It is a necessity for mine fillings to achieve greater resistance while also being a means of support to maintain good rock stability, especially in underground areas that are increasingly deeper and with large open cavities. The properties of the fill are, therefore, of particular interest. Cemented rock fill (CRF) is a good alternative solution for the sublevel stoping (SLS) mining method, where higher fill volumes and efficient resistance values are required to support the walls of the mined stope, providing greater mineral recovery in the different lateral sublevels.

Cemented Rock Fill (CRF) Application

Cemented rock fill is a mixture of sterile crushed and/or classified waste rock from mine development, plus proportions of cement and water. Cement, as a binder of the mixture, increases resistance to compression stresses. Success factors include the physical properties of the filling material, the granulometry of the sterile material, and the mix design of the filling.

Mix designs can be optimized taking into account the following: (i) calculation of the minimum resistance required to ensure the stability of the backfill; (ii) optimization of the mix variables to produce minimum resistance values with the least use of cement; (iii) implementation of quality control procedures and performance monitoring of the stope filling procedure. This methodology ensures the safety and quality of the process, as well as a reduction in operating costs.

The resistance required for the use of backfills depends on the exploitation method, the geology of the mineralized body, the drilling design, and possible failure modes. Mitchell & Roettger (1989) described the four possible failure modes of cemented rock fill in a mine: (i) Sliding: occurs due to low resistance to friction between the backfill and the rock wall; (ii) Crushing: occurs when the induced stress exceeds the uniaxial compressive strength of a filling mass; (iii) Flexural: occurs when a filling mass has a low tensile strength; (iv) Caving: may be the result of an arc and rotational failure due to low shear strength in a rock wall.

Case study: Cemented rock fill optimization

INCIMMET has been operating a modular concrete plant for the production of cemented paste at Buenaventura’s Tambomayo Mining Unit. The exploitation method is Bench and Fill (B&F) in longitudinal and transverse mining; variants of the SLS method. To fill the open cavities, two types of backfill are used; rock fill and cemented rock fill, which, in addition to better controlling the structural support of the rock mass, allows for a greater recovery of the ore.

At first, a particles size of less than 3 inches was used. With this material at 95% and 5% cement, it has been possible to reach strengths of 0.4 MPa and 0.5 MPa at 7 days and 1.2 MPa at 28 days of curing. To improve the resistance at different time horizon, several tests and designs related to granulometry were carried out, improving the classification of the aggregate of the material less than 4 inches, but greater than 2 inches. With these corrected designs it was possible to obtain resistance of 0.8 MPa and 0.9 MPa at 7 days, and 1.8 MPa at 28 days.

Case study: Feasibility test of an underground mobile cemented rock fill mine plant

A mobile plant was installed in the Cerro Lindo Mining Unit of Nexa Resources Peru, with equipment including a cemented paste pumping system connected to a mix preparation chamber. Regarding mining infrastructure, there was a 25-meter-long chamber for the preparation of the mix and two other 12-meter chambers for the accumulation of waste and preparation of the mix, all located about 200 meters from the stopes.

In conclusion, cemented rock fill (CRF) has a high performance that gives immediate response to the excavation and reorients the efforts generated in a timely manner, guaranteeing the stability of the mine.

About INCIMMET

INCIMMET is mining contractor with 28 years of experience in the sector, providing integral solutions in excavation. Mine backfilling is one of the most recognized services in the company’s portfolio. We provide a EPCM approach: (i) characterization studies of materials available for backfill, (ii) selection of the most appropriate type of backfill according to the exploitation method, (iii) optimization and improvements of the existing mine backfill process, and (iv) procurement, construction, operation of plants, backfill transport and stopes filling. For futher information, contact: comercial@incimmet.com

Eduardo Cossio Chirinos – CEO Eduardo holds an MBA degree from IESE Business School, a bachelor’s degree in finance and a bachelor´s degree in management from Universidad Peruana de Ciencias Aplicadas (UPC). He also holds a specialization in commercial strategies from The University of Chicago (Chicago Booth) and a specialization in family businesses and corporate governance from IMD in Switzerland. Before taking the CEO position, Eduardo was INCIMMET´s Managing Director with commercial, financial and strategy responsibilities. Eduardo joined INCIMMET in 2010 as its CFO.

Image courtesy of INCIMMET