【作者】 董建华；

【导师】 朱彦鹏；

【作者基本信息】 兰州理工大学 ， 结构工程， 2008， 博士

【摘要】 我国西北地区大多为黄土山区,在高等级公路、铁路的修建和城市的建设都需要对边坡进行支挡。而我国又是地震高发区,地质条件复杂,很多公路和铁路不可避免地穿越高烈度地震带。所以,研究在地震作用下土钉支护边坡的动力分析及抗震设计方法是很有必要的。更何况,土钉支护边坡与纯土质边坡又有所不同,它不仅存在土体和土钉锚固体的相互作用和协同工作,还存在挡土结构与土体的相互作用和协同工作,所以其振动特性比纯土质边坡复杂得多。本文对土钉支护边坡动力分析及抗震设计计算方法进行了研究,提出了新的思路及计算方法。(1)在动力荷载下,土体和结构是一个受力的整体,变形和运动相互制约,无论是土体还是结构的性质都将影响土与结构系统的动力响应。因此同时考虑了土体与结构的性质以及它们之间的相互影响和协同工作,建立了土与土钉支护结构系统动力计算模型,这种模型将土体对土钉的作用处理成一个线性弹簧和一个与速度有关的阻尼器,把面板对土钉的惯性作用简化为集中于土钉头上的等效质量加以考虑,以此为基础,建立土钉土体系统地震动力作用下的阻尼微分方程,求解了在简谐地震作用下土钉动力响应的解析解。最后,结合一案例进行分析,并用大型非线性有限元软件ADINA对此计算模型进行验证。结果表明该计算模型可以比较准确地反映土钉的实际受力,实现了土钉、面板和土体的协同工作计算,保证支护结构的安全可靠。(2)参照上部结构抗震设计的方法,对土钉支护边坡的抗震设计提出了三个水准的抗震设防要求和两阶段设计法。综合考虑输入地震波的特性、边坡土体特性、坡高因素,以及土体边坡在水平地震激励下,其位移响应主要为剪切型变形,建立了土钉支护边坡地震动力简化模型。该模型将同一水平层不稳定土体、稳定土体在水平地震作用下运动趋势假想为同步,两者之间相互作用很小,因此取不稳定土体和面板为研究对象。由于面板很柔,其运动随着土体的运动而变化,其刚度只考虑剪切刚度,将土钉处理成弹性支座,建立了土钉支护边坡振动方程,求解了在简谐地震作用下土钉支护边坡动力响应的解析解,通过该模型可以得到滑移面附近土钉轴力动力响应和土钉支护边坡的弹性动位移响应,也可以得到地震响应沿竖向的变化。对传统基于刚性挡墙的土压力求解进行了改进,而传统的土压力只能计算主动和被动这两种极限破坏状态下地震土压力的合力,不能准确地评价地震土压力的分布,没有考虑墙体的变形、设计参数以及破裂面的影响。根据破坏模式及极限平衡理论,推导了面板的冲切和钉头粘结承载力验算公式。最后,结合案例进行了分析,比较了按此分析方法与用ADINA按弹性有限元方法计算的结果,两者吻合较好。故这种方法可用于土钉支护边坡的第一阶段的抗震分析与设计。(3)在考虑土钉支护作用的情况下,根据土质边坡的破坏模式,基于极限平衡理论和拟静力法建立了土钉支护边坡地震稳定性分析模型。对边坡作用水平加速度时采用竖向条分的不合理性,提出了水平条分和竖向条分联合的方法进行改进。推导了基于计算机搜索法的边坡土钉支护滑移面动态搜索模式,实现了随着土钉墙设计参数变化的土钉支护稳定性动态分析过程。经计算表明,土钉墙设计参数的变化与土钉墙最危险滑移面之间是一个动态的变化过程,基于滑移面动态搜索模型进行土钉支护动力稳定性分析,较好地解决了通常由经验指定最危险滑移面,或者未考虑土钉作用进行稳定性分析存在的不合理性。利用遗传算法对最危险滑移面的圆心进行动态搜索,并且避免了在圆弧搜索中陷入局部最小值的缺点。最后,编制了土钉支护边坡动力稳定性分析程序。(4)基于稳定性分析模型,建立了地震作用下土钉支护边坡永久位移计算模型。提出了永久位移由地震作用过程中位移和震后位移两部分组成。在求解平均加速度时,通过第3章的弹性动力计算模型对Newmark有限滑动位移法的刚性假定进行改进。采用遗传算法动态寻优实现边坡地震过程中永久位移计算。运用功能原理建立地震作用后永久位移计算模型并求解。根据土钉柔性结构特性,对土钉震后随土体滑移机理提出褶皱台阶变形来计算土钉的滑移摩阻做功。给出基于边坡永久位移控制的土钉支护结构动态设计理念及程序步骤,并用实例进行计算及数值验证,结果表明震后位移量与地震作用过程中位移的比值很大,因此震后位移不能忽略。(5)采用大型非线性有限元软件ADINA对土钉支护边坡进行动力响应分析。考虑土体和支护结构相互作用及其协同工作建立三维有限元模型,应用非线性静动力性能的弹塑性模型模拟土体;采用可以描述土钉在进入塑性阶段强化性质的双线形弹塑性模型模拟土钉;土与支护结构相互作用由接触单元模拟。对一土钉支护边坡在输入不同的地震波,不同的加速度峰值,不同的支护工况下的动力响应进行了计算、对比、分析,得出了各种工况参数对边坡地震响应的影响和一些有益结论。更多还原

【Abstract】 There are a number of mountains and valleys in the west of China, therefore flat lands are extended to provide platforms for buildings, roads and other infrastructures when these facilities are constructed in this region. This frequently requires cutting of slopes and filling of valleys. In order to ensure that these facilities work in the right way it is essential for us to adopt retaining wall to prevent landslides and debris flow from occurring. Our country is an earthquake region and the geological condition is complicated. Thus, a lot of the highways and railways will pass through the region of high earthquake intensity. So, it is necessary to study the characteristics of the slope protected by soil nailing under the earthquake. Moreover, the slope protected by soil nailing is different to the pure soil slope. Not only the interaction and work together of surrounding soil and soil nailing but also the interaction of the soil and the facing are considered in the systems. So its characteristic of vibration is much more complicated than the pure soil slope. The comprehensive theoretical analysis and the numerical simulation have been carried out for the soil nailing flexible supporting structure under earthquake. The main work and conclusions gained are listed as follows:(1) A dynamic calculation model of soil nailing protected structures for the slope is proposed. The interaction between soil and soil nailing is treated with linear spring and damped system related with velocity. The influence of the facing upon soil nailing is simplified for equivalent mass. Under the condition of horizontal earthquake excitation equation of vibration response is established in according with being mentioned ahead, the analytical solutions are obtained for steady vibration. The method is applied to a case record for illustration of its capability, in order to verify the method 3-D nonlinear FEM (ADINA) is used to analyze the seismic performance of this case, the comparative results show that the design and the analysis are safe and credible using the proposal method. The calculation model provides a new approach for earthquake analysis and antiseismic design of slope protected by soil nailing.(2) Corresponding to design method of tall-building seismic design, the request of three levels seismic design and the design way of two stages are proposed for the slope protected by soil nailing. Considering seismic excitation property, soil property and slope height, occurring shear displacement under horizontal excitation, a simplified dynamic calculation model of soil nailing protected structures for the slope is proposed. Based upon the hypothesis which the lateral displacement of the stability soil and instability soil is nearly in phase and the lateral interaction between them is ignored under horizontal excitation, the instability soil and facing is treated as study object. Because the facing is flexible, its lateral displacement depends on the lateral displacement of instability soil. The soil nailing is served as the elastic supports. Under the condition of horizontal earthquake excitation equation of vibration response is established in according with being mentioned ahead, the analytical solutions are obtained for simple harmonic vibration. The soil nailing axial force response near failure surface, elastic lateral displacement time history and vertical seismic response distribution can be obtained by this method. The method and 3-D nonlinear FEM (ADINA) are applied to a case record for illustration of its capability, the comparison of results, using the proposed approach and FEM shows good agreement. This method can be used the first stage seismic design and analysis for the slope protected by soil nailing.(3) Under the situation of considering the soil nailing effects on stability of soil side-slope, according to the damage model of the slip surface, the limit equilibrium theory and pseudo static approach, the seismic stability model is set up. Errors should be induced in calculating horizontal seismic inertial force and anti-sliding moment according to vertical slice. The seismic stability analysis method of slope protected by soil sailing is improved by using horizontal and vertical slice method. A dynamical search model is set up for the critical slip surface determination of soil nailing wall, and the dynamical stability analysis of soil nailing wall is realized. By calculating, it is showed that the location of critical slip surface is varied with the design parameters of soil nailing wall. Soil nails have great effect on the slope stability. Compared with the experience methods, it is a good method for the stability analysis of soil nailing wall based on the dynamical search model of slip surface, and can overcome the irrationality without considering the effect of soil nails. Calculation of the stability of slip surface is carried out by using the genetic algorithms. It can avoid getting in local minimum in optimal design. Finally, using object-oriented programming language VC++, a computing program is implemented to make the optimization course reality.(4) Based on the analysis model of seismic stability, the permanent displacement calculation model of slope protected by soil nailing is established under earthquake. The total permanent displacement consisted of two parts of the earthquake displacement and the post-earthquake displacement is proposed. The solution of average acceleration adopts the elastic dynamic calculating model of Chapter 3 to improve the rigidity assumptions of Newmark method. Using genetic algorithms to search yield acceleration can achieve the permanent displacement of slope under earthquake. Using principle of works and energy, the calculating model of post-earthquake permanent displacement is established and solved. According to soil nailing characteristic which is flexible, after the earthquake the "folding steps" slip deformation mechanism is proposed to calculate the sliding friction works of soil nailing. The dynamic design philosophy and procedural steps of the soil nailing structure are given based on the control of the permanent displacement of the slope. The analysis results show that the ratio of post-earthquake displacement and seismic displacement is great, post-earthquake displacement can not be ignored.(5) Combined with the reality highway slope protected by soil nailing project, nonlinear FEM (ADINA) is used to analyze the seismic performance of slope protected by soil nailing retaining wall. On the base of works together and interaction between loess and flexible retaining wall, 3-D nonlinear FEM model is formed. A model that is capable of simulating the nonlinear static and dynamic elastic-plastic behavior of soil is used to model the soil, and a bilinear elastic-plastic model that has hardening behavior is used to model the soil nailing. Friction-element is employed to describe the soil-structure interaction behavior. By calculating, comparing and parametric analysis, some useful conclusions is drawn, these conclusions can be for reference in constructing some similar engineering and the design.更多还原