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Geological Approach to Rock Mass Stability and Feasibility During the Exploitation and Excavation in Hard Rock Masses (CROSBI ID 567707)

Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija

Tomašić, Ivan ; Kršinić, Ana Geological Approach to Rock Mass Stability and Feasibility During the Exploitation and Excavation in Hard Rock Masses // 4. Hrvatski geološki kongres s međunarodnim sudjelovanjem - Knjiga sažetaka / Horvat, Marija (ur.). Zagreb: Hrvatski geološki institut, 2010. str. 178-179

Podaci o odgovornosti

Tomašić, Ivan ; Kršinić, Ana

engleski

Geological Approach to Rock Mass Stability and Feasibility During the Exploitation and Excavation in Hard Rock Masses

This paper describes geological approach, including field structural geology studies and geological methods important for rock slope design, stability and sustainable exploitation and excavation of crude rock masses. In view of the importance of rock slope stability for economics and safety of opencast mining, there are other remarkable possibilities for mining engineers to obtain a reliable estimation for safe and sustainable excavation. Blasting, fragmentation, crumbling, exploitation of natural stone blocks and projecting of height and width of benches or a rock slope design are some of them. In this paper, among all other, determination of stable excavation fronts is by discontinuity analysis emphasized. The results of analyses must be the most stable rock mass and the most favorable orientation of exploitation fronts in relation to discontinuity inclination and orientations. Stable rock mass is very important for safety and economics of exploitation and fragmentation in quarries, in other open pit mines, in civil engineering works and during formation of cuttings and embankments as well. Stable rock mass and discontinuities (bedding plains and joints) have great influence on blasting works and on determination of other exploitation factors. Influence of geological features through adjustment of blasting parameters must be taken into consideration. During blasting rock mass breaks into small pieces favorable for crumbling in machinery. The size of stone pieces depends on using of rock mass as aggregates or as much greater stone pieces for armourstone. Detailed optimal determination of discontinuities, discontinuity density and discontinuity spatial relations is also important for evaluation and utilization of large stone blocks during the exploitation of natural stone blocks. The analysis has been based on graphical method by HOEK & BRAY (1974) and on research and experience by TOMAŠIĆ (1986 and 1989) and TOMAŠIĆ & JAKIĆ (1990). On the base of exploration, perception of rock structure, discontinuity measuring and analyses in many examples of hard rock masses, mostly in quarries, important conclusion has been established and carried out. There are three borderline examples (fig. 1a, b, c) of relations between exploitation front orientation and orientation of discontinuities (TOMAŠIĆ, 1989). First example (fig. 1a) is the case, when strike of exploitation front is parallel with strike of discontinuities (mostly bedding plains and rarely joints). Excavation slope has inclination of 70° in direction of working platform, but discontinuities possible for inducing of sliding, have dip between 35° (friction angle φ) and 70°. In this case ideal geometrical conditions exist for producing controlled or uncontrolled sliding. All previously mentioned also depend about influence of geotechnical characteristics of rock mass and discontinuity roughness on contact surfaces. Influence of water pressure is also important for sliding and shear strength. In second example, (fig. 1b), the strike of excavation front is parallel with strike of discontinuities (mostly bedding plains and rarely joints). But in this case the difference is emphasized with dip of discontinuities in direction of rock mass or in direction of exploitation. Stability of rock mass in this example is more favorable than in the first example. Third example is the case when strike of excavation slope (dip is 70°) and strike of discontinuities (mostly bedding plains and rarely joints) are mutually perpendicular (fig. 1c). The results, based on discontinuity analysis and on field experience, have confirmed that third example (fig. 1c) is the most favorable for rock stability. Favorableness discrepancies range from that position to bring out ±20°. The rock slope could be stable at dip angle more than 70°. In that case HOEK & BRAY (1974) emphasized that those unfavorable intersections between discontinuities do not exist or exist much less inside the surface between friction angle (35º in this example) and angle of rock slope inclination (70º). This position of rock slope regarding discontinuities could be the most favorable for rock mass stability. Based on our experience during the exploration we determined that successfulness of blasting directly depends on rock mass stability. On the geotechnical basis stable rock mass intensify controlling of rock fragmentation. Why is that possible? Stable rock mass enables optimal resistance to explosive charges and maximal utilization of its energy during the fragmentation. In that case primary blasting works achieves optimal fragmentation in stable rock mass and the planed desired effect. Unstable rock mass does not enable high quality of blasting and optimal fragmentation because of low resistance of unstable rock mass to explosive charge during the explosion. In spite of high adjusted blasting parameters, energy of explosion spends on pushing rock mass down the slope in direction of working platform and fragmentation is not complete. Consequently, high percent of over break excavation stone blocks require much expensive costs using a secondary blasting. According before stated better fragmentation is possible in example of orientation of excavation fronts in relation on discontinuities on fig. 1b than in the case of on fig. 1a. During the blasting the most favorable intersection of discontinues with excavation slope range from 45° to 90°. But this reality is not proved in wholeness during the field research. Maybe the most resistance of rock mass to blasting is when discontinuities tend to be perpendicular to the excavation front. It is favorable for fragmentation of rock mass. Utilization of stone blocks from natural stone deposits is favorable when discontinuities are parallel or perpendicular in relation to the exploitation front. Also utilization depends on the discontinuity spacing (discontinuity density). Reorientation of exploitation slopes in position of stable rock mass enable optimal using of blasting methods during the excavation and fragmentation of rock mass. Optimal fragmentation of rock mass enables low expenses of blasting and favorable economic conditions for exploitation. This paper demonstrates that used method has an important application during the exploitation and excavation of hard rock masses.

Rock Mass Stability; Excavation front; Discontinuities; Blasting works

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Podaci o prilogu

178-179.

2010.

objavljeno

Podaci o matičnoj publikaciji

4. Hrvatski geološki kongres s međunarodnim sudjelovanjem - Knjiga sažetaka

Horvat, Marija

Zagreb: Hrvatski geološki institut

978-953-6907-23-6

Podaci o skupu

4. Hrvatski geološki kongres s međunarodnim sudjelovanjem

poster

14.10.2010-15.10.2010

Šibenik, Hrvatska

Povezanost rada

Rudarstvo, nafta i geološko inženjerstvo