【作者】 刘汉香；

【导师】 许强；

【作者基本信息】 成都理工大学 ， 岩土工程， 2011， 硕士

【摘要】 在我国多山、多地震的地质构造背景下,斜坡地震动响应问题突出。2008年的‘5.12’汶川Ms 8.0级地震在山区引发了数以万计的斜坡次生地质灾害,损失巨大。震后,多数学者集中于震源机制、灾害形成机理或灾害风险管理与评价方面的研究,对斜坡的动力响应特性研究甚少。震后调查表明,斜坡的动力变形破坏多见于硬质岩中,在谷坡坡顶和坡形转折带等特殊部位响应尤为强烈。沿发震断裂带分布的极震区,竖向地震动力特征表现明显。对有关斜坡动力响应特性的宏观上的定性认识在国内外并不少见。然而,由于缺乏充足的地震实测数据,加上影响因素错综复杂,实现斜坡动力响应规律的时空定量化统一,从而用于指导工程实践还言之尚早。随着全球逐渐进入地震活跃期,对这一问题的研究必将具有重大的理论和现实意义。本文以‘5.12’汶川地震为研究背景,旨在通过物理模拟试验手段在一定程度上探讨斜坡的地震动响应特性及其规律,其主要工作与成果如下:(1)以‘5·12’汶川地震灾区典型斜坡岩体结构为模拟特征,采用水平层状上硬下软和上软下硬两种岩性组合概念模型,设计并完成了1:100比尺的大型振动台试验。从最开始的相似关系设计和相似材料选取,到传感器的布置,再到输入波的选取和制定加载方案等一系列工作中,建立了一套适合水平层状软硬岩组合型斜坡的试验准备与试验过程设计思路。(2)通过在模型底部输入不同类型(按频谱特性不同分类)、激振方向和振动强度的激振波,观测记录软硬岩组合型斜坡模型的宏观变形破坏特征及与以上输入振动参数的关系。同时,对斜坡模型的失稳破坏机制分析表明,上硬下软组合模型以崩塌破坏为主,而上软下硬组合模型发生“拉-剪”式的滑坡破坏。(3)试验共完成了101个工况的加载,通过布置在坡内和坡表的大量加速度传感器采集到了6000多条加速度水平向和竖直向分量的时程波形数据,随后提取出了每个波形的绝对峰值(PGA)并计算出其相对于台面的放大系数。通过对这些数值的分析比较,获得了两模型的水平向和竖直向加速度动力响应规律,并采用“单因素法”分析了激振波类型、激振方向和振动强度对加速度响应规律的影响。分析结果很好地揭示了加速度沿高程的非线性放大效应,以及水平向与竖直向加速度动力响应特性的差异。结果同时表明,激振波频谱特性的不同导致了模型完全不同的动力响应规律;合成向激振相比单向激振使模型产生了更强的响应;在天然波作用下,随着振动强度的增加,模型在水平向和竖直向的响应强度均有所减弱。(4)最后,对加速度时程波形进行了傅里叶变换,再利用两种常见的傅里叶谱比值初步探讨了模型不同高程部位对振动波的传递特性。两种谱比值较准确地确定了模型的基频分布。另外,模型表面与台面上的水平向加速度谱比值在模型的上段很好地揭示了模型动力响应对着振动强度增加而出现的非线性特征。更多还原

【Abstract】 China is a mountainous and earthquake-prone country, and problems caused by seismic slope response are prominent. During the‘May 12’Wenchuan earthquake in 2008, tens of thousands of secondary geological hazards were triggered in a mountain area, causing great loss. After the earthquake, most researchers oriented their work on source mechanism, hazard formation mechanism, or hazard risk management and assessment, however, research on seismic slope response was limited. Post-earthquake survey indicates that, dynamic slope deformation and failure mostly occurred in hard rocks, with the pronounced response in the special parts of valley slopes like crest and the transition part between two slope angles. Macroscopically qualititive knowledge of seismic slope response has reached a basic agreement at home and abroad. Due to the limited earthquake recordings, however, in addition to the complicated influence factors, it is to early to get a systematic understanding of the seismic slope response laws from the time and space angles, let alone guide the engineering practice. With gradually entering into the seismically active period on a world scale, study on seismic slope response is bound to have great significance in theory and practice.On the background of‘May 12’Wenchuan earthquake, the present paper aims to explore the seismic slope response characteristics and laws to some extent by means of a physical model. The main work and results are as follows:(1) Simulating the typical rock structures of slopes in the Wenchuan earthquake region, two conception models with combinational structures of hard rock overlying soft rock and soft rock overlying hark rock were designed to perform the large scale shaking table test with a geometric scale of 1:100. Through a secquence of preparation work on determing similitude relations , sensor arrangement, input motions and a loading scheme, a set of design plan has been established applicable to the horizontal layered combinational slopes. (2) Throgh exicating models at the bottom with input waves of different types, vibrating directions and intensities, the macro deformation and failure characteristics of models havd been observed, meanwhile, the characteristics related with the input parameters have been analyzed. The failure mechanism shows that, the hard material overlying soft material model failed in a collapse, while the other one failed in a landslide with the‘tension-shear’mechanical process.(3) A total of 101 loading conditions had been completed in this test. Through large amounts of accelerometers in the interior and on the surface of each model slope, about 6000 time history recordings in horizontal and vertical components had been obtained. Afterwords, the absolute peak acceleration (PGA) and its amplification relative to shaking table soleplate were calculated for each recording. By comparing these values, the dynamic response laws of two model slopes in horizontal and vertical components were analyzed, and the effect of input parameters on the response laws were also explored by the single factor analysis method.Results show well the nonlinear amplification effect along increasing elevations, and the differences in responses between two componts were also reflected obviousely. Futhermore, input waves having different spectrum features caused different response laws; excitation in a combination direction generated stronger response than in a single direction; when excitated in real waves, the response intensity in two components tended to decrease.(4) Finally, Fourior transformations are conducted on accerleration recordings. Then two Fourior spectrum ratios are calculated to explore the transfer features of models at different elevations for waves. The two ratios well indicate the foundamental frequencies of two models. Moreover, the spectrum ratios of horizontal components of the surface to the table soleplate (input motion) confirm the nonlinear seismic response of models in their upper parts as the input motion is intensified.更多还原