Use of joint trace data to evaluate stability of mining excavations, and validation against underground observations (original) (raw)
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The RockRisk project: rockfall risk quantification and prevention
2017
Rockfalls are frequent instability processes in road cuts, open pit mines and quarries, steep slopes and cliffs. The orientation and persistence of joints within the rock mass define the size of the kinematically unstable rock volumes and determine the way how the detached mass be-comes fragmented upon the impact on the ground surface. Knowledge of the size and trajectory of the blocks resulting from fragmentation is critical for calculating the impact probability and intensity, the vulnerability the exposed elements and the performance of protection structures. In this contribution we summarize the main goals and achievements of the RockRisk project. We focused on the characterization of the rockfall fragmentation by means of the analysis of the fracture pattern of intact rock masses, the development of a fragmentation model and its integration into rockfall propagation analysis. The ultimate goal of the project is to quantify risk due to rockfalls and develop tools for the improve...
Experimental and Theoretical Studies to Improve Rock Fall Analysis and Protection Work Design
Rock Mechanics and Rock Engineering, 2004
This paper reports an analysis procedure for the evaluation of the features of the motion of blocks detaching from a steep rock wall and traveling down the slope below. Starting from the execution of real scale rock fall tests, carried out on two slopes having different morphology and lithology, the paper describes the methodology used for test interpretation and a procedure for the evaluation of the parameters best suited to the description of rock fall motion. The influence of the parameters assessed on the prediction of the rock fall trajectory was also investigated using twodimensional and three-dimensional numerical models. These models were calibrated by means of a back analysis of the in situ tests, which also allowed the evaluation of the uncertainties involved in the parameters experimentally estimated.
Numerical analysis of rockfall hazard in open pit coal mines
Rockfalls are a signifi cant safety hazard in open pit mines and underground mine entries from open cut highwalls that need to be rigorously managed when designing portal entries for punch longwalls. The installation of restraining nets is a common practice to mitigate this hazard. The protective system however does not totally eliminate the rockfall hazard as blocks can still detach and fall in-between the net and the highwall. In such cases it is of prime importance to predict the rockfall trajectories and velocities behind the protective net in order to properly map and assess the residual hazard. An integrated approach combining fi eld testing and DEM is currently being developed for which site specifi c knowledge of the fundamental characteristics of rockfalls in open pit coal mines is necessary. This work presents numerical analyses from which estimations of rockfall motion, trajectories, arrest zones and potential impacting energy on the protection structure are worked out. The study entails the estimation of the size distribution of unstable block fi rst and then the simulation of their trajectories. The former requires an accurate description of the rock mass structure. By combining digital 3D photogrammetry analyses with Discrete Fracture Network modelling it is possible to generate a polyhedral model of the rock mass structure. A modeller capable to automatically identify complex polyhedra (rock blocks) has been used to represent a rock mass with fi nite persistence discontinuities. Size distribution of unstable blocks and trajectories are assessed performing Monte Carlo analyses where unstable blocks are detected using the key-block method for each realisation. Results are compared with the actual history of rockfall events. This site-specifi c knowledge will later be used for residual hazard assessment (i.e. trajectories and fi nal velocities behind protective nets).
Analysis and prediction of rockfalls using a mathematical model
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995
This paper deals with the study of rockfalls using a mathematical model, codified for computer use. Called CADMA, it allows predictions to be made of fall trajectories and of the relevant parameters (energy, height of bounce, run out distance of the falling blocks) for the design of remedial works. Designed with the experience gained from several in situ tests, this
ROckfall risk MAnagement assessment: the RO.MA. approach
Natural Hazards, 2012
The analysis of risk for vehicles and drivers as a result of rockfall on a road is relevant to design management in geotechnical engineering. This process is very complex due to the large number of parameters involved. In this paper, we discuss risk analysis and management procedures for roads subject to rockfall phenomena. To this aims, we are proposing a quantitative method (the RO.MA. approach). We developed an abacus to define the threshold values of acceptable rockfall risk for a given road. Rockfall risk is calculated using an Event Tree approach and compared with the abacus thresholds to evaluate road safety and the need for additional protective measures to reduce the risk to an acceptable level. The approach was successfully applied at a test site located in Bard,
A Design Scenario Approach for Choosing Protection Works against Rockfall Phenomena
Remote Sensing
Proximity remote sensing techniques, both land- and drone-based, allow for a significant improvement of the quality and quantity of raw data employed in the analysis of rockfall phenomena. In particular, the large amount of data these techniques can provide allows for the use of probabilistic approaches to rock mass characterization, with particular reference to block volume and shape definition. These, in return, are key parameters required for a proper rockfall hazard assessment and the optimization of countermeasures design. This study aims at providing a sort of guide, starting from the data gathering phase to the processing, up to the implementation of the outputs in a probabilistic-based scenario, which is able to associate a probability of not being exceeded with total kinetic energy values. By doing so, we were able to introduce a new approach for the choice of design parameters and the evaluation of the effectiveness of mitigation techniques. For this purpose, a suitable ca...
2007
Probabilistic design is gaining wider acceptance in the rock engineering community since it allows more rigorous determination of risk relating to ground fall or excavation instability. Risk analysis can be conducted by various means, but the basis is formed by either objectively or subjectively determining probability of occurrence of an event. In the case of rock engineering, this event is either instability or excavation failure. Rock mass classification systems provide objective analysis of data collected on a typically subjective basis that also relate closely to excavation stability. A probabilistic analysis technique is presented that uses statistical distributions of rock mass and material properties, ground support fixture specifications, stress conditions, opening geometry, and ground support installation quality to more rigorously determine probability of failure for an underground opening and the subsequent risk to personnel.
Rockfall characterisation and structural protection – a review
Natural Hazards and Earth System Science, 2011
Rockfall is an extremely rapid process involving long travel distances. Due to these features, when an event occurs, the ability to take evasive action is practically zero and, thus, the risk of injury or loss of life is high. Damage to buildings and infrastructure is quite likely. In many cases, therefore, suitable protection measures are necessary. This contribution provides an overview of previous and current research on the main topics related to rockfall. It covers the onset of rockfall and runout modelling approaches, as well as hazard zoning and protection measures. It is the aim of this article to provide an in-depth knowledge base for researchers and practitioners involved in projects dealing with the rockfall protection of infrastructures, who may work in the fields of civil or environmental engineering, risk and safety, the earth and natural sciences.
Rock fall hazard assessment: from qualitative to quantitative failure probability
A new method (HGP) is proposed to estimate the failure probability of potentially unstable rock masses in a homogenous area, as a function of time. It is based on both geomechanical and historical approaches: the first one is aimed to classify the rock masses according to their relative failure probability, but the time factor can not be approached by a mechanical analysis; the second one to estimate the mean expected rock fall number in the studied area, for the considered period and for different volume classes. This rock fall frequency can be estimated from a rock fall inventory, directly or indirectly using a power law for the volume distribution. A relation between these frequencies and the erosion rate is established, which allows to approach the former from a paleogeographical study. The failure probabilities can be calculated from the expected total rock fall number in the area, and the numbers of potential rock falls with different relative probabilities. The method is appl...