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基于岩体断裂力学的巷道稳定性与锚喷支护机理研究

Study on Tunnel Stability and Reinforcing Mechanism of Bolts and Shotcrete Based on Rock Fracture Mechanics

【作者】 伍佑伦

【导师】 王元汉;

【作者基本信息】 华中科技大学 , 结构工程, 2004, 博士

【摘要】 岩体工程的稳定性是岩体工程中最重要的问题之一,它影响岩体工程的施工进度与掘支成本并且危及施工人员人身安全。但由于岩体的复杂性以及岩体力学理论远远滞后于工程实践,岩体的稳定性一直是没能很好解决的问题。随着我国岩体工程建设的力度加大,岩体力学理论已经远远满足不了岩体工程的需要。岩体是由岩块与不连续面组成的结构体,其破坏往往是不连续面扩展与复合的结果,不连续面在岩体中的分布方式及其本身的形态与力学性能是千差万别的,因此,研究不连续面对岩体力学性能的影响,是目前岩体力学研究的热点与难点。锚喷支护是目前在地下岩体工程中使用最为广泛的支护方式之一,但其对岩体力学性能加强的作用机理却不很明确,需要进行进一步的研究。岩体断裂力学研究岩体不连续面的扩展规律,从而可以从更深入地了解岩体的破坏过程。本文采用了岩体断裂力学的观点,对巷道围岩的破坏方式进行了解释与分析,并对锚喷支护机理进行研究。本文主要完成了以下几方面的工作:(1)结合巷道围岩的受力特点,系统地分析了岩体中不连续面的扩展与复合方式,分析了岩体中的破坏优势不连续面方位,以及受压剪、拉剪作用下岩体不连续面的扩展方式与复合特点。(2)以圆形断面巷道为例,分析了围岩中微不连续面与临空不连续面的受力特点及其开裂方式。从断裂力学的基本理论出发,推导了圆形断面巷道围岩的破坏区大小与深度的理论公式。结果认为,围岩破坏区的大小受巷道断面、地应力、岩石的断裂韧度、不连续面密度、长度与抗剪性能等因素的影响。(3)采用理论分析与数值方法,研究了喷射混凝土支护对围岩不连续面扩展的抑制作用,并进一步应用板裂纹的理论研究了混凝土支护层的破坏方式与处理方法。研究结果认为,混凝土支护对围岩内部不连续面扩展的影响较小,但对临空不连续面扩展的影响却较大。因此,锚喷支护中,混凝土的作用主要是抑制临空不连续面的破坏。混凝土厚度的变化对抑制不连续面的扩展影响较小,但其厚度越大,混凝土所能提供的抵抗围岩膨胀的能力也越大,混凝土层的破坏范围一般受到锚杆的影响,锚杆的间距越小,混凝土层的破坏范围也会越小。(4)通过实验的方式研究了受压作用下临空不连续面的扩展特点以及锚杆的作用,并采用数值方法对研究结果进行了讨论。研究结果表明,临空不连续面存在翼裂 III<WP=4>纹破坏与剪裂纹破坏,不连续面的倾角越大,越容易扩展,小倾角不连续面更容易产生次生裂纹的破坏方式。锚杆的作用,提高了结构体的力学性能,降低了裂纹尖端的应力集中现象,提高了裂纹尖端裂纹的起裂荷载。锚杆并不改变裂纹的起裂角度,但使翼裂纹扩展的方向向深部偏移,从而加大了因翼裂纹而造成的剥离体的厚度,减缓了翼裂纹的扩展速度。数值分析的结果很好地解释了实验中所出现的情况。(5)采用数值方法,研究了锚杆对翼裂纹扩展的抑制作用。结果认为,锚杆对翼裂纹扩展的抑制作用是非常明显的,锚杆的存在使翼裂纹的应力强度因子降低,锚杆的强度与刚度越大,对翼裂纹尖端的应力强度因子减小量也越大。翼裂纹的长度越大,锚杆的作用也越明显。由此可以说明,锚杆可以大大加强岩体的残余强度。(6)提出了理论分析模型,研究了锚杆对拉剪作用下的不连续面的影响。并计算了受拉、剪以及拉剪组合几种状态下锚杆对不连续面尖端应力强度因子的降低情况。研究结果表明,锚杆的安装角度对锚杆的作用的影响较大。锚杆的存在,使不连续面从从简单的受拉或受剪的状态变成了拉剪组合状态,降低了使不连续面破坏的主要因素的影响,从而起到支护作用。(7)综合锚喷支护的特点,分析了锚杆联系链的支护机理,并在地下矿山的采准巷道支护中进行实践应用。结果表明,锚杆联系链在加强混凝土支护强度,加大锚杆支护性能,抑制不连续面的破坏等方面起了很重要的作用。而且其安装方便,使用灵活,支护能力大的特点很适合在地下矿山复杂地质条件下用来替代锚喷网支护。

【Abstract】 Stability of rock mass is one of the most important problems in rock engineering. Itaffects the engineering progress, tunneling and supporting cost, and may concern the safetyof the constructors. Because of the complexity rock mass and that theory falls behind thepractice, the problem has not solved very well yet. With the rapid development of rockengineering in our country, the theories can not satisfy the need of engineering more andmore. Rock mass is a kind of structural one which is composed by rock blocks anddiscontinuities. The failure of rock mass is usually the result of the growth and coalescenceof the discontinuities. The distribution and state of the discontinuities and their mechanicalcharacteristic has much difference. Therefore, the study of the influence of thediscontinuities on the rock mechanics is a focus and difficult problem. Bolts and shotcretesupporting is one of the widely applied methods in underground rock engineering. But theirreinforcing mechanism for the rock mass is not very clear and needs to be further studied.Rock fracture mechanics study the extension pattern of the discontinuities growth andcoalescence, so it can be used to understand the failure process of the surrounding rock massdeeply. Based the viewpoints of rock fracture mechanics, the failure modes of thesurrounding rock mass of the tunnels are discussed, and the reinforcing mechanism of thebolts and shotcrete is analyzed. The main results discussed in this thesis are as follows: (1) According to the loading characteristic of the surrounding rock mass of the tunnels,the growth and coalescence modes of the discontinuities are analyzed systematically, andthe dominance inclination angle of discontinuities in the rock mass is discussed. Thegrowing and coalescing characteristic of the compression-shear or tensile-shear mixed modein rock mass is studied, too. (2) Taking the tunnel of the circular cross section as the example, the loadingcharacteristic of micro-discontinuities and surface discontinuities surrounding the tunnelsand their fracture modes are analyzed. Based on the theory of fracture mechanics, theformulations of dimension and depth of the disturbed domain are obtained. The results showthat the dimension of disturbed domains is influenced by the cross section of tunnel, in-situstress, fracture toughness of rock, spaces between the discontinuities, length and shearingcapacity of the discontinuities. (3) By theoretical and numerical methods, the resisting function of the shotcerte to thestructural plane growth is studied. Further more, the failure mode and treatment methods of V<WP=6>the concrete supporting layer are analyzed by the fracture theory of plates. The results implythat the resisting effects of the shotcrete on the inner discontinuities are less influence thanthat on the surface planes. So, the main function of the shotcrete is used to resist the growthof surface planes. The variety of the shotcrete thickness has little influence on the resistingcapability of the discontinuities. However, the thicker the shotcrete is, the stronger to theexpanding stress of surrounding rock mass will be. The failure zone in the shotcrete can berestricted by bolts. The smaller the distance of the bolts is, the less of the failure zone willbe. (4) The growing modes of the surface discontinuities under compressive load and thefunction of the bolts are studied by the experimental methods. At the same time, thenumerical analysis is used to verify the results. The results demonstrate that there are somewing cracks and secondary cracks at the tip of the surface discontinuities. With the increaseof the inclination angle between the structural plane and the surface, the propagationbecomes more easily. The secondary cracks may be more popular for the case of the smallinclination angles. The role of bolts is to improve the performance of the structural mass,weaken the stress intensity at the c

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