深部原位岩石力学构想与初步探索

Conceptualization and preliminary research on deep in situ rock mechanics

深部资源开发的基础是研究深地科学规律,关键是探明不同赋存深度原位环境对岩石物理力学行为影响的差异性规律。适用于浅部资源开采的岩石力学实验与理论研究很难充分考虑不同深度原位赋存环境对岩石物理力学特征和工程的影响。提出"深部原位岩石力学"构想的定义和内涵,利用取自松科二井同一地质区域的10个不同深度(1 000~6 400 m)的岩芯研究了不同赋存深度下岩石力学行为的差异性变化特征,并提出了原位应力恢复重构方法近似模拟了不同深度原位应力对岩石力学参数的影响规律。不同深度岩石的单轴压缩实验表明岩石力学参数随深度呈现明显的非线性变化,不能假设为常数。考虑不同深度地应力影响的常规三轴实验表明赋存地应力使得不同深度岩石的力学参数差异性增大,且力学参数随深度的非线性变化规律与单轴压缩条件下显著不同。模拟不同深度原位应力影响的原位应力恢复重构实验结果显示在不同赋存深度原位应力影响下岩石力学参数均随深度增加呈现更加显著的非线性变化;模拟不同深度原位应力影响的应力恢复重构实验的岩石弹性模量和峰值强度均比考虑不同深度地应力影响的常规三轴实验结果大且与深度之间的关系为对数函数,峰后应变软化变形特征更加凸显;特别是深度超过4 800 m后,不同赋存深度原位应力影响下岩石泊松比、应变硬化模量、峰后跌落模量的差异性特征更加明显。该研究将为探索深地科学规律、提升深部资源获取能力提供支撑。

Deep earth science is the basic of deep resource exploitation. One critical challenge is to ascertain the physical and mechanical behaviours of rocks from different depths under in situ geological conditions. Rock mechanical experiments and theoretical studies suitable for shallow resource mining are difficult to consider the effects of deep in situ geological conditions of different buried depths on the rock physical and mechanical characteristics and engineering. This paper puts forward the concept and research content of"deep in situ rock mechanics". Using rock cores collected from 10 different depths(1 000 m to 6 400 m) of Songke second well,the different characteristics of rock mechanical behaviors at different buried depths are studied. An in situ stress restoration and reconstruction method is proposed to approximately simulate the influence of in situ geostress on rock physical and mechanical parameters. Uniaxial compression tests indicate that rock mechanical parameters increase nonlinearly with increasing the buried depth and hence,cannot be treated as constants. Triaxial compression experimental results manifest that rock mechanical parameters vary more obviously with the buried depth due to the geostress,which is different from those under uniaxial compression. Rock mechanical tests retaining the in situ geological condition suggest that the rock mechanical parameters can present more obvious nonlinear behaviors with increasing the buried depth in the case of geostress restoration and reconstruction. The peak strength and Young’s modulus in the in situ stress restoration and reconstruction tests,showing a logarithmic function relationship with the buried depth,are larger than the results in the triaxial compression tests. Also,the post peak strain softening behavior in the in situ stress restoration and reconstruction tests is more obvious than that in the triaxial compression tests. Especially,when the burial depth exceeds 4 800 m,the influences of in situ stress restoration and reconstruction on Poisson’s ratio,strain hardening modulus and post peak are more remarkable. This research can provide support for exploring deep scientific laws and improving deep resource acquisition capabilities.