循环冲击下弱风化岩石力学特性与渗透率演化
Mechanical properties and permeability evolution of weakly weathered rocks under cyclic impact
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摘要: 低渗透弱风化花岗岩型稀土矿床中蕴含大量的中重型稀土，但矿体渗透性严重影响溶浸效率，提出利用爆炸冲击载荷对稀土矿体产生多次扰动，在确保矿体保持稳定性的前提下使内部细观结构发生变化，进而提高矿体渗透性。为探究爆炸冲击载荷多次扰动下弱风化花岗岩的力学特性及渗透系数的变化，利用Hopkinson冲击试验机、RMT-150C液压伺服试验机、核磁共振仪，对试件进行逐级循环冲击实验和冲击后的静态压缩实验，并测量试件的孔隙度与渗透系数。研究结果表明:逐级循环冲击下弱风化花岗岩存在裂隙压密阶段，但不明显;裂纹扩展阶段存在明显的应力松弛平台，且随冲击速度的增加愈加明显;动态峰值应力与临界应变随冲击速度的增加呈递增趋势;冲击后的静力学特性表现为随着冲击次数的增加，裂纹压密阶段持续时间增加，弹性阶段持续时间减少，裂纹起裂应力σci、裂纹损伤应力σcd、单轴抗压峰值强度σf逐渐下降，临界应变逐渐增大。试件中含有小中大3种孔隙类型，在逐级循环冲击下整体表现为中等孔隙占比增加，小型、大型孔隙占比基本不变，有效孔隙度逐渐增加，第1次冲击后这种变化较为明显。弱风化花岗岩经过3次冲击后，渗透系数达到最大，长期强度下降约13%。Abstract: Weathered rare earth ore contains a large amount of mediumheavy rare earth,the permeability of ore body seriously affects the mining efficiency.This paper proposes that the use of the explosive impact load can cause multiple disturbances to the rare earth ore body,change the internal microstructure,improve the permeability and keep the ore body stable.In order to explore the mechanical properties and permeability coefficient of weakly weathered granite under multiple perturbations from blast impact load,the Hopkinson impact testing machine,RMT-150C hydraulic servo testing machine and Nuclear Magnetic Resonance were used to respectively carry out a step by step cyclic impact test and static compress test (after the disturbance).The porosity and permeability coefficient of the specimen were measured.The results of research show that a fracture compaction stage exists in weakly weathered granite under cyclic impact,but it is not obvious.The stress relaxation platform exists in the crack propagation stage of weakly weathered rock under a step by step cyclic impact test,and it becomes more obvious with the increase of impact speed.The peak stress increases with the increase of impact velocity.At the aspect of static characteristics (after impact),the duration of crack compaction stage increases and the elastic stage decreases,the crack initiation stress σci,crack damaging stress σcd and uniaxial compressive peak strength σf decrease,and the critical strain increases gradually with the increase of impact times.There are three types of pores in the test specimen,the number of medium pores increase under the step by step loading,the number of small and large pores keep unchanged.After three impacts,the effective porosity and permeability coefficient of the specimen were greater than the initial value,and the peak stress is reduced by about 13%.The aim of increasing permeability based on the stability of ore body is realized.
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Keywords:
- mechanical property /
- permeability /
- weakly weathered granite /
- cycle impact /
- explosive impact load
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