simulation of the effects of thermo insulating

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Simulation of the Effects of Thermo Insulating

Shotcrete on the Energy Consumption of

Ventilation and Cooling Systems at Deep

Underground Mines

Derek Apel, Wei Liu, and Vivek Bindiganavile

University of Alberta

Abstract. As the demand for minerals increases over the world, mining reaches

new depths. As a result, one has to contend with increasing temperatures in

working areas due to geothermal heat trapped in the surrounding rocks. One

consequence of this is an escalating cost related to ventilation and cooling systems

in order to keep the working environment comfortable for miners. It is here that

the application of thermal insulation, which is also mechanically sound, assumes

importance. However, until now, the insulation technique has not been widely

used in hot mines around the world, due to the difficulty in insulation material

selection. The insulation layer on the rock surface of mine openings serves as a

thermo-barrier to reduce the heat flow from the rock to the mine atmosphere.

This paper uses the results of laboratory tests conducted with various mixtures

of thermo insulating shotcretes to find out whether or not insulation of mine

airways would be economically viable for hot underground mines.

Keywords: deep mine, thermal insulation, shotcrete, ventilation.

1 Introduction

Many places around world where the geothermal gradient is high are facing

problems with cooing costs at their underground mines. In order to reduce the air

temperature at their underground workings most of these mines will use some type

of air-conditioning technique or they will try to increase the number of air

exchanges. To further limit the cooling and ventilation costs many mines will use


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the ventilation on demand technique where only the currently used areas are

ventilated. This paper discusses results of numerical simulations on the developed

thermal insulating shotcrete which was sprayed on the inside walls of simulated

underground tunnels. The results have showed that the thermo insulating shotcrete

can achieve excellent heat load reductions which can significantly reduce the

cooling and ventilation costs at hot underground mines.

38 D. Apel, W. Liu, and V. Bindiganavile

2 Preparation of the Samples and Laboratory Results

The results of previously conducted laboratory experiments at the University of

Alberta (Liu, et al. 2011, 2013) reported thermal conductivity reduction of the

shotcrete mixtures which contained perlite. Perlite is a volcanic rock, which has

high moisture content of 2-5%.. During further processing, this rock is heated

above the temperature of 870C (Kramar & Bindiganavile, 2010) which causes the

evaporating water to expand rapidly the rock volume. The final product, although

made of naturally occurring rock, looks similar to the roughly cut Styrofoam chips

(Fig. 1) but unlike the Styrofoam the perlite is non-flammable and will not reliase

Expanded perlite has been widely used in thermal and acoustical insulation, fire

resistance and reduction of concrete product weight (Ciullo, 1996) but has not

been used widely by the mining industry. For the laboratory tests four shotcrete

mixtures with perlite were used (Fig. 2) and also shotcrete samples with no perlite

were used as the benchmark samples for the tests. Therefore in total five different

mixtures were prepared using 0%, 25%, 50%, 75% and 100% replacement ratios

of sand by expanded perlite aggregate (EPA).

The results of these tests illustrated that the thermal conductivity of the samples

was being decreased with the increase of EPA in the samples. However, the while

the thermo insulating properties of the shotcrete were improving with the increase


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of EPA in the samples, the Uniaxial Compressive Strength of the samples was

being decreased with the increase of EPA in the mixtures (Fig. 3). Two different

methods of preparing the samples were used: in first method the shotcrete

ingredients were mixed in the concrete mixer and then they were casted into the

Fig. 1 Expanded Perlite Aggregate

Simulation of the Effects of Thermo Insulating Shotcrete on the Energy Consumption 39

Fig. 2 Shotcrete samples with 25, 50, 75 and 100% EPA

Fig. 3 Effect of EPA on the Thermal Conductivity and UCS of the shotcrete samples


plastic cylinders and in the second method 10 cm layer of shotcre was casted on

wooden panels using dry shotcrete equipment and then the samples were obtained

by diamond coring the 28 day cured shotcrete. Results of tests conducted on

samples obtained from both techniques were almost identical. Although, it should

be pointed out that the results from casted samples were more consistent than the

once obtained from the dry casted shotcrete. This can be attributed to the variation

in water pressure which was applied at the nozzle during casting of the shotcrete

panels.

3 Numerical Simulation

To simulate the effect of the thermoinsulating shotcrete on the cooling costs at

deep underground mines a mine model was constructed using the ABAQUS

software. All the openings were simulated at deep underground metal mine The

tunnel layout of a typical deep underground metal mine in North America was

used as the modeling object. It was assumed that the mine had a rock temperature

of 80 C degrees as similar conditions exist at some of the proposed mining

projects in Arizona (ADMMR).

Fig. 4 Temperature Distribution in the modeled simulation


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simulation covering the mine tunnels with layer of the thermo insulating shotcrete

can significantly reduce the mine head load but this saving is going to be only

significant if the EPA proportions in the shotcrete are high. On the other hand

increasing the EPA content will cause reduction in strength of the shotcrete to a

point where the shotcrete wont be able to serve the dual purpose of the insulator

and rock support system. It should be also pointed out that that the described

simulation was only carried out with scenario where the whole perimeter of the

tunnels was covered with shotcrete where at most of the mining operations the

tunnel floors will stay open.

References

Hall, A.E., Mathews, K.E., Gangal, M.K.: Ventilation and Refrigeration requirements and

costs in deep Canadian mines, Canada Centre for Mineral and Energy Technology

(1984)

ADMMR. Resolution Copper Takes Over. Arizona Mineral Resource Newsletter (38)

(2004),

http://www.admmr.state.az.us/General/Newsletters/

nwsltr2004-06.pdf

ASTM, Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete

Specimens (ASTM C496/C 496M-04), ASTM International (2004a)


ASTM, Standard Specification for Lightweight Aggregates for Insulating Concrete (ASTM

332), ASTM International (2009a)

ASTM, Test Method for Compressive Strength of Cylindrical Concrete Specimens (ASTM

C39/C39M-09a), ASTM International (2009b)

Ciullo, P.A.: Industrial minerals and their uses: a handbook and formulary, p. 52. William

Andrew Publishing (1996)


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simulation of the effects of thermo insulating

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