Blasting-Induced Permeability Enhancement of Ore Deposits Associated with Low-Permeability Weakly Weathered Granites Based on the Split Hopkinson Pressure Bar

Lei Yan,Shenghui Zhang,Jiangchao Liu,Liansheng Liu,Wenhua Yi

doi:10.1155/2018/4267878

Lei Yan, Shenghui Zhang + Show 3 more

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https://doi.org/10.1155/2018/4267878

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Abstract

By utilizing the improved split Hopkinson pressure bar (SHPB) test device, uniaxial, constant-speed cyclic, and variable-speed cyclic impact compression tests were conducted on weakly weathered granite samples. By combining nuclear magnetic resonance (NMR) and triaxial seepage tests, this study investigated the change laws in the mechanical properties, porosity evolution, and permeability coefficients of the samples under cyclic impacts. The results showed that in constant-speed cyclic impacts with increasing impact times, deformation modulus decreased, whilst porosity firstly decreased and then increased. Furthermore, dynamic peak strength firstly increased and then decreased whereas peak strain constantly increased before failure of the samples. In the variable-speed cyclic impacts, as impact times increased, deformation modulus firstly increased and then declined with damage occurring after four impact times. The compaction process weakened and even disappeared with increasing initial porosity. Three types of pores were found in the samples that changed in multiscale under cyclic loading. In general, small pores extended to medium- and large-sized pores. After three variable-speed cyclic impacts, the porosity of the samples was larger than the initial porosity and the permeability coefficient was greater than its initial value. The results demonstrate that the purpose of enhancing permeability and keeping the ore body stable can be achieved by conducting three variable-speed cyclic impacts on the samples.

Highlights

In situ leach mining has numerous advantages as it is a relatively simple process and is low-cost and environmentfriendly
In accordance with a previous study [16], only when the dynamic peak strength was larger than 80% of the uniaxial compressive strength can effective damages be generated in the rocks
If the dynamic peak strength of the samples is lower than 80% of the uniaxial compressive strength, the minimum impact velocity increased

Summary

Introduction

In situ leach mining has numerous advantages as it is a relatively simple process and is low-cost and environmentfriendly. By referring to the permeability enhancement methods proposed for in situ leach mining of low-permeability oil and gas fields, coalbed methane (CBM), and sandstone-type uranium deposits [4,5,6,7,8], the central concept of “blasting with small dosages and precisely controlled time delay” in rare earth ore bodies has been proposed. In this process, blasting stress waves are used to generate multiple dynamic disturbances on the rare earth ore bodies and change the internal mesostructure, enhancing permeability and maintaining ore body stability

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Conclusion