【作者】 杨为民；

【导师】 李术才；

【作者基本信息】 山东大学 ， 工程力学， 2009， 博士

【摘要】 结构面是岩体工程区别于土木工程其他领域一个显著特征,它将岩石材料切割成不连续介质,使问题变得复杂。尤其是节理和裂隙等微小结构面,遍布于天然岩体中,在工程中最为常见。而这其中,又尤以断续节理最为普遍,岩体的失效破坏往往是由于赋存于其中的原生节理在荷载作用下产生新生裂纹,并且逐渐扩展、连通,使岩桥贯通造成的。因此,研究断续节理岩体的相关问题具有实际意义。锚杆作为广泛应用于岩体工程中的一种加固构件,其锚固效果是显著的,但其加固机理尚不十分明确,尤其锚杆对断续节理岩体的加固机理更是少有研究。本文以断续节理岩体和锚杆为研究对象,通过室内试验和理论分析手段,研究了锚杆对断续节理岩体的加固机理。首先,基于大尺寸的加锚断续节理岩体试件,开展了室内单轴压缩试验。选定节理长度、间距、连通率及倾角等四个断续节理几何参数作为变量,研究了锚杆对于不同裂隙分布形式的岩体的加固效果。对比分析了试件在加锚前后的裂纹扩展规律以及试件破坏模式的差异,研究了锚杆加固断续节理岩体的规律。基于层次分析方法,分别以裂隙岩体的峰值强度增量和弹性模量增量为目标函数,研究了断续节理几何参数对锚固效应的敏感性,得出了影响锚固效果的敏感因素顺序。分析了断续节理岩体在压缩荷载作用下,岩桥的受力状态,研究了其在不同应力水平下的贯通模式。根据不同的破坏模式,分别分析了在岩桥贯通前,断续节理岩体的剪切抗力。岩桥贯通后,原生节理与新生裂纹构成剪切滑动面,该滑动面可看做粗糙节理面,在考虑了节理的剪胀作用后,得出了此时岩体的残余剪切抗力表达式。当节理发生剪切错动变形时,穿过节理面的锚杆也会随之发生变形,进而锚杆杆体内产生内力,该内力反作用于节理,即对节理产生锚固作用。首先在考虑了锚杆在节理面附近发生的拉伸变形、剪切变形以及局部转动变形的基础上,研究了随节理变形而变化的锚杆锚固作用规律。当锚杆在节理面附近处于弹性状态时,根据试验结果,认为锚杆变形后的的形状为双曲余弦函数,推导得出了弯矩和轴力共同作用下,在锚杆某点达到弹性极限时,杆体内的剪切力和轴向力。当锚杆在节理面附近处于塑性状态时,锚杆在继续增大的轴向力作用下发生大变形。假设锚杆材料服从Tresca屈服准则,得出了锚杆失效时的杆体内的剪切力和轴向力。求剪力和轴力的合力,并将合力向节理的切向与法向分解,得出了考虑锚杆变形的加锚节理模型。将断续节理岩体的力学特性与锚杆对节理的加固机理相结合,并考虑到锚杆对岩桥的加固作用,得出了加锚断续节理岩体锚固模型。岩桥贯通前,岩石材料变形较小,此时假设锚杆与岩石变形协调,得到了加锚岩石的等效弹性模量,并假设此时穿过节理的锚杆处于弹性小变形阶段,建立了在此条件下加锚断续节理岩体的剪切抗力模型。岩桥贯通后,认为此时锚杆处于塑性大变形阶段,结合断续节理的几何特点,并考虑到锚杆对粗糙节理的加固作用,推导得出了此时锚杆对断续节理岩体的加固模型。将所建立的理论模型应用于Sarma法中,用于计算边坡的安全系数。在计算条块的抗滑力时,首先根据应力条件判断岩桥破坏形式,再根据岩桥贯通破坏形式计算岩桥出现拉剪复合破坏或剪切破坏时滑动面上的抗滑力,对于加锚工况还可以考虑锚杆的锚固效应。工程应用结果表明,考虑了断续节理岩体细观破坏及锚固效应的安全系数计算方法更贴近客观实际。更多还原

【Abstract】 Structure plane is a characteristic of rock engineering. The rock was cut to discontinuous medium by the structure planes and the situation was changed to be complicated. Joints and fissures prevalently exist in nature. When the joint cut the rock material in a non-persistent way, the rock becomes intermittent jointed rock mass, which is the commonest formation in rock engineering. The failure of intermittent jointed rock mass was usually caused by propagation of secondary crack and perforation of rock bridge. So, the study of this kind of rock mass is practically meaningful. Rock bolt is widely used and achieves great efficiency in practice. However, the anchoring mechanism was not very clear so far, especially to the intermittent jointed rock mass. Hence, in this thesis, the laboratory tests and theoretical analysis were adopted to study the reinforcement mechanism of rock bolt to intermittent jointed rock mass.Firstly, the uniaxial tests were performed based on bolted intermittent jointed rock mass sample in large scale. In Chapter 2, the joint length, spacing, persistence and dip angle were selected as variables to study the reinforcement effect of rock bolt to jointed rock mass. The differences of crack propagation and failure mode of rock mass between bolted case and unbolted case were comparatively analyzed. Based on the experimental phenomena and data, some primary reinforcement rules were drawn. Then, AHP method was chosen to study the sensitivity of joints geometry parameters to reinforcement effect. The sequences of sensitivity were obtained, regarding peak strength increment and deformation modulus increment as target function respectively.In Chapter 3, firstly, the stress state of rock bridge was studied when the rock mass were under two-dimension compression stress. The perforation mode of rock bridge was analyzed and summarized to two categories under different stress level. Then, the shear resistance of rock mass was obtained for each perforation mode. After rock bridge failure, the original joint and secondary crack form a clear shear plane, which could be regarded as a rough joint. Considering the dilation, the shear resistance of rock mass in this situation was derived.When shear deformation happened in joints, the rock bolts that run through the joints also deformed. The force mobilized in the bolts reacts to the joints and performs reinforcement effect. So, the deformation of rock bolts was an important respect to the reinforcement mechanism. In Chapter 4, the anchoring effect to joint was studied considering the bolt tensile deformation, shear deformation and rotation near joint face. In elastic domain, the evolution of the mobilized forces in the bolt as a function of the displacements is obtained with the help of a variation formula. The deformed shape of the bolt is described by a hyperbolic cosine function. The forces at the elastic limit are calculated by a plastic hinge formation criterion, established by taking into consideration the interaction of the bending moment and axial force. In plastic domain, it is assumed that the axial force mobilized in the bolt continues to increase. The displacements are calculated using an axial rigidity secant which progressively decreases as a function of the plastic lengthening of the bolt. At failure, the mobilized forces in the bolt flush with the joint and the shear force based on the Tresca criterion. The displacements are calculated by a large deformation formula assuming that the length delimited by the plastic hinges attains the material’s failure strain. With the orientation and the intensity of the mobilized resultant force in the bolt, one can determine the reinforced joint’s shear strength by dissociating the bolt cohesion and the confinement effect.In Chapter 5, the results obtained in Chapter 3 and Chapter 4 were combined. Considering the anchoring effect of bolt to rock bridge, the shear resistance of bolted intermittent jointed rock mass were derived. Before the perforation of rock bridge, the equivalent deformation modulus of bolted rock material was obtained assuming the deformation compatibility between bolt and rock. Moreover, the shear resistance of bolted rock mass was calculated in this case, combining the result of Chapter 4. After the perforation of rock bridge, the anchoring effect of bolt to joints was applied to the jointed rock mass based on the geometry characteristic of intermittent joints. Taking the reinforcement of bolt to rough joint into consideration, the anchoring effect of bolt to the rock mass was derived in this situation.The theoretical model was applied in the Sarma method and used to calculate the safty factor for the slope. Firstly, the failure mode of rock bridge was judged according to the stress state. The shear resistance of slice was calculated based on shear-tensile failure or shear failure mode of rock bridge. The reinforcement effect could be considered in anchoring case. The total resistance divided by the total driving force equaled to the safty factor. The engineering application showed that the method adopted in this thesis achieved good results.更多还原