【作者】 秦阳；

【导师】 肖清华；

【作者基本信息】 西南交通大学 ， 岩土工程， 2013， 硕士

【摘要】 随着我国经济建设的突飞猛进,水利水电、公路铁路等事业也不断发展,相关的地下工程建设日趋复杂,在高地应力条件下地下洞室开挖过程中洞室围岩变形、应力分布及其稳定性变化具有极大的特殊性。如果在大埋深高地应力条件下进行隧洞开挖,其围岩的力学特性及稳定性尤其要密切关注,一旦出现问题则容易影响地下工程安全甚至发生灾难性后果。然而,究竟如何才能准确得出围岩力学行为规律及其与一般条件下的围岩变形及应力二次分布规律有何不同,围岩稳定性分析方法和指标与传统方法有何区别以及区别到底有大,还须做进一步的大力探索和研究。本文以目前世界规模最大的锦屏二级水电站引水隧洞建设工程为背景,综合运用现场调查、理论分析、数值模拟、现场实测等方法与手段,全面系统地研究了围岩动态应力和位移变化规律,并采用多项指标综合评价了高地应力条件下大埋深岩爆高风险隧洞的围岩稳定性。本文的主要研究内容及结论如下：(1)从地质构造、围岩岩性参数指标、围岩分类等方面系统全面地分析了锦屏二级水电站引水隧洞工程区的工程地质条件,结合地质条件对引水隧洞的断面条件和开挖施工方案进行了分析,揭示了锦屏二级水电站引水隧洞具有大断面、大埋深、高地应力以及岩爆高风险等特点。在高地应力条件下开挖洞径达13m的隧洞,由于开挖过程围岩应力重新分布影响,有可能导致应力集中而诱发较为强烈的岩爆,在建设过程将会遭遇极大挑战,必须对其重大难题进行研究。(2)通过对岩爆段岩爆形式的统计分析发现,锦屏二级水电站引水隧洞群岩爆破坏类型主要为剥落型和爆裂型,岩爆主要发生在围岩条件较好的II级围岩且伴随有较大的声响,主要发生在拱顶、拱肩和隧洞边墙。岩爆具有滞后性,离掌子面一定距离的已支护洞段也有可能发生岩爆。(3)选取典型埋深的洞段,运用数值模拟和现场实测等方法,对高地应力条件下隧洞开挖围岩的动态力学行为进行分析后发现,洞周会形成应力松弛而不是应力集中,反之由于应力转移在离洞壁一定深度内会形成应力集中区,围岩的安全稳定系数较低。开挖卸荷后应力将向深部围岩转移,在隧洞的左拱肩和右边墙位置会形成较大的应力集中,从能量的角度看在应力集中区域形成了较大的弹性应变能集中,该区域具有岩爆发生的应力和能量条件。可见高地应力条件下隧洞开挖过程围岩力学特性与一般条件下有所不同。(4)针对不同锚杆长度和不同锚杆预应力值情况,分析了其对围岩稳定性的影响。研究结果表明：锚杆在一定长度范围内随着锚杆长度的增加,洞周围岩位移明显减小,围岩的应力状态得到明显改善,但是超过一定长度后锚杆的作用几乎不变,所以选择过长的锚杆并不能充分发挥锚杆的控制作用,既不经济也不合理。同样增加锚杆预应力也能够有效改善围岩应力状态和控制围岩位移,但是超过一定值后锚杆的控制作用不再明显,也不能充分发挥锚杆的作用。(5)分别从围岩的围岩和应力变化规律、锚杆轴力变化规律、围岩塑性区体积变化规律以及围岩能量释放等多角度分析了不同支护滞后距离对围岩稳定性的影响。研究结果表明,随着支护滞后距离的增大,围岩应力和位移释放不断增大,围岩的自承载能力增加支护抗力减小,围岩的破坏和能量释放增大,围岩的稳定性降低。支护滞后距离为3m-6m时围岩应力和位移释放最为剧烈,且洞周围岩塑性区破坏体积和能量释放率变化最为明显,锚杆轴力的变化幅度也最大,现场应重点关注支护滞后3-6m区间时围岩稳定性的变化情况。在高地应力下进行隧洞开挖时,应及时支护跟进以充分发挥支护结构的加固作用,从而改善围岩力学性态并保证围岩稳定和地下结构安全。更多还原

【Abstract】 With the rapid development of Chinese economy, great development also appears in construction of water conservancy and hydropower, road and rail and so. In the process of underground cavern excavation, stress distribution, surrounding rock deformation and stability would be changed by great specificity. Tunnel excavation in deep and high stress conditions, the mechanical properties and stability of the surrounding rock in particular must be pay close attention to, once there are problems, it is likely to affect the safety of the underground structure even catastrophic consequences. However, it is very difficult to accurately make out the mechanical behavior of surrounding rock and it is not easy to find out the differences of the rock deformation and stress secondary distribution between general conditions and high stress conditions. What’s the difference in the surrounding rock stability analysis methods and indicators with traditional methods, the strong exploration and further research needs to be done.In this paper, taking Jinping Ⅱ Hydropower Station diversion tunnels construction as the engineering background, there is a comprehensive study of the surrounding rock mass dynamic variation rules of the stress and displacement. And using of multiple index comprehensive evaluation to analysis the stability of surrounding rock under high stress rock burst in deep high risk tunnel. The main contents and conclusions are as follows:(1) From the geological conditions, the parameters of surrounding rock, rock classification system, a comprehensive analysis of the diversion tunnels of Jinping Ⅱ hydropower engineering geological conditions of the project area was done, the diversion tunnel section conditions on excavation and construction scheme were analyzed with the geological conditions, revealed Jinping Ⅱ Hydropower Station Diversion Tunnels with large section, large buried depth, high ground stress and high risk of rock burst characteristics. Excavation diameter of up to13m tunnel in high ground stress conditions, the surrounding rock stress redistribution of the excavation process may cause stress concentration and strong rock burst, the construction process will encounter great challenge, we must study the major problem.(2) Based on statistical analysis of the rock burst form in period of rock burst, this paper found that rock burst types are mainly spalling and burst. Rock burst occurred mainly in the surrounding rock conditions Ⅱ with large noise, mainly in arch side wall and the vault of the tunnel. Rock burst has hysteresis, it may occur in the tunnel of a certain distance from the working face which has been supported.(3) Selected the typical depth of the tunnel section, by means of numerical simulation and field measurement method, the analysis of the dynamic mechanical the surrounding rock’s behavior of tunnel excavation in high stress conditions found that around the hole the formation of stress relaxation instead of stress concentration, but because the stress transfer it will form stress concentration zone in the surrounding rock in certain depth from the wall, the safety factor of stability of surrounding rock is lower, but due to the release of stress after excavation unloading, stress will be transferred to the deep surrounding rock, it will form a large stress concentration zone in the left tunnel shoulder and right tunnel arch wall, from the point of view of energy it also formed a large elastic strain energy concentration in the stress concentration region, the region has the rockburst conditions of stress and energy. So the mechanical characteristics of surrounding rock in tunnel excavation process in high stress conditions are different from in the general conditions.(4) Analysis results of effect of increasing length and prestress of bolt on the surrounding rock stability show that, increasing the length of bolt within a certain length can improve the control effect of surrounding rock deformation and improve the stress state of surrounding rock, but with the increasing of the bolt length, bolt role gradually reduced. Using the long bolt can not give full play to bolt action, neither economic nor reasonable. Adding bolt prestressing can effectively control of the surrounding rock deformation and improve the stress state of surrounding rock, but when more than a certain value the control effect will decrease gradually.(5) This paper studied the influence of surrounding rock displacement and stress variation, variation of the bolt axial force,variation of the plastic zone volume and the energy release, the results shows that with the increase of supporting lag distance, the surrounding rock stress and displacement increase. The bearing capacity of surrounding rock increase, support resistance decreases, the surrounding rock failure volume and the energy release increase, the stability of surrounding rock reduce. Supporting lag distance of3m-6m, stress and displacement of surrounding rock release is the most dramatic, and the surrounding rock plastic zone damage volume and energy release rate changed most obviously, variation of axial force of bolt is the largest. We should pay more attention to the variation of surrounding rock when supporting lag distance of3m-6m.In the high stress of tunnel excavation, should be timely support to follow to give full play to the role of the reinforcement of the supporting structure, to improve the mechanical properties of surrounding rock and ensure the stability of surrounding rock and underground structure safety.更多还原