFORMANCE OF ROADHEADERS AT HARLAN, KY, DIVERSION TUNNELS

Four side-by-side tunnels have recently been completed for the purpose of flood control for the town of Harlan, Kentucky. The inverted ''U'' shaped tunnels average 590 m (1935 ft) in length and are 9.75 m (32 ft) high by 10.4 m (34 ft) wide. They were constructed utilizing roadheaders through massive siltstone containing an average of 58 percent quartz and having an average unconfined compressive strength of 469 MPa (6800 psi). Two machines of different manufacture and size were used for the construction of the top heading and the performance of each has been documented A comparison to drill and blast is possible since the bottom heading was excavated in this manner.