Geotechnical characterization of ore related to mudrushes in block caving mining

Abstract

Mudrushes are sudden inflows of mud ore into underground miningfacilities. They may cause harm to people and equipment, productiondelays, dilution of ore, and mine closure. The aim of this work is to charac-terize, by geotechnical laboratory tests, mud from a block cave and toderive mechanical reasons for the failure of this material while it is beingdrawn. We used ore samples from extraction points closed due to mudrushpotential from the Diablo Regimiento Sector at El Teniente Mine, whichrepresent the three types of mud ore. Characterization showed that thesamples comprise gravel and sand with silt and clay grain sizes, whereasthe fine particles are classified as low-plasticity silt and clay. Only smalldifferences in fines content, density, and packing were found. The effectsof density and degree of saturation on ore strength in unconfinedconditions were evaluated. It was found that relative density is the mostrelevant variable that governs the unconfined strength. Triaxial consol-idated tests showed a linear relationship between deviatoric strength andeffective confining stress. Deviatoric strength is related to the capacity toflow under triaxial conditions, and consequently it could be related tomudrushes. Unconsolidated, saturated material exhibited a very lowdeviatoric maximum strength followed by static liquefaction, resulting inresidual strength values close to zero. In terms of mining, the geotechnicaltests were related to the draw rate and the saturation conditions: a highrate of draw could cause unconsolidated conditions as the strength of themud decreases close to zero, while a low extraction rate could be related toconsolidated conditions where the ore is allowed to release the porepressure. If the ore is under unsaturated conditions it presents a lower riskas it will develop uniaxial strength.