Goathill North Rockpile Mitigation

The Goat Hill North Rock Pile Mitigation (GHN) project is a striking example of Skanska’s expertise with safe use of heavy equipment on challenging terrain. Chevron Mining’s Questa Mine, located in remote northern New Mexico, produces molybdenum, a metal used as an alloying element in steel making. An open pit mine was operated at Questa from the late 1950’s to the mid 1970’s. The GHN Rock Pile contains
non-ore rock from the open pit mine that was placed in the steep upper end of Goat Hill Gulch. Part of the non-ore rock was placed on an ancient
landslide, which caused a large portion of the rock pile to slowly creep down slope. Chevron Mining’s geotechnical investigation indicated that the creeping pile posed no immediate threat to life or infrastructure on or off the property. However, the need to safely stabilize the pile before performing any surface work in the area became clear.

Developing the project

A four-phase plan to reclaim the rock pile was prepared by Chevron Mining’s lead engineering consultant, Norwest Corporation, and was approved by the New Mexico state regulators.

Constructing the project

The work area was almost one half mile in length, with slopes ranging from 38° to 45°. With project safety of paramount concern, continuous monitoring was undertaken to measure displacement, groundwater conditions, and meteorological conditions. The plan’s Phase 1 entailed processing, haulage, and placement of 20,000 cubic yards of drain rock under what would become the toe of the stabilized pile. Phase 2 called for mass excavation of more than 500,000 cubic yards to form an initial buttress in the toe area of the existing rock pile. The cut materials
were moved down the face of the rock pile to build a stable buttress fill at slopes ranging from 2:1 to 2.5:1 (H:V). Phase 3 construction consisted of removing and redistributing the top of the rock pile by excavating about 800,000 cubic yards of it down to native ground. These cut materials were used to form stable slopes at 2:1 to 3:1 (H:V) for the remainder of the buttress fill. Phase 4 consisted of creating drainage controls to protect the re-graded surfaces. The project was located in the rugged Sangre de Cristo Mountains of New Mexico at an elevation of 10,000 feet.
Work was completed without a recordable safety or environmental incident.