Abstract

CASTRO, R.L.; BASAURE, K.; PALMA, S.  and  VALLEJOS, J.. Geotechnical characterization of ore related to mudrushes in block caving mining. J. S. Afr. Inst. Min. Metall. [online]. 2017, vol.117, n.3, pp.275-284. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2017/v117n3a9.

Mudrushes are sudden inflows of mud ore into underground mining facilities. They may cause harm to people and equipment, production delays, dilution of ore, and mine closure. The aim of this work is to characterize, by geotechnical laboratory tests, mud from a block cave and to derive mechanical reasons for the failure of this material while it is being drawn. We used ore samples from extraction points closed due to mudrush potential from the Diablo Regimiento Sector at El Teniente Mine, which represent the three types of mud ore. Characterization showed that the samples comprise gravel and sand with silt and clay grain sizes, whereas the fine particles are classified as low-plasticity silt and clay. Only small differences in fines content, density, and packing were found. The effects of density and degree of saturation on ore strength in unconfined conditions were evaluated. It was found that relative density is the most relevant variable that governs the unconfined strength. Triaxial consolidated tests showed a linear relationship between deviatoric strength and effective confining stress. Deviatoric strength is related to the capacity to flow under triaxial conditions, and consequently it could be related to mudrushes. Unconsolidated, saturated material exhibited a very low deviatoric maximum strength followed by static liquefaction, resulting in residual strength values close to zero. In terms of mining, the geotechnical tests were related to the draw rate and the saturation conditions: a high rate of draw could cause unconsolidated conditions as the strength of the mud decreases close to zero, while a low extraction rate could be related to consolidated conditions where the ore is allowed to release the pore pressure. If the ore is under unsaturated conditions it presents a lower risk as it will develop uniaxial strength.

Keywords : mudrush; block caving; geotechnical characterization.

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