Numerical analysis and geophysical monitoring for stability assessment of the Northwest tailings dam at Westwood Mine

The Westwood Mine aims to reuse the tailings storage facility #1(TSF #1) for solid waste storage, but,downstream of the Northwest dike is considered critical in terms of stability. This paper uses numerical modeling along with geophysical monitoring for assessing the Northwest dike stability during the restoration phase. The impact of waste rock deposition in the upstream TSF #1 is considered. The geophysical monitoring is based on electrical resistivity methods and was used to investigate the internal structure of the dike embankment in different deposition stages. The numerical simulations were performed with SLOPE/W code. The results show a factor of safety well above the minimum recommended value of 1.5. Geophysical monitoring revealed a vertical variation in the electrical resistivity across the dike, which indicates a multilayer structure of the embankment. Without any current in situ data, the geophysical monitoring helped estimating the nature of the materials used and the internal structure of the embankment. These interpretations were validated by geological observation of geotechnical log of the embankment. Based on this study, it is recommended that the water polishing pond be partly filled before waste rock is deposited in TSF #1. In addition, to ensure the stability of the dike, the piezometric head monitoring prior to and during waste rock deposition is recommended.

Earthquake dynamic response behavior of Xiangchong valley type tailings impoundment in Yunnan, China

Tailings impoundments can potentially collapse due to damage caused by earthquakes,which has frequently occurred around the world.This study takes the proposed valley type tailings impoundment in Yunnan as the research object to analyze the dynamic response behavior under earthquake action with both numerical simulation and physical model test(1:300).The results of both tests show that the dynamic response of the valley type tailings impoundment is characterized by"medium stiffness effect",in other words,in a certain range,the"softer"the unsaturated tailings sand is,the more energy it can dissipate,which leads the decrease of the value of the acceleration amplification factor.In addition,the peak acceleration of the monitoring points increases with the vertical elevation,which indicates that the"elevation amplification effect"exists in the tailings impoundment dynamic response.The middle part of the outer side of the raised embankment reacts more sensitive than the crest,which is similar to the slope dynamic response.The starter dam reacts sensitively under the earthquake excitation,which should be given more attention during the seismic design.The dynamic response rules reflected by the numerical simulation are consistent with the results monitored on the physical model test,although there are some differences between their values.The dynamic response rules of the valley type tailings impoundment can provide basis for the design of the similar projects in this region.

Current situation and forecast of environmental risks of a typical lead-zinc sulfide tailings impoundment based on its geochemical characteristics

The potential environmental implications of a Pb(Lead)-Zn(Zinc)sulfide tailing impoundment were found to be dependent on its geochemical characteristics.One typical lead-zinc sulfide tailing impoundment was studied.Ten boreholes were set with the grid method and 36 tailings were sampled and tested.According to the results of metal content analysis,the tailing samples contained considerably high contents of heavy metals,ranging from 6.99 to 89.0 mg/kg for Cd,75.3 to 602 mg/kg for Cu,0.53%to 2.63%for Pb and 0.30%to 2.54%for Zn.Most of the heavy metals in the sample matrix showed a uniform concentration distribution,except Cd.Cd,Pb,Zn,and Mn were associated with each other,and were considered to be the dominant contributors based on hierarchical cluster analysis.XRD,SEM and XPS were employed for evaluation of the tailing weathering characteristics,confirming that the tailings had undergone intensive weathering.The maximum potential acidity of the tailings reached 244 kg H2SO4/ton;furthermore,the bioavailability of heavy metals like Pb,Cd,Cr,Cu,and Zn was 37.8%,12.9%,12.2%,5.95%,and 5.46%respectively.These metals would be potentially released into drainage by the weathering process.Analysis of a gastrointestinal model showed that Pb,Cr,Ni and Cu contained in the tailings were high-risk metals.Thus,control of the heavy metals’migration and their environmental risks should be planned from the perspective of geochemistry.