49th U.S. Rock Mechanics/Geomechanics Symposium,
28 June-1 July,
San Francisco, California
2015. American Rock Mechanics Association
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This article proposes a methodology for building a rock mass model for the Toquepala Mine. This model will be used as an input for analyses to evaluate the stability of the current and future open pit slopes. The rock mass modeling process can be divided into two phases: a database building phase which involves gap analysis and data collection, compilation and validation; and an analysis phase that involves data assessment and the definition of rock mass units (RMUs). This article briefly describes each of these phases and how they have been applied at the Toquepala Mine, with emphasis on the data assessment and definition of the different RMUs.
Toquepala is a large open pit copper mine owned and operated by Southern Copper Corporation. It is located in Jorge Basadre Province in the south of Peru, about 160 km northeast of Tacna. The Toquepala Mine has been in operation since the late 1950s. In the 1980s, Call and Nicholas Inc. (CNI) developed an early slope design. Later, in 2000, updated slope design criteria were prepared by a joint collaboration of Golder Associates Ltd. (Golder), Itasca Consulting Group Inc. (Itasca) and Piteau Associates Engineering Ltd. (Piteau). As part of this later study, the rock mass characterization was updated.
The rock mass model developed for the 2000 slope design study was based on a series of mapping, drilling and laboratory testing campaigns. The laboratory testing program included a limited number of triaxial compressive strength tests. Following compilation of these data, rock mass units (RMUs) were defined based on lithology and the presence or absence of calcium sulfates (i.e., gypsum and anhydrite).
During the last 15 years, the Toquepala pit has grown. Pit slopes are currently on the order of 700 m high, and the next phase of mine development (Phase 5) will increase the slope height to approximately 950 m. Given this significant increase in slope height, and anticipated changes to the competency of the rock mass with increasing depth, it was considered prudent to update the rock mass model and slope design.
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