Greg You

SLOPE STABILITY AND ROCKFALL HAZARD ANALYSIS IN OPEN PIT ZINC MINE

Rockfalls are a major safety hazard in open cut mines, particularly in large-scale deep pits. The geotechnical design relies on in-situ, site-specific, rock slope data to predict the trajectories and velocities of rockfalls that present a residual hazard in the mines. This paper presents slope stability analyses using both static general limit equilibrium methods and finite element stress analyses to estimate unstable areas and slope displacements in the mid-west slope at Glencore Zinc’s Handlebar Hill Open Cut mine at Mt. Isa, Queensland, Australia. A conventional program -RocFall- was used for the slope rockfall risk assessment. Results indicate the possible slope benches involved in the initiation of rockfalls, and the maximum run-out distance, which could be defined as the pits hazardous zone. A rockfall restraining system to absorb the impact energy of boulders and prevent them further falling was also modelled.

Finite Element Analysis of Rock Slope Stability Using Shear Strength Reduction Method

Finite element analysis incorporating the shear strength reduction method was applied to study the west slope stability of an open cut mine in Australia using Mohr–Coulomb and generalized Hoek–Brown criteria. The pit of the mine had multiphase excavations and reached 180 m in depth. The study investigated three slope configurations, namely, Stage 1 inter ramp slope 43°, Stage 2 inter ramp slope 49° and optimized Stage 2 slope 54°. When implementing the generalized Hoek–Brown failure criterion, the equivalent factor of safety was 1.96, 1.87 and 1.40 under dry slope for the three configurations, respectively. However, under partly saturated conditions, the optimised slope would have a factor of safety 1.16. Furthermore, the generalised Hoek–Brown criterion generated lower factors of safety than the Mohr–Coulomb failure criterion. The difference is related to an overestimation of the shear strength parameters by the linear Mohr–Coulomb criterion under low confining stresses compared with the non-linear Hoek–Brown.

Shallow Seismic Investigation of the Yangtze River Fault at Zhenjiang, Jiangsu Province, China

Debates on the Yangtze River Fault at Zhenjiang, Jiangsu Province, China have lasted for a long time. In order to clarify the stratigraphy, characteristics and activity of the fault, a large-scale shallow seismic investigation was conducted on the site. It involved 10 onsite field experiments, 5715 m long shallow seismic exploration and five geological drill holes, and consequent data processing and interpretation of the shallow seismic time profiles in combination with one geological profile and a satellite image. It was found that the loose Quaternary strata present good continuity in the area. Four pre-Cenozoic faults present in the bedrock (including the Yangtze River Fault), and two Quaternary faults cut the Quaternary sediments. Therefore, the existence of the Yangtze River Fault is verified, and its activity and characteristics are analyzed in this study.

Cracking Mechanism Along the North Batter of Maddingley Brown Coal Open Pit Mine, Victoria, Australia

Cracks manifested on the north batter at Maddingley Brown Coal Open Pit Mine, Victoria, Australia in November 2013. The crack opened varies from trace to approximately 150 mm wide was located at about 20 m back from the coal face and extended for approximately 50 m on the eastern side and terminated 10 m away from the access road. Site investigations and remedy measures were implemented immediately after the cracking. This study involves in a three dimensional modeling on the cracking mechanism using finite element method (FEM) encoded in Plaxis 3D software program. From the study, it was found that the initial model based on north batter being stable for many decades tended to lead a circular critical path while the model after overburden removal showed a trend of block sliding. The safety factor of initial north batter was 1.38 through safety analysis while it was decreased to 1.17 for the coal batter after overburden removal. But the simulated shear and tensile strains indicated that the coal batter after overburden removal in fact experienced block failure. Furthermore, the simulated location of cracking was in good agreement with the actual location, and the simulated heave of the coal seam was in good agreement with the experience in Victoria brown coal open pit mining. The observed vertical crack would be a combined action of the overburden removal and the groundwater flow in the unconfined aquifer.

Mining and the Environment

While sustainable development is often viewed as a task for national governments this paper asks what can be done on a regional level. The first part of the paper deals with the general principles of sustainable development according to the concept of the sustainability triangle are explained. It is shown that while economic sustainability prevails during the first stages of the development of a country at a later stage social and environmental sustainability become essential for the mid- and long-term development and stability of an economy. In the second part it is shown that sustainable development is not a task for central government alone but is also an important challenge for regional governments. Some tasks necessary for a sustainable development like e. g. groundwater protection can even be better executed on a regional level. Therefore, special emphasis will be put on water protection in this part of the paper. In spite of the responsibility to be taken by regional governments the existence of significant spillover effects between regions makes it necessary to coordinate the policy between central government and regional governments as well as between different regional governments in order achieve overall efficient results.

KINEMATIC ASSESSMENT OF SLOPES AT HANDLEBAR HILL OPEN CUT MINE, MT. ISA, QUEENSLAND, AUSTRALIA

A complete kinematic analysis was conducted for the west slope at the Handlebar Hill mine using the Rocscience/Dips 6.0 software. The west slope was divided into three zones: W1 (south-west), W2 (mid-west) and W3 (north-west), which were then subdivided into nine small elements to increase the certainty of parameters. This enabled the analysis to define the potential kinematics of motions of critical structures. Small scale joints, bedding, faults, shears along the discontinuities were plotted and the data were analysed systematically. The results indicated that the potential toppling mode created by discontinuities can lead to direct/flexural toppling failure. The kinematic feasibility also revealed that the intersections of the discontinuities within the critical zone can structurally control the wedge planar failure modes. The results will assist the mine geotechnical engineers to understand the potential slope failure mechanisms and their locations.