【作者】 彭宁波；

【导师】 言志信；

【作者基本信息】 兰州大学 ， 地质工程， 2014， 博士

【摘要】 边坡失稳往往会导致巨大的人员伤亡和财产损失,尤其在地震中,这一灾害将更加严重,故而提高边坡抗震性能的加固技术研究在工程实践中具有重要意义。边坡加固工程中,锚固技术因施工方便、经济,扰动小,效果好等特点,得到了成功而广泛的应用,但对边坡锚杆的加强机理仍缺乏深入的认识,锚杆对边坡动力性能的影响研究尤为匮乏。现有的研究还不能很好的解释地震作用下锚固岩质边坡的破坏机理,还没有公认合理的方法来判断边坡的动力稳定性,地震作用下边坡锚杆的锚固机理研究还不深入。因此研究锚固边坡的抗震性能,进而实现边坡锚固的优化设计已成为工程实践中急需解决的问题。影响岩质边坡的稳定性的因素有很多,地震是最重要的外部影响因素之一,同一边坡在不同地震波的作用下其动力响应特征是不同的。岩质边坡的稳定性主要由岩体的结构控制,由于岩质边坡的结构形式多种多样,因此其破坏机理并不唯一。对于具有不同结构的岩质边坡,地震作用及锚杆的锚固作用也应该是不同的。锚杆的锚固作用主要应该是通过改善边坡岩体的结构特征,并体现在边坡的动力响应特征上。分析边坡的动力响应是研究边坡的破坏机理、动力稳定性以及锚固机理的重要研究手段。本文采用FLAC3D对一锚固顺层岩质边坡进行了数值模拟研究,通过对地震作用下锚固岩质边坡的位移、加速度、锚杆轴力等动力响应分析,发现锚杆轴力与其附近围岩的应变直接相关,并利用响应加速度傅立叶谱研究了锚固作用对边坡岩体宏观性能的影响。结果显示,边坡的相对位移时程曲线不能直接作为边坡是否破坏的判据,应进一步进行应变分析判断边坡是否破坏；锚杆能显著减小边坡的应变值,提高边坡岩体间的变形协调能力,增强边坡的抗震性能,岩体的应变越大,锚杆的锚固效果越好；边坡的永久位移是由较大地震加速度激发的,且在地震作用过程中存在累积效应；锚固作用能改善岩体的材料属性,但效果不明显。由于动荷载作用对边坡的名义剪应变和等效拉应变具有放大作用,故可根据“荷载激励法”来确定边坡破坏面的位置。通过输入不同的地震波,研究了波型以及振幅、频率及持时等地震动参数对同一顺层岩质边坡的地震动力响应的影响,得到了不同地震动参数对边坡动力响应的影响规律。虽然不同地震作用下,同一边坡的动力响应不同,但岩层交界面是动力响应特征的分界面,边坡的结构特征是边坡动力响应特性的主导因素,锚杆对岩质边坡的锚固作用主要是改变或改善了边坡的结构特征。因此,复杂的边坡地震动力稳定性问题可回归到边坡的结构特征上。为进一步探讨边坡锚杆在动载下的锚固作用与锚固机理,采用几种岩质边坡中常见的岩体结构元件破坏模型,探讨了地震力和锚固作用对不同岩体模型稳定性的影响。分析边坡锚杆系统在地震作用下力的传递过程,提出了一种单锚杆锚固体系的动力简化分析模型,并对模型的合理性进行了验证。利用提出的动力简化模型,基于锚杆荷载分布解析解对含有单结构面和二结构面的岩体模型进行了锚杆荷载分布的求解,讨论了岩体、锚杆的材料参数以及不同地震作用状态对锚杆荷载分布的影响,从受力分析的角度探讨了锚杆的锚固机理,并提出由多组结构面控制的岩质边坡的优化锚固方式。最后以石窟崖体作为工程案例进行分析。对于石窟崖体这种特殊的岩质边坡进行动力响应计算时,不可忽略其复杂的几何特征。为建立较为精细的石窟崖体3维模型,使用全站仪,利用激光测距的原理可获取石窟崖体表面的点云坐标,然后通过CAE软件进行辅助建模。基于边坡动力响应数值分析方法,对石窟崖体进行地震动力响应分析,得到了具有复杂几何特征的石窟崖体的动力响应特征,讨论了石窟的开凿对崖体动力响应的影响,并分析了地震作用下石窟的破坏模式及其原因。使用曾在石窟加固中使用过的小锚杆对模型上部岩体进行加固,并对锚固石窟模型进行动力计算,分析了锚固崖体的动力响应特征,探讨了小锚杆锚固的抗震性能并给出了工程建议。本文的研究有助于进一步认识锚固岩质边坡的地震动力响应规律,地震稳定性以及动力作用下边坡锚杆的锚固作用和锚固机理,为岩质边坡的锚固设计提供了一定的理论依据。更多还原

【Abstract】 Slope failure wherefrom heavy casualties and property loss can occur will be a greater calamity in the earthquakes, so that it is of great significance in engineering practice to study how to improve the seismic performance of the slope reinforcement technology. As we know, the anchorage technique has been successfully and widely used due to its convenience, economy, less disturbance, and efficiency. However, the current understanding of the slope anchor’s strengthening influence on the slope dynamic performance is still not thorough but deficient in research. The currently existing research still cannot abundantly account for the failure mechanism of rock slopes, and there is no method acknowledged to be a reasonable calculation of the seismic stability of rock slopes. Moreover, the anchoring mechanism researches of the bolts in the rock slope under earthquakes are lack of in-depth. Therefore, in engineering practice, it is urgent to study on the seismic performance of anchored rock slope, whereby the slope anchorage can be optimized.There are many factors affecting the stability of rock slope, and earthquake is one of the important external factors. Since the stability of rock slope is mainly controlled by rock mass structure, failure mechanism of rock slope varies with the structures. For the slopes of same structures but under different seismic waves, the seismic responses characteristics are different; And for rock slope of different structures, the effects of earthquake and the anchor effects of anchored rock slope also should be different. So the anchor effects should be improved by optimizing the structure characteristics of slope rock mass and the effects will be reflected on the dynamic responses characteristics of the slopes.Analysis of the slope seismic responses is an important means to research the slope failure mechanism, seismic stability and anchoring mechanism. In this paper, we established an anchored rock slope model and computed it using the finite difference software FLAC3D. The seismic responses, such as displacements, accelerations, axial forces of rock bolt, are analyzed so that the interaction between rock bolts and the surrounding rocks and the influences of the anchor on rock mass material properties are presented and discussed. The results show that the permanent displacement is excited by larger accelerations, and the increase of displacement is a cumulative process. Anchor can also improve the material properties of rock mass, but the effect is not obvious. We also give a failure criterion of rock slopes under the earthquakes based on the average tension strain and nominal shear strain suggested in this paper. Especially, the criterion only needs the data of displacements on the surface of slope which are easily obtained in engineering monitoring. Additional, a method to determine the failure surface is put forward base on the seismic simulation.In order to study the influences of different ground motion parameters, including amplitude, frequency and duration of earthquake, on the seismic responses of rock slopes, we applied different waves to the model, and then got the law of influences. The results showed that the structure characteristics are the dominating factor of the dynamic responses, and the main function of anchor is to improve the structure of slope in the aspect of anti-seismic. Hence, a complex analysis of the seismic stability of slope can be reduced to an analysis of the slope structure.To further explore the anchor role and mechanism of slope bolts under earthquakes, we adopted different damage models of rock mass structure components and discussed the influences of seismic force and anchor force on the rock mass stability. Then the transfer process of the force in the slope bolt system is analyzed, and a simplified dynamic model of single anchored rock system was presented. Based on the simplified model and the analytical solutions of the bolt axial force distribution, the distributions of bolt in the anchored rock model including single and double interfaces were calculated. Then the influences of different stress status in the process of earthquake, the rock mass and bolt material parameters on distribution of axial force were discussed. In addition, we also presented an anchoring mechanism of slope bolts from a perspective of force analysis, and put forward with an optimal anchoring design of rock slope which is controlled by multiple structural surfaces.The final part of this paper unfolds based on the analysis of Grottoes cliff. For such a special rock slope of the complex geometric features, the geometric characters cannot be ignored to simulate its seismic responses. We obtained the coordinates of points cloud on cliff surface using total station, and then built a relatively fine3D model with the CAE software. Based on the method of seismic responses of slope analysis, we simulated the seismic responses of grottoes cliff, obtained the dynamic responses characters of grottoes cliff, discussed the influences of digging grottoes on dynamic responses of cliff, and analyzed the possible failure modes and the causes, In addition, we simulated the seismic responses of anchored cliff by reinforcing the upper rock mass of the model with small bolts which was used in the grottoes reinforcement. Then the seismic performance of small bolts was discussed, and the suggestion of anchoring engineering was given.The results of this paper contribute to further understanding the seismic responses, seismic stability of anchored rock slope, and the anchor role and anchoring mechanism under the earthquakes. These also provide some theoretical basis for anchor design of rock slope.更多还原