【作者】 徐光兴；

【导师】 姚令侃；

【作者基本信息】 西南交通大学 ， 道路与铁道工程， 2011， 博士

【摘要】 作为岩土工程和地球环境工程中的重要课题之一,地震作用下边坡的稳定性问题事实上涉及两个层面,即具体边坡工程的地震稳定性分析和区域性的边坡地震稳定性评估,每个层面的研究都有许多问题需要突破。特殊的地理地质条件和地震构造活动决定了边坡地震稳定性问题在我国特别突出,当前,我国的公路、铁路、水利等基础设施建设正处于高速发展期,这就对具体边坡工程的抗震设计和区域性滑坡风险评价提出了更高的要求,现有的理论和实践尚不能很好地满足这一需求；汶川地震在造成大量崩塌、滑坡等同震地质灾害的同时,也极大地改变了震区的山地灾害成灾环境,使得龙门山地区原本脆弱的地质环境变得更为恶劣,因此,震后次生山地灾害成灾环境演变程度的评估已经成为灾后重建所面临的亟待解决的关键科学问题。围绕国家基本建设和汶川地震灾区规划重建的国家需求,基于汶川地震边坡震害调查、大型振动台模型试验、数值模拟和理论分析等技术手段,论文较为系统地研究了地震作用下边坡的动力特性和动力响应规律、永久位移的分析计算、基于位移控制的抗震设计方法、区域性边坡永久位移的预测以及汶川震区山地灾害成灾环境演化规律等科学问题,涉及到边坡地震稳定性分析微观和宏观两个层面的若干问题。主要工作及研究结论如下：了解地震作用下边坡的动力响应规律及其影响因素有助于揭示边坡的动力失稳机制,进而指导抗震设计。利用单面坡和自由场,单面坡、凹形坡和凸形坡两组振动台模型对比试验,结合数值分析,研究了地震作用下边坡的加速度和动土压力响应规律,以及地震动参数、边坡形态对动力响应的影响。结果表明,边坡对输入地震波存在垂直放大和临空面放大作用；随着输入地震动幅值的增加,坡面加速度峰值放大系数呈现明显的递减趋势,表现出“量级饱和”特性；单面坡、凹形坡、凸形坡的振动台模型对比试验表明,就加速度动力响应而言,边坡坡形中总体上以单面坡最为有利,凹坡存在变坡点以上加速度急剧放大效应；边坡的永久位移随输入地震波振幅、持时的增加显著增大,随输入地震波卓越频率的增大而减小；输入地震波经过模型土介质传播后,其频谱特性会发生明显的改变,边坡土体对输入波的低频部分存在放大作用,对高频部分存在滤波作用,在模型自振频率附近,其频谱成分的变化幅度较之其它频段显著增加。边坡的动力特性是边坡体的固有动力学特性,深入研究地震作用下边坡动力特性的变化规律,有助于我们从坡体内在因素的角度认识边坡动力损伤过程,了解其动力破坏失稳的机制。介绍了传统的模态分析和传递函数理论,探讨了边坡动力特性参数的识别技术,建议利用绝对传递函数的虚部进行动力特性参数的识别。利用单面坡和加筋土单面坡两组振动台模型对比试验,研究了边坡动力特性的变化规律及其影响因素。随着振次的增加,模型边坡的自振频率逐渐降低,阻尼比逐渐增大。随着输入地震动幅值的加大,模型边坡自振频率降幅显著增加,阻尼比增幅也有随振幅加大而增加的趋势。当边坡的自振频率与输入地震波卓越频率相近时,自振频率的降幅增大。加筋土边坡模型的动力特性变化规律及其影响因素与纯土质边坡类似,但加筋可显著提高模型边坡的自振频率,使其远离地震波的卓越频率,从而减小地震作用效应。在相同的加载制度作用后,加筋土边坡模型的自振频率降幅远小于土质边坡模型。汶川震区边坡支护结构的震害调查发现,预应力锚索加固边坡表现出优良的抗震性能,为研究其抗震机理以便指导工程设计,开展了锚杆加固边坡的振动台模型试验。结果表明,地震作用下,锚杆加固模型的加速度放大系数明显小于不加锚杆模型,尤其在中震和大震情况下更为显著；大震工况下,边坡越高,锚杆加固对边坡加速度放大效应的抑制作用越明显：设置锚杆后整个坡体的自振频率有所提高,能对地震激励的共振有所避开,有利于减小地震作用效应；在相同加载制度作用下,锚杆加固边坡模型的自振频率降幅远小于土质边坡模型；随着输入地震波幅值的增加,锚杆轴力显著增加,并且幅值越大,轴力增幅越大,输入地震波的频率对锚杆受力影响不大,地震波的类型对锚杆的受力影响明显。随着对边坡动力稳定问题研究的深入,用单一抗震安全系数评价动力稳定性的不足已经得到普遍的认识。边坡的永久位移量化了边坡的受损程度,为坡体稳定性判识提供了一种可靠的依据。利用能量守恒原理,分析了地震作用下边坡的能量反应过程,提出了一种基于能量原理的边坡永久位移计算方法。研究发现,当滑动面倾角较小,且地震加速度较大或坡体自身稳定性较差时,反向位移不容忽略,否则算得的永久位移偏于保守；不考虑竖向加速度的临界加速度为一常数acd,考虑竖向加速度后成为一个随时间变化的临界加速度时程acd(t),利用acd代替acd(t)计算永久位移可能产生较大的误差；地震对滑坡主要产生触发作用,而由重力势能降主导边坡发生的永久位移量；设置支护措施后,可显著提高边坡的正向临界加速度,亦即提高边坡的抗震性能。基于位移控制的边坡工程抗震设计方法可提高抗震加固措施设计的经济性,较之拟静力法更为科学。通过锚索加固边坡永久位移的分析,探讨了基于位移控制的边坡工程抗震设计方法。国家基本建设中对待规模大、分布广的地震滑坡灾害问题,行之有效的方法就是在土地利用的规划阶段就考虑地震滑坡这一灾害问题。位移预测模型可以方便地用作区域性地震滑坡风险评价和震后滑坡灾势评估。利用汶川地震强震动记录,提出了适用于四川及其邻近省份等西部山区的边坡永久位移预测模型。发现基于强震动记录回归得到的永久位移测模型具有区域相关性,有必要在积累我国强震动记录资料的基础上,建立适用于各区域的位移预测模型。虽然Arias强度从物理意义上较PGA更能反映地震动特性,但计算复杂,并且以其作为回归参数的模型预测精度未见提高,建议采用以临界加速度比为参数的位移预测模型。汶川地震极大地改变了震区的山地灾害成灾环境,使得龙门山地区原本脆弱的地质环境变得更为恶劣,在地震发生后相当长一段时间内崩塌、滑坡等山地灾害都可能非常活跃。基于位移预测模型的理论框架,建立了强震区坡体损伤位移计算模型,定义了临界残余强度位移量和临界破坏位移量,作为衡量坡体损伤严重程度的判据。建立了基于地震坡体位移原理的一种山地灾害成灾环境演变分类体系：Ⅷ度及以下烈度的Ⅰ类区域为次生山地灾害环境轻度损伤区,地震发生时局部地区发生崩塌滑坡,震后以浅表层次生山地灾害为主,地质环境5年内基本可以恢复；地震烈度Ⅸ度及Ⅹ度弱的Ⅱ类区域为次生山地灾害环境严重损害区,地震时相当程度上诱发崩塌滑坡,震后次生山地灾害也会相当活跃,地质环境恢复期在5-10年左右；Ⅹ度强及以上烈度的Ⅲ类区域为次生灾害环境极度脆弱区,地震时大量触发崩塌滑坡,震后极易发生大规模次生灾害,地质环境恢复期在10年以上。Ⅹ度强及以上高烈度区山地灾害成灾环境已发生剧变,岩土体损伤严重,极易形成崩塌滑坡,是震后山地灾害防治的重点区域,灾后重建工作宜缓行。更多还原

【Abstract】 As one of important subjects in geotechnical engineering and earth environmental engineering, the problem of slope stability under earthquake actually involves two aspects, namely, the seismic stability analysis of specific slopes and seismic landslide hazard evaluation on regional slopes, and there are many issues need to be researched for each aspect. The problem of seismic slope stability in our country is particularly serious because of the special geological conditions and seismotectonic conditions. Currently, our country’s infrastructure construction such as highway, railway and water conservancy, etc. is in a period of rapid development, which puts forward higher request to anti-seismic design of specific slopes and landslide risk assessment of regional slopes, yet the existing theories and practice can not meet this requirement. Wenchuan earthquake not only caused numerous landslides, but also greatly changed the geological disasters environment, which made the fragile geological environment of Longmen Mountains even worse. Therefore, evaluating the degree of geological disasters environment evolution has become a key scientific problem need to be solved urgently in reconstruction after earthquake.To meet the national requirement of capital construction and post-disaster reconstruction in Wenchuan earthquake-stricken areas, several scientific problems, including dynamic response laws of slope, permanent displacement calculation, displacement-based anti-seismic design method, permanent displacement prediction for regional slopes and geological disasters environment evolution laws in Wenchun seismic area have been researched systematically in this dissertation, concerning issues related to slope stability analysis on micro and macro level. The research approaches include earthquake disaster investigations, large-scale shaking table model test, numerical simulation and theoretical analysis, etc. Major work and findings are as follow:Understanding of the dynamic response laws of slope under earthquake and their influencing factor is helpful to explore the seismic failure mechanism of slope, and thus to guide aseismatic design. Based on two groups of shaking table contrast tests on single-side slope and free field, single-side slope, concave slope and convex slope, combined with numerical simulation, the dynamic response laws of acceleration and earth pressure, as well as the influence of ground motion parameters and slope shape on the responses under earthquake were analyzed. Results show that the slope has vertical and surface amplification effect to input seism waves, the amplified coefficients of PGA along slope surface decrease with the increasing earthquake amplitudes, i.e. shows a characteristic of "magnitude saturation". Contrast test on slope shape shows that single-side slope is the best shape on acceleration dynamic response, and concave slope’s acceleration extremely increases above shape-changed point. The permanent displacement of slope evidently increases with the increasing earthquake amplitudes and duration while decrease with the increasing frequency. Input seismic waves’spectrum properties will be changed obviously after propagation through the model soil, the soil in slope has amplification effect to input seism waves at high frequency and filtering effect at low frequency, the changing amplitude has a significantly increase around the natural frequencies of the model slope compared to other frequency bands.As the inherent characteristics of slope, deeply understanding the dynamic characteristics’ variation laws and influencing factors under earthquake helps to understand the dynamic damage process and failure mechanism from the view of internal factors of slope. Based on the traditional modal analysis and transfer function theory, identification technique on slope dynamic characteristics was discussed, the imaginary part of absolute transfer function was suggested to utilize on identifying the dynamic properties of slope. Dynamic characteristics variation laws of slope and its influencing factors were researched base on two groups of shaking table contrast test between single-sided slope and reinforced slope. Results show that the natural frequencies of model slope decrease with the increasing vibration number, and the decrease range expands with the increasing earthquake amplitudes, while the damping ratios increase with their increasing, the reduce rate of natural frequencies increase when the predominant excitation frequencies of input seismic waves approach to the natural frequencies of the model slope. Dynamic characteristics variation laws of reinforced slope and their influencing factors are similar to pure soil slope, yet reinforced materials can remarkably enhance the natural frequency of the model slope, make it away from the predominant frequency of seismic wave, and consequently reduce the effects of earthquake. Meanwhile, the reduce rate of natural frequencies of reinforced slope is far less then that of soil slope after the same load law.Wenchuan earthquake damage investigation on slope reinforcement structure shows prestressed anchor cable reinforced slopes have excellent seismic performance. In order to reveal their aseismic mechanism thus to guide design, a shaking table model test of prestressed anchor cable reinforced slope was carried out. Results show that the acceleration amplification factor of reinforced slope model is obviously less than the model without anchor, especial on the moderate earthquake case and the strong earthquake case. The restraining effect on acceleration amplification by anchor cable reinforcement increases with the increasing height of slope under strong earthquake condition. Anchor cable increases the natural frequencies of slope, as a result to avoid meeting the resonance frequency, tends to reduce the seismic effect, and the reduce rate of natural frequencies of anchor cable reinforced slope is far less then that of soil slope after the same load law. The axial force of anchor cable increase with the increasing earthquake amplitudes, the frequency of seismic waves has less effect on the cable axial force, while the type of input seismic wave has remarkable effect on it.With the farther research on slope dynamic stability, the dynamic stability evaluation method using single seismic safety coefficient has been found insufficient. The permanent displacement can characterize the damage degree of slopes quantificationally, thus provides an effective criterion on slope stability evaluation. According to the principle of energy conservation, the energy response process during earthquake was analyzed; a permanent displacement calculation formula of the slope with energy method was presented. Result shows that the reverse displacement can not be neglected when the slope has a small angle of sliding surface and weak stability, while the earthquake is strong, otherwise the result may be rather conservative. The critical acceleration is a constant, acd, regardless of vertical acceleration, yet it will become an acceleration time history, acd(t), vary with time when take the vertical acceleration into account, and there may be a considerable difference on permanent displacement calculation with acd instead of acd(t). Earthquake plays an important role on triggering landslides, and the permanent displacement is mainly determined by gravitational potential energy. Reinforcement can significantly increases positive critical acceleration, i.e. improve the aseismatic performance of slope. An anti-seismic design method based on displacement controlling may improve the efficiency of aseismatic reinforcement, and it is more scientific compared to the pseudo-static method. With the illustration of anchor cable reinforced slope, the anti-seismic design method based on displacement controlling had been discussed.A more effective way to deal with large scale and wide distribution seismic landslides in state’s basic construction is to consider this problem during the construction sites selecting stage, displacement predictive models provide a convenient tool for regional seismic landsides risk and landsides disaster evaluation after earthquake. Based on a large number of strong-motion records from Wenchun earthquake, a regression model predict permanent displacement suiting to Sichun and adjacent provinces was put forward. Result shows that the models developed based on strong-motion records have zone dependence, and it is necessary to establish displacement predictive models for various regions by accumulating strong-motion record data. Despite the Arias strength can describe earthquake characteristics better than PGA in physical sense, it is complicated to calculate and the model in terms of Arias fails to improve prediction accuracy, the regression model in terms of PAG is recommended to adopt as displacement predictive model.Wenchuan earthquake dramatically changed the mountain disaster environment, made the weak geological environment of Longmen Mountains even worse. Mountain hazards such as fallings, landslides and other mountain hazards may be extremely active for quite a long period of time after earthquake. A displacement calculation model on slope damage was established, displacements of critical residual strength and critical failure were defined to judge the damage degree of slope. A classifying system for environment evolution of mountain disaster based on seismic permanent displacement was established, its main contents are as follow:Regions of class I where seismic intensity isⅧand below are the slightly damaged zone of secondary mountain disaster environment, there were fallings and landslides in partial region in earthquake, and shallow or surface secondary mountain disasters may occur mainly after earthquake, geological environment in these areas can be repaired basically in 5 years; Regions of classⅡwhere seismic intensity is IX and weak X are the severely damaged zone of secondary mountain disaster environment, there occurred many fallings and landslides in earthquake, and secondary mountain disasters may be active after earthquake, geological environment in these areas require 5-10 years to recover; Regions of class III where seismic intensity is strong X and above are extremely worse in secondary mountain disaster environment, there triggered quite a lot fallings and landslides in earthquake, large-scale secondary mountain disasters may be easily take place after earthquake, geological environment in these areas need 10 more years to recover. Regions class III are the key zones of mountain disasters preventing, in which rock and soil material has been damaged severely, secondary mountain disasters environment has been changed acutely, and the post-disaster reconstruction should be suspended in these regions.更多还原