Estudio de las condiciones geotécnicas de cimentación de la estructura de la planta metalúrgica y estudio del depósito de relaves concesión de beneficio Planta Concentradora Campana

Abstract

The project is located on the Bella Union district, province of Caravelí, Arequipa Department, 15 kilometers away from the Bella Union town. The aim of this work is to develop a geological and geotechnical study in order to build treatment plant for metals ores and its tailings dam. Field work was to make project area recognition, geological mapping, geotechnical researchs with pits, diamond drilling, field trials, hydrothermal altered sampling and another test. Regionally geomorphology shows five units: plains, dejection cones, abandoned channels, slopes and hills. Stratigraphy shows lithologic units sedimentary with ages ranging from Paleozoic to recent Quaternary and igneous, and metamorphic country rocks. Structural Geology shows a tectonic development in a long time, the most important being the Andean massif folding, faulting and tectonic recent. Locally, recent sediments have been identified as alluvial, colluvial and fluvio- alluvional moreover intrusive rocks of the batholith of the coast and Bella Union andesites. Local structural geology only shows minor fractures. External Geodynamics shows erosion gullies and abandoned fluvio-alluvional streams to the south of the dam. Geotechnical exploration were performed with 18 pits and 8 diamond drillings, hydrothermal altered country rocks were sampled and field and lab test were performed. In the geotechnical conditions study of foundation soils the evaluation of the central section, the left abutment right abutment and the metallurgical plant area were made, suggesting for this case the improvement of the foundation with cement grout injections to fill bedrock fractures. Seismic hazard analysis was made using a probabilistic approach implemented in the CRISIS2007 computer program. The historic seismicity indicates that in the Bella Union district, have occurred intensities up to IX degrees on the Modified Mercalli scale. Static and pseudoestatic stability analysis has been performed, the results indicate that the dam is stable under static and seismic conditions. The design of the dam was based on a starter dam which will be raised gradually in various stages of growth, following the method of construction downstream. Geotechnical conditions evaluation of foundation soils indicate that: -In the central section of the dam: according to the characteristics of silty sand, is described as loose to moderately loose up to 4.5 m, underlay silty gravel with better support conditions. In the concentrator plant, rock in sector East is described as low feature geomechanical, in the West presents coverage of 5.5 m of sandy gravel with silt and silty sand, underlay weathered and fractured volcanic rock. For the construction of the central section of the dam, should be remove and dispose of, in the sector of the stream channel, the 4.5 m unsuitable material, dig on sidewalks to the stirrups progressively reducing its depth; you will also need to compact cutoff level, verifying that the building is in silty gravel. It is recommended, for tailings dam stirrups, eliminate the superficial coverage of 2.0 m and it will also be necessary a densification treatment by compaction below 2 m. For the concentrator plant area, it is recommended to remove 4 m of weathered and fractured rock in east sector. The improvement of the foundation with cement grout injections is necessary to fill fractures in the bedrock.