【作者】 张黎明；

【导师】 王在泉；

【作者基本信息】 西安建筑科技大学 ， 岩土工程， 2009， 博士

【摘要】 随着我国水利水电建设、资源开发和铁路交通的发展,遇到了大量的岩体高边坡、地下隧洞等工程开挖问题,其工程设计、施工、运营、稳定性等都直接依赖于岩体的强度、变形及破坏等特性。地下工程开挖是一个复杂的加、卸荷过程,而卸荷条件下岩体的力学特性、变形特征、本构方程等都与加荷条件下有很大的差异,因此,应用现行加荷岩体力学理论和方法研究地下工程的围岩破坏机理是不完全正确的。本文采用与隧洞真实开挖路径相一致的试验与模拟方法,从宏观和细观角度研究加、卸荷条件下岩体的力学特性、变形及破坏机理,探讨卸荷条件下的围岩稳定性分析方法和岩爆发生机理,为认识与把握开挖卸荷条件下的岩体失稳破裂机理提供依据。论文主要取得以下研究成果:（1）通过系统的不同应力路径下的完整岩样加、卸荷试验,研究了不同卸荷速度下岩石的变形、破坏特征及强度参数变化规律。结果表明:加荷阶段轴向应变起主导作用,卸荷阶段环向应变起主导作用;卸围压过程中,弹性模量与围压呈非线性关系降低,泊松比与围压呈非线性关系增加;在相同的初始高围压下,轴向应变的回弹值和环向应变的突跳值会随着卸荷速度的提高而增加,而在相同的初始低围压下却表现出相反的规律;岩样破坏特征分为:主剪切、共轭剪切、劈裂加剪切三种,并且与卸荷初始的围压值与卸荷速度密切相关;卸荷条件下岩样粘聚力c是降低的,内摩擦角φ是提高的;基于试验认识,采用统计分析方法,建立了一个能够反映卸荷特征的岩石本构模型,模型结果和试验曲线吻合较好。（2）通过对含天然节理岩样加、卸荷试验研究,揭示了加、卸荷条件下含天然节理岩样的变形、破坏特征及强度参数变化规律。结果表明:含天然节理岩样加、卸荷条件下的破坏形式分为两种,穿切节理面破坏和沿节理面破坏,穿切节理面破坏岩样的变形及强度参数特点与完整岩样的变形及强度参数特点相同;对加荷而言,夹角小于40°的岩样为穿切节理面破坏,夹角大于40°的岩样为沿节理面破坏;对卸荷而言,夹角小于35°的岩样为沿节理面破坏,夹角大于35°的岩样破坏规律不明显;在相同的加、卸荷条件下,沿节理面破坏岩样的强度明显低于穿切节理面破坏岩样的强度;卸荷破坏中,沿节理面破坏岩样卸荷开始后轴向应变出现加速发展趋势,弹性模量降低,泊松比增加。（3）基于大量室内试验,利用离散元程序PFC^2D,通过FISH语言编程,实现了加、卸条件下完整岩样和含节理岩样破坏过程的细观数值模拟,研究了加、卸条件下岩样破坏过程中裂纹的产生、扩展与贯通过程。结果表明:完整岩样加、卸荷破坏过程分为4个阶段,分别为线弹性阶段、裂纹产生并扩展阶段、裂纹定向扩展阶段、裂纹沿剪切带贯通阶段;含节理岩样加、卸荷破坏过程分为3个阶段,分别为线弹性阶段、裂纹产生并沿节理方向扩展阶段、裂纹沿节理面贯通阶段;与完整岩样相比,在相同的应力路径下,含节理岩样破坏的计算时间缩短,峰值强度降低,峰值应变增大,说明节理岩体更容易发生破坏;与加荷相比,同种岩样的卸荷破坏计算时间更短,峰值强度更低,峰值应变减小,说明卸荷容易导致岩体发生突发性脆性破坏;（4）分别采用解析法和二分法改进的有限元强度折减法对考虑开挖卸荷的隧洞围岩稳定性进行分析,提出隧洞安全系数的概念。解析法基于卸荷岩石本构模型,推导了围岩软化区、硬化区、弹性区及衬砌内任一点的应力和位移解析公式;利用二分法改进的有限元强度折减法对不考虑开挖卸荷和考虑开挖卸荷的围岩稳定性分析计算,可以确定隧洞的破坏面和安全系数,评价隧洞的稳定性;不考虑开挖卸荷的安全系数比考虑开挖卸荷的安全系数要高,不考虑开挖卸荷的围岩稳定性分析在实际工程中是偏于不安全的。（5）采用卸荷三轴试验的方法来探讨岩爆问题,从定性与定量的角度对岩爆进行研究。基于卸荷试验应力-应变曲线,按能量守恒原理推导了两体系统的平衡方程,建立了两体系统动力失稳问题的折迭突变模型,给出了岩体动力失稳问题的一般方程,得到了系统失稳前后的变形突跳值和系统能量释放的一般表达式;探讨性地提出应力差强度比岩爆判据,结合有限元方法分析了不考虑开挖卸荷和考虑开挖卸荷的不同形状的隧洞岩爆级别,应力差强度比岩爆判据的岩爆级别比应力强度比岩爆判据的岩爆级别低一级,不考虑开挖卸荷的岩爆级别比考虑开挖卸荷的岩爆级别低一级,考虑开挖卸荷的有限元计算更能反映实际隧洞围岩的应力分布,更能揭示岩爆的烈度、深度及宽度。更多还原

【Abstract】 With the deyelopment of water conservancy and hydroelectric engineering,resource development and rail traffic,a lot of excavation engineering problems exist,such as steep rock slopes and underground tunnels.The design,construction,management,and stability of excavation engineering directly depend on the rock’s strength,deformation,and failure.Excavation of underground engineering is a complex loading and unloading process.And the mechanical characteristics,deformation behaviour and constitutive model are different under loading and unloading conditions.So,it is not correct to evaluate the failure mechanism of rock mass for the underground engineering by method of loading rock mass mechanics.In light of characteristics of underground engineering,the loading and unloading experiments were carried out in this thesis. Deformation and failure mechanism of rock under loading and unloading conditions were studied. The stability analysis method of surrounding rocks and the mechanism of rock burst under unloading condition were discussed.The main work can be summarized as follows:(1) The deformation features,mechanical parameters and failure characteristics at different unloading velocity were obtained based on the loading and unloading experimental results.It showed that the evolution of volumetric strain was determined by axial strain under loading condition.However,it was determined by lateral strain under unloading condition.Elastic modulus decreased and Poisson ratio increased during the unloading stage.The rebound value of axial strain increased,while the lateral strain jump decreased with the initial confining pressure increasing at the same unloading velocity.However,they decreased with unloading velocity increasing under the same initial high confining pressure.The failure modes of rock specimens can be classified into three types:primary shear failure,conjugate shear failure and splitting-shear failure,which are related with confining pressure and unloading velocity.The cohesion of rock decreased but the internal friction angle increased in the process of unloading.Based on the experimental results,a constitutive model was established by using statistical analysis method.The model agrees well with the experimental result.(2) The results of loading and unloading experiments showed the evolution of failure modes, deformation behaviors and mechanical parameters of natural jointed rock specimens.It showed that the failure modes of the specimens can be classified into two types,one is shearing-failure across the jointed plane,the other is sliding-failure along the jointed plane.Shearing-failure across the jointed plane occurred when the included angle is less than 40°,otherwise sliding-failure along the jointed plane occurred under loading condition.Sliding-failure along the jointed plane occurred when the included angle is less than 35°.otherwise the regulars of failure modes are not obvious under unloading condition.Peak strength and residual strength of shearing-failure along the jointed plane are obviously lower than those of shearing-failure across the jointed plane.Axial strains tended to develop accelerate and the strains at peak strength increased obviously in the beginning of unloading stage for the specimens with sliding-failure along the jointed plane.Elastic modulus decreased and Poisson ratio increased during the unloading stage.(3) Based on experimental results,the numerical simulations of failure process for intact specimens and jointed rock specimens under loading and unloading conditions by discrete element procedure PFC2D were performed.And the cracks generation,expansion and piercing process were studied. The failure processes of intact rock specimens under loading and unloading conditions can be divided into four phases,i.e.linear elastic phase,initiation and expansion phase of crack, expansion along the shear zone phase of crack,crack piercing along the shear zone phase.The failure processes of jointed specimens under loading and unloading conditions can be divided into three phases,i.e.linear elastic phase,initiation and expansion phase of cracks along joints and crack piercing along the joints phase.Compared with intact specimens,the length of time from loading to failure is shorter for jointed specimens in the same stress path,and peak strength is lower,peak strain increase.Those results show that jointed specimens is more easily failure than intact specimens. Compared with loading condition,the calculation of numerical experiments for unloading damage is shorter,the peak strength is lower,the peak strain decreases,partial crack shear zone caused by the tension cracks after rock specimens failure exists,which show that the.sudden brittle rock failure can be caused easily by unloading.(4) The concept of safety factor of tunnel is brought forward based on the strength reduction finite element method for elastic-plastic analysis individually.And the safety factor and the plastic zone are studied under the two conditions of considering and not considering the excavation unloading. Based on the constitutive model of unloading rock,elastic-plastic analysis was performed on the tunnel under the equal pressure.The formulas of stress and displacement of the above zones are established.Analysis on the stability of surrounding rocks were done by the strength reduction finite element method under loading and unloading conditions,which can determine the failure surface and the safety factor of tunnel,and evaluate the stability of tunnel.The safety factor not considering excavation unloading is bigger than that of considering excavation unloading.Stability analysis not considering unloading excavation is biased towards unsafe.(5) Rock burst was studied by using triaxial unloading tests from qualitative and quantitative aspects.The equilibrium equation was obtained based on the conservation of energy principle and the whole unloading stress-strain curve.A fold catastrophe model of rock dynamic destabilization is generalized by adopting a general form of material constitutive equation.The equations of deformation jump and energy release of the material are obtained.The stress difference-strength ratio method was put forward,and the rock burst intensity of the same size and different cave shape was calculated without considering the impact of excavation unloading and considering the impact of excavation unloading by the finite element method.Result shows that the grade of rock burst predicted by the stress difference-strength ratio method is lower than by stress-strength ratio method. The rock burst grade is lower one grade for not considering the excavation unloading.The finite element method simulation considering unloading excavation is better to reflect the actual stress distribution in the tunnel surrounding rock,and also reveals depth,width and intensity of rock burst exactly.更多还原