炭质千枚岩隧道瓦斯生成及运移规律研究

Carbonaceous phyllite is one of the most common formation lithology during the tunnel construction in China's western region. Gas disasters caused by the carbonaceous phyllite lead to constant loss of personnel and property and threaten the construction safety. The mechanism of gas generation and migration in carbonaceous phyllite while tunnel crossing is a key scientific issue that needs to be solved. On the basis of the analysis of organic matter, mineral composition and biomarker of carbonaceous phyllite with different gas content, the purpose of this project is to identify the component factors and degree that affect the gas generation and define the gas occurrence in carbonaceous phyllite through gas adsorption experiment with the combined influence of multiple factors. Rock properties under varied gas pressure will be testd and the constitutive model of deformation and destruction of carbonaceous phyllite with gas will be established based on the principle of energy conservation and rock damage mechanics. Combining with test of pore structure and microscopic characteristics, the physical and structural changes of the carbonaceous phyllite with gas will be obtained. And on this basis, the evolution law of the stress field and crack field of carbonaceous phyllite with the tunnel crossing can be studied. The gas seepage transport equation of rock mass can be established through experiments. Then the contour maps of permeability during tunneling can be calculated and gas accumulation area can be predicted, which provide theoretical support to optimize the gas protection measures of the tunnel and ensure the safety construction of tunnels with carbonaceous phyllite.

炭质千枚岩是我国西部地区隧道工程建设最常见的地层岩性之一，其引起的隧道瓦斯灾害不断造成人员和财产损失，给隧道建设带来重大安全隐患。其中，炭质千枚岩隧道瓦斯生成及运移规律是亟需解决的关键科学问题。本项目旨在不同瓦斯含量炭质千枚岩有机质、矿物成分和生物标志化合物分析基础上，通过多因素综合影响下瓦斯吸附试验，识别影响炭质千枚岩瓦斯生成的组分因素及影响大小，明确炭质千枚岩地层瓦斯赋存特征；开展不同瓦斯压力条件下岩体物性测试，依据能量守恒和岩石损伤力学原理建立炭质千枚岩变形破坏本构模型，结合岩体孔隙结构和细观特征检测，获得瓦斯作用下炭质千枚岩物性和结构变化规律；在此基础上，研究隧道穿越炭质千枚岩地层岩体应力场、裂隙场的演化规律，实验建立岩体瓦斯渗流运移方程，计算隧道掘进过程中瓦斯真实渗透率的等值线分布图，预测瓦斯富集区，为优化隧道瓦斯防护措施，保障炭质千枚岩隧道施工安全提供理论支撑。

炭质千枚岩地层的瓦斯灾害给隧道建设带来重大安全隐患，不断造成人员和财产损失。项目针对我国西部山区隧道穿越炭质千枚岩地层中频发的瓦斯灾害问题，开展了炭质千枚岩瓦斯生成及赋存特性影响、炭质千枚岩物性和结构特征、炭质千枚岩隧道瓦斯运移富集规律等方面的研究。结果表明：四川炭质千枚岩等变质岩主要发育区为川西高原，研究区域炭质千枚岩富含有机质，整体处于成熟~高成熟阶段，是具有良好生烃能力的烃源岩，具备有机作用生成瓦斯气体的能力；结合地层中赋存的瓦斯气体碳同位素δ13C1测试值在-10.7~-36.5，确定炭质千枚岩地层中瓦斯属于有机成因与无机成因的混合气。研究区域炭质千枚岩平均孔隙体积7.28×10-3cm³/g，其中微孔占比28.63%，中孔占比36.67%，大孔占比34.70%，渗透系数为0.001~0.004m/d，属于低孔、低渗地层；不同区域碳质千枚岩样品矿物成分相似，含量存在一定差异，最大吸附量在0.059-0.073mmol/g区间波动，与页岩相似，约为煤层最大吸附量的1/22，具有一定的吸附能力和解吸能力。台阶法施工中掌子面和台阶处瓦斯浓度差异较大，当上台阶长度为5-20m左右时，既能顾及到射流对上台阶掌子面冲击力，又能控制下台阶前涡流区大小和射流所卷吸的空气量；风管管口距掌子面5-10m左右最佳，对于上下断面通风效果均有改善，同时风管应沿侧壁布设较佳；通过合理的布置掌子面长度、风管位置和风量能够满足瓦斯稀释的要求。除岩体本身性质外，断层及裂隙发育程度和隧道埋深大小对炭质千枚岩隧道瓦斯气体的运移和储集影响较大。隧道离断层越近，裂隙越发育，开挖时有害气体逸出浓度越高；隧道埋深越大，隧道开挖过程中，遭遇有害气体逸出浓度也越高。