Johan Wesseloo

Discrimination of Mine Seismic Events and Blasts Using the Fisher Classifier, Naive Bayesian Classifier and Logistic Regression

Seismic events and blasts generate seismic waveforms that have different characteristics. The challenge to confidently differentiate these two signatures is complex and requires the integration of physical and statistical techniques. In this paper, the different characteristics of blasts and seismic events were investigated by comparing probability density distributions of different parameters. Five typical parameters of blasts and events and the probability density functions of blast time, as well as probability density functions of origin time difference for neighbouring blasts were extracted as discriminant indicators. The Fisher classifier, naive Bayesian classifier and logistic regression were used to establish discriminators. Databases from three Australian and Canadian mines were established for training, calibrating and testing the discriminant models. The classification performances and discriminant precision of the three statistical techniques were discussed and compared. The proposed discriminators have explicit and simple functions which can be easily used by workers in mines or researchers. Back-test, applied results, cross-validated results and analysis of receiver operating characteristic curves in different mines have shown that the discriminator for one of the mines has a reasonably good discriminating performance.

Interpretation of seismic data and numerical modelling of fault reactivation at El Teniente, Reservas Norte sector

Abstract Reservas Norte (RENO) is one of the panel caving sectors of El Teniente mines, owned by Codelco Chile. The sector has experienced mine induced seismicity for many years. The work presented in this paper focuses on seismic activity recorded between the period from January 2004 to July 2008. The interpretation of the seismic data revealed that the sources of elevated seismic hazard (large events) at RENO during this period could be attributed to four major geological structures: Falla G, Falla F, Falla C, Falla N1. In particular, the seismic response of the four structures to undercut blasting activities is examined in detail. The use of numerical modelling has shown that it is possible to simulate this response after calibrating the model against the cumulative seismic moment released by the faults, as mining advances towards them. This calibrated numerical model can then be used to forecast future seismic responses. The main product of this work is a tool that can be used to rank different undercutting rates and geometries in terms of seismic hazard.

An interpretation of ground support capacity submitted to dynamic loading

Abstract Rockburst risk is an increasing problem in underground mining worldwide, as the general trend is for mines to operate in deeper environments. In most mines affected by seismicity, the first line of defence to mitigate the potential consequences of rockburst is to install dynamic resistant ground support systems. The assessment of ground support capacity when submitted to dynamic loading has been the subject of intensive research over the last two decades. In particular, drop tests were developed to investigate the capacity of support elements while the performance of various support systems was examined by simulating rockbursts with carefully designed blasts. The above research has yet to yield an accepted method to determine the dynamic capacity of ground support. In this paper, the published results from many of the above tests are compiled and practical observations are made regarding the dynamic capacity of ground support systems.

Empirical methods for assessment of seismic system sensitivity

Abstract One of the basic performance characteristics of the seismic system is its sensitivity. An appreciation of the spatial variation of mmin is important for the correct interpretation of seismic data and the planning of future expansion of the seismic system. This paper will discuss the empirical evaluation of the system sensitivity applied to the data from two Australian mines. The method discussed here is reliant on enough seismic data being available and is per se not applicable to greenfields sites. A gridless method for the evaluation of mmin with respect to the distance to sensors is proposed as a stable and relatively easy first order approach to the evaluation of the system sensitivity that overcomes some of the problems of the other methods. This method is easy to understand and facilitate the conceptualisation of the influence of the sensor locations on the system sensitivity.

The Spatial Assessment of the Current Seismic Hazard State for Hard Rock Underground Mines

Mining-induced seismic hazard assessment is an important component in the management of safety and financial risk in mines. As the seismic hazard is a response to the mining activity, it is non-stationary and variable both in space and time. This paper presents an approach for implementing a probabilistic seismic hazard assessment to assess the current hazard state of a mine. Each of the components of the probabilistic seismic hazard assessment is considered within the context of hard rock underground mines. The focus of this paper is the assessment of the in-mine hazard distribution and does not consider the hazard to nearby public or structures. A rating system and methodologies to present hazard maps, for the purpose of communicating to different stakeholders in the mine, i.e. mine managers, technical personnel and the work force, are developed. The approach allows one to update the assessment with relative ease and within short time periods as new data become available, enabling the monitoring of the spatial and temporal change in the seismic hazard.

Temporal Delineation and Quantification of Short Term Clustered Mining Seismicity

The assessment of the temporal characteristics of seismicity is fundamental to understanding and quantifying the seismic hazard associated with mining, the effectiveness of strategies and tactics used to manage seismic hazard, and the relationship between seismicity and changes to the mining environment. This article aims to improve the accuracy and precision in which the temporal dimension of seismic responses can be quantified and delineated. We present a review and discussion on the occurrence of time-dependent mining seismicity with a specific focus on temporal modelling and the modified Omori law (MOL). This forms the basis for the development of a simple weighted metric that allows for the consistent temporal delineation and quantification of a seismic response. The optimisation of this metric allows for the selection of the most appropriate modelling interval given the temporal attributes of time-dependent mining seismicity. We evaluate the performance weighted metric for the modelling of a synthetic seismic dataset. This assessment shows that seismic responses can be quantified and delineated by the MOL, with reasonable accuracy and precision, when the modelling is optimised by evaluating the weighted MLE metric. Furthermore, this assessment highlights that decreased weighted MLE metric performance can be expected if there is a lack of contrast between the temporal characteristics of events associated with different processes.

A Reconsideration of the Extension Strain Criterion for Fracture and Failure of Rock

The complex behaviours of rocks and rock masses have presented paradoxes to the rock engineer, including the fracturing of seemingly strong rock under low stress conditions, which often occurs near excavation boundaries. The extension strain criterion was presented as a fracture initiation criterion under these conditions (Stacey in Int J Rock Mech Min Sci 18:469–474, 1981). This criterion has been used successfully by some and criticised by others. In this paper, we review the literature on the extension strain criterion and present a case for the correct interpretation of the criterion and the conditions suitable for its use. We argue that the extension strain criterion can also be used to provide an indication of damage level under conditions of relatively low confining stress. We also present an augmentation of the criterion, the ultimate extension strain, which is applicable under extensional loading conditions when σ2 is similar in magnitude to σ1.