The application of the face-perpendicular preconditioning technique for de-stressing seismically active geological structures

Abstract

A trial on de-stressing a dyke that was located 60 m ahead of mining faces was conducted through drilling face-perpendicular preconditioning holes that intersected and passed the dyke by two metres. A sticky explosive (Ug101s) with a density of 1.1 g/cc, charging amass of 30.4 kg, powder factor of 1.3 kg/tonne, with gassing gap and 5 m long tamping material were used. After detonating the holes, a small seismic magnitude was noted. As mining progressed towards the dyke and passing through the dyke, good ground conditions were observed. Numerical modelling was conducted to simulate rate of energy release (RER), major principal stress ahead of the mining faces and simulation of the ride. The results of the study showed a gradual decrease of sigma 1,RER and high possibility of large seismic events to occur when mining through the dyke and also increase in the ride at the vicinity of the dyke.

Keywords

Face-perpendicular preconditioning de-stressing RER hangingwall fracturing microseismicity numerical modelling dyke ride

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References

Adams

, Geyser

1999. Preconditioning of 43 Hangingwall Haulage at Kloof No. 4 Shaft. SARES 99 (ed. Hagan, T.O) SAIMM.

Brummer

RK.

1988. Active methods to combat the rockburst hazard in South African gold mines. Conference on Applied Rock Engineering, (CARE), IMM, Newcastle-upon-Tyne, London. p. 35–43.

Lightfoot

, Kullmann

, Toper

, Stewart

, Grodner

, Janse van Rensburg

, Longmore

PJ.

1996. Preconditioning to reduce the incidence of face bursts in highly stressed faces. Johannesburg: CSIR Division of Mining Technology. SIMRAC Final Report, Project GAP 030.

Lim

, Martin

CD.

2010. Core disking and its relationship with stress magnitude for Lac Du bonnet granite. Int J Rock Mech Min Sci. 47:254–264. doi: 10.1016/j.ijrmms.2009.11.007

Matsukia

, Kaga

, Tsuda

, Yokoyama

2004. Determination of three dimensional in situ stress from core discing based on analysis of principal tensile stress. Int J Rock Mech Min Sci. 41:1167–1190. doi: 10.1016/j.ijrmms.2004.05.002

Rorke

, Brenchley

, Van Rensburg

AJ.

1989. Preliminary preconditioning results obtained at West Driefontein. Johannesburg: Chamber of Mines. Rock mechanics internal report No. 548.

Rorke

, Cross

, Van Antwerpen

HEF

, Noble

1990. The mining of a small up-dip remnant with the aid of preconditioning blasts. International Deep Mining Conference, Technical Challenges in Deep-level Mining. Johannesburg: SAIMM.

Sengani

, Zvarivadza

2017. Review of pre-conditioning practice in mechanized deep to ultra-deep level gold mining. In: 26th International Symposium on Mine Planning and Equipment Selection (MPES2017); August 29–31 2017; Luleå. p. 113–127.

Stacey

, Wesseloo

2012. Application of indirect stress measurement techniques (non strain gauge based technology) to quantify stress environments in mines. Johannesburg. SIMRAC Report number: GAP 858, p. 1-68.

10.

Toper

AZ.

2002. Destressing / preconditioning to control rock bursts in South African deep-level gold mines. Int. Seminar on Deep and High-Stress Mining. November 2002; Perth: Australian Centre for Geomechanics.

11.

Toper

AZ.

2003. The effect of blasting on the rockmass for designing the most effective preconditioning blasts in deep level gold mines [PhD thesis]. South Africa: University of the Witwatersrand Johannesburg, School of Mining Engineering.