The Three-Dimensional (3D) Numerical Stability Analysis of Hyttemalmen Open-Pit

Abstract

The purpose of this paper was to perform the 3D numerical calculations allowing slope stability analysis of Hyttemalmen open pit (location Kirkenes , Finnmark Province, Norway). After a ramp rock slide, which took place in December 2010, as well as some other small-scale rock slope stability problems, it proved necessary to perform a serious stability analyses. The Hyttemalmen open pit was designed with a depth up to 100 m, a bench height of 24 m and a ramp width of 10 m. The rock formation in the iron mining district of Kirkenes is called the Bjornevaten Group. This is the most structurally complicated area connected with tectonic process such as folding, faults and metamorphosis. The Bjornevaten Group is a volcano-sedimentary sequence. Rock slope stability depends on the mechanical properties of the rock, hydro-geological conditions, slope topography, joint set systems and seismic activity. However, rock slope stability is mainly connected with joint sets. Joints, or general discontinuities, are regarded as weak planes within rock which have strength reducing consequences with regard to rock strength. Discontinuities within the rock mass lead to very low tensile strength. Several simulations were performed utilising the RocLab (2007) software to estimate the gneiss cohesion for slopes of different height. The RocLab code is dedicated to estimate rock mass strength using the Hoek-Brown failure criterion. Utilising both the GSI index and the Hoek-Brown strength criterion the equivalent Mohr-Coulomb parameters (cohesion and angle of internal friction) can be calculated. The results of 3D numerical calculations (with FLA3D code) show that it is necessary to redesign the slope-bench system in the Hyttemalmen open pit. Changing slope inclination for lower stages is recommended. The minimum factor of safety should be equal 1.3. At the final planned stage of excavation, the factor of safety drops to 1.06 with failure surface ranging through all of the slopes. In the case of a slope angle 70° for lower stages, FS = 1.26, which is not enough to provide slope stability. Another series of calculations were therefore performed taking water table lowering into consideration, which increases the global safety factor. It was finally evaluated, that for a water table level of 72 m the factor of safety equals 1.3, which is enough to assure global open-pit stability.

3D and 2D Stability Analysis of Bentonite Slurry Trench with Shear Strength Reduction Technique and Limit Equilibrium Methods

“…The SSR technique, introduced by Zienkiewicz et al (1975), entails progressively reducing the soil strength parameters until failure occurs. Many researchers have effectively applied this technique in slope stability analysis [22][23][24]. Furthermore, the stability analysis of underground openings with complex geology and geometry [25,26] and large-scale open pit structures [27][28][29][30] has also been effectively carried out using the SSR technique.…”

“…Many researchers have effectively applied this technique in slope stability analysis [22][23][24]. Furthermore, the stability analysis of underground openings with complex geology and geometry [25,26] and large-scale open pit structures [27][28][29][30] has also been effectively carried out using the SSR technique. Here SSR technique was applied utilising tools such as RS2 [31], RS3 [32], FLAC2D [33], and FLAC3D [34] codes to evaluate the stability of excavation trenches with temporary support of bentonite slurry (γs = 10.5 ÷ 12.0 kN/m 3 ).…”

Application of Clay–rubber Mixtures for the Transportation Geotechnics—the Numerical Analysis

“…Numerical analyses were performed by the finite element method using the Z_Soil 2020 program [7]. In the case of the stability analysis, a simplification was used in the form of assuming a plane strain state, which is characteristic for linear objects [5,41,44]. When analyzing the VSS plate test, the assumption of axial symmetry was adopted, which is also correct for a homogeneous substrate (at least to the depth of the test range, which is defined as 2 D, where D is the diameter of the steel rigid plate used in the test.…”

Mine Slope Stability Based on Fusion Technology of InSAR Monitoring and Numerical Simulation

“…In order to ensure that open pit mining can be carried out safely and smoothly, the prediction and analysis of the stability of the open slope of the mining site is becoming more and more important. With the rapid development of computer science, numerical simulation analysis has become the main tool to study these kinds of engineering problems [5][6][7][8][9][10][11]. Software that fuses strength theory and numerical simulation can quickly and effectively simulate changes in slope stresses.…”