【作者】 伍国军；

【导师】 陈卫忠；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2009， 博士

【摘要】 地下工程中,由于岩体流变特性所带来的诸多问题给洞室开挖后的结构安全增加了风险。在锚固岩体中,锚杆(索)长期有效预应力是关系到锚固工程成败的关键之一。大量的实践证明,地下工程洞室开挖后围岩体的长期流变影响锚杆(索)锚固支护的不稳定甚至失效,从而导致整个锚固体系的失稳。目前,国内外对流变岩体工程的长期稳定性、岩体锚固的时效性特征等许多关键基础性问题的研究尚属起步阶段。本文结合大岗山水电站工程,对地下工程的非线性流变特性、锚固时效性及锚固承载可靠性开展深入细致的研究工作,取得的研究成果:1.流变岩体锚固机理研究基于荷载传递机理,建立了锚固微元体轴力的微分方程,推导了广义开尔文流变模型及幂函数经验流变模型的微元体锚杆轴力随时间和应力变化的关系式,并得到以下结论:当微元体受拉时,锚杆轴力随时间有不断增长的趋势;而当微元体受压时,锚杆轴力则随时间不断的减小;以锚杆轴应力与围岩体的蠕变应变相关为切入点,从解析推导和数值计算两种方法上证明了锚杆应力峰值位置和围岩体塑性区相重合的结论。2.岩体非线性蠕变损伤模型研究建立了岩体非线性蠕变损伤演化方程,并根据大岗山水电站花岗岩室内三轴蠕变试验和辉绿岩脉现场单轴蠕变试验的结果对本构方程进行了参数辨识。蠕变损伤模型反映了损伤随粘性应变的增大而稳定发展,随时间的增长而不断增加,且损伤还能反映随岩体流变的快速破坏过程。3.岩体锚固界面剪切流变试验及其本构模型研究通过锚固系统界面的室内常规剪切和剪切流变试验研究,得到以下结论:随时间的增长,剪应变逐渐增大,而沿剪切面方向剪应变逐渐降低;锚杆的预应力则表现出先期的快速衰减,然后慢慢回升,最后基本稳定在某个相对不变的水平;在此基础上提出并建立了法向软接触的指数接触形式和剪切面的非线性流变本构模型,该模型考虑了法向应力的影响因而能更合理的反映剪切流变的力学过程;通过编制程序计算分析,得到以下结论:无沦系统锚杆还是预应力锚杆,在经过围岩体塑性区的情况下,均在锚杆长度方向某个位置出现了应力峰值;对于预应力锚杆,当预应力增大时,锚杆轴向应力的峰值向洞口移动:而流变后的锚杆轴向应力峰值则向锚杆深处移动。4.地下工程锚固体时变可靠性研究提出了锚固时变可靠度的概念,并在改进蒙特卡罗法的基础上,率先采用能明显节省样本数量,并能产生任意大小维数的分层-拉丁超立方复合抽样方法,自行编制了基于MATLAB-ABAQUS联合实现的可靠度计算程序,并对锚杆的承载可靠性进行了计算分析和评价,提出锚固体失效概率随着围岩体流变时间的增长而逐渐增加,随着预应力变化幅度的提高失效概率迅速减小的规律。5.大岗山水电站地下厂房长期稳定性及锚固时变可靠性研究在前面的研究基础上,以大岗山水电站地下厂房锚固工程作为研究对象,建立了考虑岩体流变特性、锚固界面接触模型和锚固承载力可靠性分析的计算模型,通过编制程序计算得到以下研究成果:地下厂房洞壁有一定的拉应力产生,塑性区主要分布在靠近主厂房的断层和岩脉部位,主变室和尾调室之间没有贯通,但有逐渐贯通的趋势;对穿锚索的分布特征是:两头大,中间小,随着围岩体的流变,除索1左端锚固力略有下降外,其他锚索锚固力均呈现缓慢增长的趋势;锚索锚固的失效概率随着流变时间的增长逐渐增加,增幅逐渐减小,锚索体系失效概率在流变一年时对应的失效概率为0.0085,可靠指标为2.39,基本符合安全要求。长期看来,锚固失效概率会有极其微小的增加,但最终会趋于稳定。更多还原

【Abstract】 The failure of caverns due to creep behavior of rock mass is common in underground engineering. Bolt and pre-stressed bolt to prevent long-term creep deformation is a good measurement in practice. However, there is few achievements on time-dependent behaviour of rock mass and its reliability on anchoring in underground engineering. With the background of creep properties of undeground powerhouse in DAGANGSHAN hydropower station. The main achievements are conducted as follows:1. Anchorage mechanism in rheological rockA differential equation describing load transfer mechanism between bolt and rock mass is established. Variations of axial stress distribution with time in bolt are deduced by both General Kelvin model and an empirical power index creep model, it is concluded that axial force in bolt increases with developing of creep deformation when it is in tensile stress state while decreases when it is in compressive stress state. Through analyzing the relation between axial stress of bolt and creep strain of rock mass, we make a conclusion that the location of peak stress of anchorage are consistent with that of length of plastic zone.2. Nonlinear damage creep constitutive modelA nonlinear damage model for creep rock mass is established. The parameter identification of the creep model has been done based on experimental and field creep test results. In addition, the creep damage characteristics have been analyzed, which indicate that the damage is stablely developing with time and viscous strain increasing. Furthermore, the damage model can show the failure process from stable creep stage to accelerating stage.3. Experimental study on anchorage interfaces and constitutive modelThe shear and shear creep experiments about interface mechanics of anchorage system are carried out. The shear creep strain grows with time and shear stress increasing. On the basis of experiment, a constitutive model which have a softened pressure-overclosure relationship in normal direction and a continuous contact formulation in tangential direction is proposed. The model is more reasonable because of its consideration of nomal stress. Using this model, it can be concluded: there is a peak stress along bolt when bolt passes through plastic zone of surrounding rock mass. By considering creep effect of rock mass, the anchorage peak stress moves towards the boundary as prestress increases, and toward inside as creep of rock mass occurs.4. Time-dependent reliability analysis of anchorage in underground engineeringIn this paper, a method analyzing time-dependent reliability of anchorage is proposed. On the basis of improved monte-carlo method, a new named Stratified—Latin hypercubic sampling is introduced which is more precise and less time-consuming. By using MATLAB and ABAQUS code, a program calculating the anchorage reliability is developed. With the program, Load-bearing capacity of anchorage is studied. The results indicate that the failure probability of anchorage system varies with rheological properties and amplitude of anchorage prestress.5. Long-term stability and time-dependent reliability analysis of anchorage for DAGANGSHAN underground powerhouseBased on design of DAGANGSHAN underground powerhouse, a numerical model considering nonlinear creep characteristics of granite, constitutive model of anchorage interfaces and the reliability of anchorage load-bearing capacity is established. The achievements from the numerical work can be concluded as follows:The stress of opthread-prestressed strand cables is bigger at two ends and smaller at intermediate parts. The axial force of opthread-prestressed strand cables increases due to creep of rock mass. The performance of strand anchor system is reliable for the failure probability is 0.85% and reliability is 2.39 correspondingly. The powerhouse is safety in long-term even considering creep and variation of mechancial parameters.更多还原