Engineering Highway 60

Construction Progress Through Difficult Country Is Made Rapid and Simple by Modern Road - Building Machinery and Methods

By A. F. RATH, Resident Engineer

This DIVISION of U. S. 60 is now well in its fourth year of construction. Work was started in the late spring of 1931 at Globe, the county seat of Gila County, and to date 45 miles of it have been completed. It crosses the Crook National Forest, the San Carlos and Ft. Apache Indian Reservations, and will terminate at Showlow, a town situated in the Sitgreaves National Forest in Navajo County. When completed Highway 60 will provide an all-year-round route through the state, from California to New Mexico, without a serious snow hazard to confront the traveler, such as is now found in places along temporary U. S. 60.

The completed part was let in six different contracts. The first section, beginning at Globe, traversed an easy rolling country, but as the work advanced it was met with increasing difficulties, and by the time the Salt River Canyon, 38 miles from the beginning, was reached, the exceedingly rugged terrain had made road building a very disturbing task.

The whole route as it passes through a low, rolling country, slightly in excess of 3,000 feet above sea level, never reaching a height above 6,500 feet, offers many changes in scenery and vegetation. The boundary line between desert and mountain is distinguished by an abrupt change in plant life. Cactus, greasewood and mesquite give way to walnut, oak and pine and, in one small isolated section, cacti are content to thrive in the shadow of tall pines, as though nature became confused while attempting a division and ended with a compromise by permitting both to grow together.

The Salt River Canyon provides a multi-colored series of horizontal rock formations, not unlike the Grand Canyon, and offers many inspiring views. In addition to its grandeur it also provided both engineer and contractor with many surprising difficulties during the location and construction of this road, as it winds down one canyon wall and up the other side.

The present construction activity is confined to grading a 3.9 mile section that embraces most of the rougher country before the end of this division is reached. This section, better known as NRH-99G, of the Globe-Showlow Highway, was awarded to the George W. Orr Contracting Company last October, for the sum of $316,938.38. Of this amount 87 per cent is applicable to excavation, overbreakage and haul, while the balance, or 13 per cent, is applied to drainage structures and guard fence.

The geological formation is chiefly lime and sandstone, with the usual talus slopes commonly found here. These slopes cover rock ledges, faults and fissures, and make it almost impossible to determine the nature of cuts until they are drilled. The drilling is being done by both jackhammer and wellrig equipment. The wellrig provides a new type of drill for this work. It is a No. 26, Bucyrus-Armstrong, and bores an 8 inch hole. It is mounted on tracks, the kind in common use on tractors, carries its own power-plant and is a very mobile outfit and can reach its objective with a minimum of pioneer road building.

When drilling cuts, the formation permitting, the blast-holes are bored about five feet from the shoulder line and slightly below grade. This prevents a possible overbreakage and leaves no high places in the bottom of cuts. Should additional slope shots be required or ditches pulled the necessary drilling is done later with jackhammers. The lighter cuts are all drilled by jackhammer methods and two 310 foot Ingersoll-Rand compressors supply the air. So far these blast hole shots have (Continued on Page 25)