Abstract
This article introduces a hassle-free methodology for geotechnical parameters to be obtained from correlations between geophysics and CPT field tests in tailings dams undergoing the decommissioning process, which are reasonably representative of site conditions, from the very early project stages, with extensive coverage of all impoundment parts, without the requirement for large-size drilling programs. The development methodology consists of running direct (CPT) and indirect (geophysics) tests within the same area of the tailings dam to be decommissioned, with information crosschecking, thus allowing for results to be presented as adjustment equations, capable of describing tailings undrained shear strength based on geophysical survey data. A dam within the region known as Iron Quadrangle, in the state of Minas Gerais, Brazil, was selected to pilot the tests. The results obtained showed consistent adjustments, thus validating the proposed methodology as a complementary geotechnical investigation tool, and also enabling an optimized investigation plan to be proposed for similar tailings dams undergoing a mining process, so as to provide better assessment of the safety conditions of the proposals for deactivation with reduced schedule and resource savings.
Highlights
Obtaining geotechnical parameters to develop stability analyses in tailings dams undergoing a deactivation process has evolved towards the deployment of site tests with direct strength measurement, whereby the Cone Penetration Test (CPT) stands out due to the array of existing correlations between cone penetration strength and undrained shear strength of saturated tailings, with references in literature including recent articles published by Olson and Stark (2003), Robertson (2010), and Jefferies and Been (2015)
The CPT performance methodology is simple and quick, and the interpretation of results is directly obtained by its own driving equipment software, when we talk about tailings dam deactivation projects, it is almost impossible to use driving spots to cover the whole impoundment area, either due to high costs associated with the large number of tests, or due to the impracticability of moving equipment over the impoundment that most of the times is partially filled with water or lowconsistency slime and as such does not allow for equipment traffic and support
The proposed methodology includes using the averages obtained from two lengthwise sections (TRVGA_20 and TRVGA_22) for Electrical Resistivity geophysics (Ohm x m) and undrained shear strength (KPa) based on CPTu tests, with linear interpolation of average results according to the reservoir depth, as per the sequence under items 2.1 and 2.2
Summary
Obtaining geotechnical parameters to develop stability analyses in tailings dams undergoing a deactivation process has evolved towards the deployment of site tests with direct strength measurement, whereby the Cone Penetration Test (CPT) stands out due to the array of existing correlations between cone penetration strength and undrained shear strength of saturated tailings, with references in literature including recent articles published by Olson and Stark (2003), Robertson (2010), and Jefferies and Been (2015). the CPT performance methodology is simple and quick, and the interpretation of results is directly obtained by its own driving equipment software, when we talk about tailings dam deactivation projects, it is almost impossible to use driving spots to cover the whole impoundment area, either due to high costs associated with the large number of tests, or due to the impracticability of moving equipment over the impoundment that most of the times is partially filled with water or lowconsistency slime and as such does not allow for equipment traffic and support. The risk of bogging due to the weight of the equipment in areas off the tailings beach restrict investigations to areas where driving equipment may safely operate, information collection being usually restricted to tailings beaches. Information collected from such locations is randomly extrapolated to the remaining portions of the dam, which brings about great uncertainty whenever the necessary actions for deactivation and stability analysis are carried out
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