Derek Apel

Thermal characterisation of a lightweight mortar containing expanded perlite for underground insulation

This paper aims to investigate the use of expanded perlite in mortar, for further application of shotcrete to thermal insulation of underground mines. Mixes were designed according to the typical proportions of underground shotcrete, with the sand volumetrically substituted by expanded perlite. Tests of samples were conducted at four ages. Transient plane source technique was utilised to measure the thermal properties. The results showed reduced weight, decreased thermal conductivity, deteriorated thermal diffusivity, and sacrificed mechanical strength with perlite addition. Experimental data analysis and explanation in this paper would establish useful fundamentals for further application of expanded perlite to underground shotcrete.

A Principal Component Analysis/Fuzzy Comprehensive Evaluation for Rockburst Potential in Kimberlite

Kimberlite is an igneous rock which sometimes bears diamonds. Most of the diamonds mined in the world today are found in kimberlite ores. Burst potential in kimberlite has not been investigated, because kimberlite is mostly mined using open-pit mining, which poses very little threat of rock bursting. However, as the mining depth keeps increasing, the mines convert to underground mining methods, which can pose a threat of rock bursting in kimberlite. This paper focuses on the burst potential of kimberlite at a diamond mine in northern Canada. A combined model with the methods of principal component analysis (PCA) and fuzzy comprehensive evaluation (FCE) is developed to process data from 12 different locations in kimberlite pipes. Based on calculated 12 fuzzy evaluation vectors, 8 locations show a moderate burst potential, 2 locations show no burst potential, and 2 locations show strong and violent burst potential, respectively. Using statistical principles, a Mahalanobis distance is adopted to build a comprehensive fuzzy evaluation vector for the whole mine and the final evaluation for burst potential is moderate, which is verified by a practical rockbursting situation at mine site.

Rockbursting Potential of Kimberlite: A Case Study of Diavik Diamond Mine

The research described in this paper provides information about the rockbursting potential of kimberlite. Kimberlite is a diamond-bearing rock found in deposits around the world including northern Canada. This paper outlines three methods for the prediction of rockbursts based on the properties of a rock. The methods include the: strain energy index, strain energy density, and rock brittleness. Kimberlite samples collected from Diavik, a diamond mine in northern Canada, were tested to define the rock’s uniaxial compressive strength, tensile strength, and hysteresis loop. The samples were separated into sub-rock types based on their descriptions from the mine geologists. The results indicate that it is possible to produce rockbursts in kimberlite. It was also observed that the sub-rock types had a range of rockbursting properties. Some types of kimberlite exhibited little to no potential for producing bursts, while other types potentially could produce violent bursts. The diverse nature of kimberlite indicates that the rockbursting properties of the rock should not be generalized and are dependent on the sub-rock type being encountered.

Cylindrical models of heat flow and thermo-elastic stresses in underground tunnels

Purpose The trapped geothermal heat in the infinite rock mass through which mine tunnels are excavated is a great threat to the safety of personnel and mine operating equipment in deep underground hot mines. In order to lessen the temperature inside the tunnel a considerable amount of energy is being spent by the way of using ventilation and cooling systems to dissipate the heat. However, operational costs of the system rise quite considerably, especially as the mines get deeper. Shotcrete is used both as a structural lining and as an effective insulation to reduce the heat load on the ventilation and cooling system within such tunnels. The paper aims to discuss these issues. Design/methodology/approach In order to analyse this problem of heat flow and thermal stresses and their time dependent pattern, several cylindrical models, in both analytical and numerical forms, are discussed and compared in this paper. Findings This study shows the validation of ABAQUS® software to predict the time dependent temperature and the thermal stresses in mine tunnels through the comparisons with the available analytical models. Further, thermal insulation effects of shotcrete are also evaluated with these theoretical models and it is found that all the models gave results in close agreements with one another. Originality/value Therefore, this study provides the theoretical proof for advantages in applying shotcrete as the thermal insulation layer in underground mines.

Full Three-dimensional Finite Element Analysis of the Stress Redistribution in Mine Structural Pillar

The assessment of the magnitudes and directions of the in situ and mining induced stresses is a vital part of an underground excavation design. In this study, the finite element method is used to develop and establish a full three-dimensional numerical model using Abaqus/Standard (Dassault Systemes) software to evaluate the stress redistribution and the ground stability in main production level of an underground hard rock mine located in Northern Canada. The in-situ stresses are calculated based on the unit weight of the overburden rock. The ratio of the average horizontal stress to vertical stress is assumed to be 1.5. This value is selected based on the average stress ratios obtained from the neighboring mines. The behavior of the rock is assumed to be elasto-plastic. To verify and calibrate the numerical model, the obtained displacements values are compared with the values obtained from the ground movement monitors installed in this area. Based on the results of the numerical model, it was concluded that benching of the floor in the 7340E access drift by an additional 2m would increase the zones of failure in the studied pillar. Moreover, the zones of failure in the adjacent tunnels which were inside of the zone of influence of the 7340E access drift would be increased dramatically.

Comparison of empirical and numerical methods in tunnel stability analysis

The stability of a tunnel can be evaluated using mathematical solutions, empirical methods, or numerical modelling. Mathematical solutions are precise methods; however the need to conduct mathematical calculations usually decreases the users desire to use this method. Empirical methods are based on the experience gathered by researchers in various parts of the world whereas numerical modelling utilises computing power and, using various modelling techniques, can be a precise way of solving very complex problems. In this method the environment and the geometry can be set by the user. This method allows the user to conduct sensitivity analysis. In this article, empirical methods and numerical modelling using UDEC software were used to conduct a stability analysis of the access tunnel at the Shahriar dam crest, which was one of the most important tunnels of this project. In addition, numerical modelling was used to predict the stresses and deformations around the perimeter of the tunnel, and select the most suitable ground support system. The results obtained from both methods were compared for selection of the best suited support system. The results indicated that the empirical methods presented similar results to the results of numerical modelling at the first stages of tunnel design in jointed rocks. Therefore, in the absence of sufficient information for numerical analysis, the results of the empirical method can be used for this project.

The Effects of Mine Fog and Vibration Sources on an Experimental Ground Convergence Monitor

Falls of ground are a leading source of worker injury and fatality indicating a persistent need for advances in ground monitoring technology. The high-resolution target movement monitor (HRTMM) is an experimental convergence monitor utilising a digital camera and custom software to track the position of one or more lasers across a target. The potential uses of the HRTMM include convergence monitoring in underground mining or tunnelling applications. For this article, the HRTMM was installed in an underground lead mine near active operations to test its response to three aspects of the mining environment: the ability of the monitor to survive intense blasting vibrations; error from the vibrations of close-proximity heavy equipment; and mine fog error. Improvements to the monitor design are identified from the mine blast test, the measurement error from light fog is determined, and vibrations from nearby equipment are shown to be inconsequential to convergence monitoring activities with the HRTMM.

Evaluation of burst liability in kimberlite using support vector machine

Due to the complex mechanisms of rockburst, there is no current effective method to reliably predict these events. A statistical learning method, support vector machine (SVM), is employed in this paper for kimberlite burst prediction. Four indicators

Jet grouting: mathematical model to predict soilcrete column diameter - part I

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