Research Article Volume 2 Issue 5
1AMTC, University of Chile, Chile
2Mining Engineering Department, University of Chile, Chile
3Lundin Mining, Chile
Correspondence: Javier Vallejos, Electrical Engineering Department, Santiago, RM, Chile, Tel +562 9787 1000,
Received: August 04, 2018 | Published: December 31, 2018
Citation: Vallejos J, Miranda R, Azorin J, et al. Stability graph using major geological structures. Fluid Mech Res Int J. 2018;2(5):243-246. DOI: 10.15406/fmrij.2018.02.00044
Optimal stope dimension for underground mining using sublevel stopping method is decided ensuring excavation stability. This is done evaluating rock mass conditions during the whole mining period in order to reduce operational hazards thus ensuring continuous production. Mathew’s stability graph method is used as an analytical tool to achieve this purpose, but its original stability number has proven to be ineffective in the analysis of large scale slopes. Mathews B factor of joint orientation accounts for the influence minor discontinuities in the over break volume of slope’s walls. However, it does not reflect the scale difference between these discontinuities persistence and the slope’s size. Adverse oriented joint sets will imply low value B factor which will have a major effect on the stability number’s value while their actual influence on the slope’s wall over break may be immaterial. Major faults dimensions are comparable to large scale slope’s and thus their effect on these slopes over break volume is substantial compared to the one produced by the joints. This leads to the idea of calculating Mathew’s stability number using a B factor accounting for the effect of major faults in the stope wall’s over break.
Keywords: stability graph, sublevel stopping, mineroc, case study, stoping mines, rock mass behavior, compressive stress, re-calibrated, underground mine, rock mass, chilean sublevel, stoping mines, geotechnical, geological, potential excavation, exploited stopes
Instability of the surrounding rock to underground mine openings is an ever-present threat to the safety of both people and equipment, this being this critical for sublevel stoping mines to ensure continuous production. Several tools, has been created to predict the rock mass behaviour, one of them is the empirical stability graph method developed by Mathews1 based on the shape factor, S, and the stability number, N. The shape factor is related to the geometry of the wall. Whereas, the stability number represents the characteristics of the rock mass.
S=AreawallPerimeterwall,N=Q`·A·B·C
The following years different authors expanded the original database, re-calibrated the stability number factors and proposed new stability boundaries.3‒7 The most comprehensive one was developed by Mawdesley.8 It contains more than 400 open stoping case studies from over 38 mines in North America, Australia, and England (Figure 2). Despite the significant amount of data collected, Chilean open stoping case studies were not considered. Therefore, particular geotechnical conditions and operational standards for Chilean sublevel stoping mines, are not being truly represented in the literature stability graphs. The objective is to develop geotechnical guidelines for mine design that reflect the geotechnical/geological and mining conditions of an underground mining complex. This paper presents the results of an empirical stability study of exploited slopes in different sectors of an underground mining complex located in Atacama Region, Chile, using Mineroc to perform the back analysis of the stopes performance.
Vol.Dilution=Overbreak of volume wallwall
ELOS=Overbreak of volume wallAreawall
Different sectors from the mining complex were analysed in order to develop local stability curves. Information was compiled using Mineroc software, obtaining over-break volume, area and hydraulic radio per wall. These values are then used to calculate volumetric dilution of exploited stopes. The Stability Number N was obtained by analysing different geotechnical and geological parameters RQD,13 Joint set Number (Jr), Joint roughness number (Jr), Joint alteration number (Ja), UCS were assigned by the Geotechnical Unit of the slope’s surrounding rock. The A factor was calculated analysing the induced stresses obtained from the Stewart & Forsyth graphical method and the UCS,14 B factor was calculated using the angle between the orientation of major geological structure and the walls of the stope and the Gravity factor C is obtained analyzing the Dip angle of each wall (Figure 5).
The database consisting of 709 walls (different CMS measurements were taken throughout the mining period of the stopes). The following figure presents the database and ELOS curves proposed for the mining complex (maximizing the PSS of the Curves11 This graph presents 3 stability curves describing areas characterized by ELOS 0.5m, 2m and 4m per wall (Figure 6). Evaluation of a new design using local stability curve. In order to evaluate a new potential excavation, Mineroc Software is equipped with a slope design module, this module estimates the stability number N (calculating Q', A, B and C factors) using the stored information from the mine and calculates the hydraulic radius for each of the walls based on the desired dimensions. The points (RH, N) are plotted on the graph identifying in which stability zone it shall be located. This process is done automatically to analyze the response of the design to variations of the geotechnical parameters and the stope geometry. The following example will explain the utility of local stability curves and how to obtain an estimated ELOS per wall (Table 1) (Figure 7). To obtain the stability number N, the site of the excavation is characterized by the following values, developing an overburden stress model in the site.15,16 As it is shown in (Table 2) (Figure 8) (Figure 9) the side walls are very close to ELOS 0.5m curve, the end walls are located above ELOS 2m curve and whereas the back of the store is located below ELOS 4m curve, being necessary to control the extraction.17‒21
Geotechnical |
Information stress |
UCS50 [Mpa] |
253 |
RQD |
65 |
Jn |
12 |
Jr |
1.5 |
Ja |
1.5 |
Table 1 Geological faults
Wall |
ELOS |
Back |
4 m |
Hanging Wall (HW) |
0.5 m |
Foot Wall(FW) |
0.5 m |
End Wall 1 |
2 m |
End Wall 2 |
2 m |
Table 2 Geological faults
Dimention |
|
Long [m] |
40 |
Width[m] |
25 |
High [m] |
33 |
Dip [º] |
90 |
Strike [º] |
65 |
Depth[m] |
270 |
Figure 7 Stope design
Among the main benefits of using the new local stability graph based on wall ELOS:
It is possible to obtain an estimation of the dilution of new designs based on curves proposed specifically for mining operations. As a result of the study, a standardized database with geotechnical / geological / mining information has been developed in order to analyze new designs. It is possible to identify similar conditions in terms of the rock mass quality (N) and dimensions (RH) of the new slope designs analysing how they would perform under similar conditions. The new guidelines allow the design of optimized stopes in terms of the expected ELOS using major geological structures compared to the original stability curves which are subjective. To control over-break and dilution in sublevel sloping methods, it is necessary to adapt the tools proposed in the literature to the local conditions of the mine. Mineroc software allows the automation and standardization of stability analysis (Table 3)(Table 4).
𝜎𝑍𝑍 |
0.038 *Depth [m] |
𝜎𝑁𝑆 |
0.053*Depth [m |
𝜎𝐸𝑊 |
0.053*Depth [m] |
Table 3 Geological faults
Dip [º] |
82 |
DipDir[º] |
265 |
Dip [º] |
71 |
DipDir[º] |
248 |
Table 4 Geological faults
New guidelines for mining design have been proposed based on a dilution criterion per wall:
None.
The author declares that there are no conflicts of interest.
©2018 Vallejos, et al. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially.