Rock fall trajectory field testing, model simulations and considerations for steep slope design in hard rock

Abstract

Newcrest Mining Limited open pit operations at Telfer (Western Australia) have excavated steep slopes. Current and future planned mine designs also intend to implement steep slopes in order to maintain profitable ore to waste strip ratios. When not adequately considered in the design process, rock falls can present a significant hazard in open pit mines. The management of rock fall hazards becomes particularly vital for steep slopes. Numerical models are often used to assess the effectiveness of benched slope designs or rock fall barriers to minimise risk to personnel or equipment. Commonly used numerical modelling software and simulation impact theories include: • 'RocFall'-two-dimensional lumped-mass impact model (2DLM). • 'Trajec3D'-three-dimensional rigid body impact model (3DRB). Numerical models use coefficients of restitution to characterise the amount of energy lost due to the inelastic deformation during the collision of a rock with the slope or bench. The input parameters are vastly different for 2DLM and 3DRB and they are seldom calibrated with any site-specific rock fall case studies or field test data during project feasibility studies, and often remain uncalibrated through the operating life of the mine. In order to best manage rock fall hazards for steep slopes through design, a series of rock fall trajectory field tests were carried out to facilitate the development of calibrated 2DLM and 3DRB numerical models. The calibrated models were then utilised to assess the effectiveness of various slope design geometries. The influence of model selection was found to have a significant impact upon the results. This paper compares rock fall trajectory predictions obtained from calibrated 2DLM and 3DRB models for steep slope designs in hard rock.

Effects of Wildfire on Rockfall Occurrence: A Review through Actual Cases in Spain

“…Among the input parameters when performing numerical simulations of rockfalls are the rockfall detachment areas, starting velocity of the boulders, a digital terrain model (DTM) and data of the coefficients of dynamic rolling friction, and of normal and tangential energy restitution used to simulate the loss of energy when rolling and at impact points. The most important is the restitution [91][92][93] and the dynamic friction [33,94] coefficients. Restitution coefficient (R) represents the ratio of pre-impact and post-impact velocity between the boulder and soil, and it is subdivided into tangential (Rt) and normal (Rn) components.…”

Evaluation of rockfalls at a historical settlement area in the Ihlara valley (Cappadocia, Turkey) using different methods

“…Site-specific restitution coefficients can be estimated directly from laboratory or field tests, back analysis of falling blocks, or using theoretical estimation methods (Bozzolo and Pamini 1986;Kobayashi et al 1990;Evans and Hungr 1993;Budetta and Santo 1994;Robotham et al 1995;Chau et al 2002). The most common method is to estimate them from the back analysis of measured rock paths and end locations during the field tests of rockfall trajectory (Bar et al 2016).…”

“…However, in the active mitigation, rockfall event occurrence is prevented from the source zone by rock bolting, slope retention systems, shotcrete, altering slope geometry, dewatering the slope, and revegetation. Several researchers (Ritchie 1963;Pierson et al 1990;Pantelidis 2009 andBar et al 2016) have outlined some guidelines for designing passive measures.…”

Application of Remote Sensing Data for Evaluation of Rockfall Potential within a Quarry Slope

“…An established method to assess the hazard posed by rockfalls is the use of probabilistic rockfall trajectory analysis [38,39]. A probabilistic approach is adopted to consider both ontic and epistemic Figure 6.…”

“…COR are defined in the normal direction (CORN) and tangential (CORT) to the slope. They are used to account for energy lost due to the inelastic deformation during the collision of a rock with the slope or bench [39]. COR are key parameters for rockfall modelling, and it is necessary to use engineering judgement when selecting appropriate values from literature, especially given the inherent difficulties of defining them empirically through field testing [9,10,40].…”