Disaster chains initiated by the Wenchuan earthquake

The Wenchuan earthquake caused numerous landslides and avalanches, which initiated causal chains of geological and ecological disasters. Field investigations and field experiments were performed in the earthquake area in 2008 and 2009 to study the disaster chains. Four types of disaster chains have been identified and seven cases have been studied. In the disaster chains, each episode was caused by the previous episode, or the causal episode. In the first chain, landslide created a quake lake, which was followed by landslide dam failure flood and very intensive fluvial process. The last episode of the chain was loss of habitats and destruction of aquatic biocommunities. The Tangjiashan and Huoshigou landslides initiated such a type of disaster chain. The second chain consisted of landslide, drainage system burying, debris flows, and development of new drainage system and intensive fluvial process. The Wenjiagou landslide initiated such a type of disaster chain. The third chain consisted of avalanches, grain erosion (unusual erosion of bare rocks due to insolation and temperature change), slope debris flows, and flying stones. Many such disaster chain events occurred on the mountains by the Minjiang River section from Yingxiu to Wenchuan. The fourth chain has only two episodes: avalanches during the earthquake occurring on elevation between 100 and 800 m from the riverbed, and rock falls or new avalanches due to increased slope angle of high mountains (400–1,500 m from the riverbed). The Chediguan bridge was broken by such avalanches in July 2009, in which six were killed and more than 20 were injured. For all the disaster chains, the volume of mass movement in each episode was much less than the causal episode (previous episode). In other words, there was an attenuation along the causal chains. The attenuation factor is defined as the ratio of the volume of mass movement or affected area in one episode of a chain to the volume or affected area in the causal episode. The study concluded that the attenuation factor ranges from 0.02 to 0.3. Macroinvertebrates were used as indicator species to evaluate the ecological effect of the disaster chains. The number of species was greatly reduced by the causal chains, although the river section was not directly affected by landslides.     

Characteristics and remediation of a landslide complex triggered by the 2008 Wenchuan, China earthquake-case from Yingxiu near the earthquake epicenter

During the 2008 Wenchuan earthquake, the river valley from Yingxiu to Wenchuan experienced numerous landslides and became a prominent area of landslide complexes. The present large landslide complex near the earthquake epicenter consisted of Laohuzui slide 1, Laohuzui slide 2 and Douyaping slide. The scale, geology, morphology, sliding process, and failure mechanism of the landslide complex are analyzed by means of field investigation, aerial photograph and stereographic projection technique. Characteristics of these three slides including seismic response of slope, landslide debris, damage and potential failure are discussed: the convex slope and the upslope of fractured granitic rock at high altitude are highly prone to landsliding under earthquake; the high source altitude and long travel path determine grain sizes and the deposit angle of the slide debris; the landslide complex completely buries the G213 roadway and dams up the Minjiang River in these sections; after the earthquake, rainfall, aftershocks and river erosion may retrigger new failures, such as retrogressive slide of weathered fractured rock, colluvial landslide, debris flow, embankment failure and rockfall. The following are presented as suggested remedial measures to protect the roadway and stabilize the slope: the removing and trenching, protective concrete/rock blocks against erosion, retaining structure, rockfall stopping wall, rockfall restraining net, rock bolt, and the planting of vegetation.     

黄河中游岩土侵蚀问题及防治对策探讨

黄河中游出露地层岩性主要有古生界奥陶系碳酸盐岩、石炭系和二叠系碎屑岩;中生界三叠系砂泥岩、侏罗系砂泥岩和白垩系砂泥岩;新生界古近系砂泥岩、新近系(原为第三系)红土及第四系风积黄土和现代风积沙。第四系黄土厚度大,结构松散,遇水易解体,具湿陷性,是黄河中游粗泥砂的主要物源;第四系风积沙分布于黄河中游北部,亦是黄河中游粗泥砂的主要物源。岩土侵蚀类型有五:一是风力侵蚀—风沙侵蚀;二是降雨对谷坡面的面状冲刷—坡面侵蚀;三是地表径流对谷底的侧蚀—沟谷侵蚀;四是滑塌对谷坡坡体的破坏—重力侵蚀;五是潜蚀。并对不同侵蚀类型提出了不同的防治对策。     

强震触发崩塌滚石运动特征研究

高强度、长持时汶川地震诱发大量边坡滚石,滚石源于岩体结构面切割而成的块体或岩土质边坡中尺寸较大的孤石。以汶川地震未扰动现场滚石痕迹的判识、测量取样及分析,得出强震作用下块体(石)是以一定初始速度抛射而出的; 其坡面运动表现为滑动、滚动、跳跃与3种方式的组合。选取2个典型强震崩塌点为例进行研究,基本结论:(1)与重力作用下崩塌滚石运动特征是有显著区别的,地震触发滚石具有一定的平抛速度,初始速度除与地震烈度有关外,还与地形地貌有关,其中变坡点、凸起点、端部速度较大; (2)滚石三边(长、宽、高)比例越接近,其运距越远; 坡面相对1/2高度以上,运动方式表现为跳跃-滚动、跳跃-滑动为主,其下滚石则以滑动、滚动运动为主; (3)规模(质量)大的滚石多停留于第一着地点附近或边坡坡脚宽缓地带,滚石运动消能方式为摩擦或碰撞解体; 滚石平台阻滞率为54％,树(灌)木拦阻率为12％。通过反演,计算了非弹性碰撞法向恢复系数Rn与切向恢复系数Rt,其中裸露基岩Rn=0.2,Rt=0.6,一般覆盖层Rn=0.3,Rt=0.8。滚石在运动过程中的弹跳理论高度在0.2~1.3m之间,坡面相对高差与最远滚动距离之比约为1/2。     

软弱基座型滑坡震裂机理研究

罐滩滑坡是“5·12”地震诱发的典型反倾软弱基座滑坡,滑坡在地震过程中并末立即滑移,而是在震后余震和降雨共同作用下产生的.为研究滑坡中下部软基在地震过程中对滑坡稳定性的影响,本文以罐滩滑坡的地质结构为背景,建立了有无软弱基座2种结构斜坡的概化模型,通过数值计算揭示了斜坡在地震动力响应过程中的应力演化过程及其破裂的产生和...     

汶川地震中锚固岩质边坡的动力响应特征

岩质边坡的地震响应是当前岩土工程界所关注的重要问题之一。以紫坪铺工程进水口边坡为研究对象,以现场监测数据为基础,从时间和空间的角度综合分析了汶川地震前、后支护荷载和边坡位移的变化特征,并讨论了坡体形态、岩体结构以及支护荷载对地震力作用的协同影响。研究结果表明：受地震力作用影响,坡体变形和支护荷载发生突变,主要受主震影响;地震引起的支护荷载变化量在100 kN以内,未超出设计荷载的5%;边坡水平向产生的永久位移在12 mm范围内,岩体变形深度受结构面分布控制;边坡中部变形最大,沿水平方向具有明显的临空面放大效应,而沿高程方向,没有明显垂直放大效应。研究成果可加深对锚固岩体动力响应机制的认识,同时为以位移控制的边坡工程抗震设计提供参考。     

粒度与岩石流变相关性研究进展

粒度对岩石的粘度、应变率和流变机制及转换具有重要的影响。在相同条件下,粒度越大,粘度越高。在粒度灵敏性变形中,粒度的变化有时对岩石应变率的影响也是显著的。大部分天然岩石是由不同粒度的矿物颗粒组成,不同粒度的颗粒在变形中可能受不同的变形机制控制,包含粒度分布参数的复合流动律改进了人们对天然岩石流变性的认识。岩石的变形过程同时也是粒度的不断修正过程,粒度的演化具有稳态化的趋势。     

汶川地震灾区某工程开挖边坡变形三维稳定性分析

汶川地震灾区某边坡,因厂房建设需要,对其进行开挖改造。鉴于其稳定性对工厂正常运行有重要影响,本文在岩体质量分级和岩体结构模型概化的基础上,采用快速拉格朗日差分法FLAC3D模拟边坡开挖,分析了边坡在自然条件、暴雨条件以及地震条件下的应力场、位移场、剪应变增量及塑性区的分布和变化特征。研究结果表明:边坡开挖引起坡面局部应力集中,后缘易拉裂破坏;降雨时呈现部分区域安全储备较低;在地震作用下,边坡处于不稳定状态。     

汶川地震诱发罐滩滑坡形成机制初步分析

安县罐滩滑坡由汶川地震诱发形成,发育于存在软弱基座的反倾斜坡中,体积达468×104m3。罐滩滑坡由"5.12"汶川地震及当晚暴雨诱发形成,发生时间滞后地震8 h,是典型的地震后效型滑坡。滑坡位于龙门山前山断裂带上盘,自然斜坡走向与断裂带近平行,水平距离约400 m,前山断裂带的分支断裂从坡体下部通过,并形成底部泥岩和上部白云岩的分界线。调查和分析表明,下软上硬的坡体结构是滑坡产生的基础,强烈的地质构造活动背景是其产生的重要条件,强烈的地面震动和高强度暴雨是导致产生滑坡的根本因素。滑坡的形成机制和发展过程可以分为以下3个阶段:自然斜坡的压缩-倾倒变形、震后滑面贯通阶段、滑坡整体破坏阶段。滑坡体形成沿河长400 m,纵向长880 m,平面面积1.82×105m2的滑坡堆积体,堵塞雎水河形成罐滩堰塞湖。     

岩石单颗粒压缩破碎的数值模拟分析

岩石颗粒破碎是影响粒状材料剪切强度和变形的最主要因素, 岩石颗粒破碎并不是想象的那么难, 像花岗岩颗粒有时在很小的压应力作用下就可以破碎。岩石单颗粒破碎的物理试验结果常常很离散, 完成大量单颗粒破碎的物理试验费时费力不现实, 采用离散单元法(Discrete element method, DEM)PFC软件模拟单颗粒压缩破碎试验, 既能克服单颗粒破碎物理试验的缺陷, 又能解决单颗粒破碎物理试验工作量大的难题, 是研究单颗粒破碎的理想选择。基于DEM的软件PFC2D, 将粒径为0.075～0.1245mm的基本粒子捆绑成不同粒径的单颗粒, 模拟岩石单颗粒压缩破碎试验, 观察颗粒破碎演化过程, 统计单颗粒破碎强度。计算单颗粒压缩破碎后颗粒分布的分维, 验证单颗粒破碎强度的分形模型和单颗粒破碎强度的尺寸效应。文中引用玄武岩单颗粒破碎试验结果, 与单颗粒破碎的离散单元模拟结果进行比较, 验证单颗粒破碎强度的尺寸效应和修正的Weibull理论的离散单元模拟结果。     

The rainfall-induced Wulipo rockslide,China: a modified model for rockslide initiation

During the May 12, 2008 Wenchuan earthquake, rock masses in the earthquake region were shaken, and subsequently, a number of post-earthquake landslides and debris flows occurred, triggered by heavy rainstorms. This paper presents a study of the rainfall-induced mechanism that triggered the landslides. This study is based on pre- and post-landslide geomorphology and geological features identified from pre-landslide high-resolution satellite imagery and post-landslide aerial photographs of the Wulipo landslide. The remote sensing observations were verified by field investigations. The results indicate that the heavy storm that occurred in July 2013 was the main trigger for the landslide although existing tensions and weak rock interfaces were the main internal causes for reactivation of the landslide. The bedding in the rocks dips in the same direction as the topographic slope. A tensile trough developed at the scarp. Based on data from the Wulipo rockslide, a model is proposed for calculating the safety factor for rockslides that takes into account the hydrostatic pressure along the structural plane of the rockslide. The results show that the proposed method can effectively estimate the stability of a storm-induced rockslide in regions underlain by bedded rocks. Based on this estimate, it is concluded that the Wulipo rockslide is a reactivated old rockslide.     

沙漠公路风沙土路基风蚀破坏试验研究

以沙漠公路风沙土路基为研究对象,通过室内风蚀风洞试验研究路基的风蚀破坏规律,以及路基不同断面对风沙流运动的影响。以路基高度、路基边坡坡率和路基宽度作为路基断面主要设计参数,研究不同路基断面下风沙流扰动、增速、减速、恢复的过程,以及路基周围风速流场的变化特征,分析路基病害较未病害时路基周围流场的变化。试验结果表明：路基高度和边坡坡率对风沙流运动的影响较大。随路基高度增加,路基对风沙流流场扰动增强,迎风坡坡顶处吹蚀破坏和背风坡坡底处堆蚀破坏越显著,在确定的路基边坡坡率下,路基模型高度为250 mm较模型高度为60 mm时,迎风坡坡顶风速增加1.13倍,背风坡坡底风速减小2.53倍,建议沙漠公路路基高度宜小于2.5 m。进一步,在确定的路基高度下,比较不同的边坡坡率对路基沿程风速的影响,发现当路基边坡坡率为1:1.75时,路基沿程风速变化不明显,沙漠公路风沙土路基不宜被风蚀破坏。     

沟道型滑坡-碎屑流运动距离经验预测模型研究

沟道型滑坡-碎屑流具有隐蔽性强、危险性高、力学机理复杂的特点,研究其运动距离预测模型具有重要的理论意义和实践意义。本文基于遥感GIS技术,结合野外调查,获取了汶川地震触发的38个沟道型滑坡-碎屑流的基础数据。通过相关性分析确定沟道型滑坡-碎屑流最大水平运动距离L的影响因素从大到小依次是滑坡体积V、最大垂直运动距离H、滑源区高差Hs、沟道段坡度β。采用逐步回归方法建立了滑坡-碎屑流最大水平运动距离L的最优多元回归模型,检验结果表明模型具有较高精度。将最优多元回归模型与国际上应用较多的滑坡运动距离和泥石流运动距离预测模型进行对比,表明考虑滑坡体积、地形落差和沟道段坡度的运动距离预测指标体系,具有最高的拟合优度和较好的物理含义,可为沟谷山区滑坡-碎屑流危险性评价提供参考依据。     

5.12汶川大地震诱发大型崩滑灾害动力特征初探

5.12汶川大地震发生于地质环境条件异常脆弱的龙门山地区,加上地震震级高、释放能量大,持续时间长等特点,汶川地震不仅直接诱发了数以万计的崩滑地质灾害,且表现出非常独特的动力学特征。在对汶川地震灾区崩滑灾害进行大量调查的基础上,结合建构筑物和斜坡岩体在地震过程中的变形破坏特点,本文从地震动力学和斜坡变形破坏成因机理的角度,揭示了汶川地震诱发的大型崩滑灾害具有震裂溃屈、临空抛射和碎屑流化等独特的动力学特征,为强震诱发地质灾害成因机理研究提供了新的认识。     

Origin and orientation of microporosity in eclogites of different microstructure studied by ultrasound and microfabric analysis

This work contributes to the experimental investigations of the origin and 3-D orientation of micropores in low porosity crystalline rocks. The origin and spatial orientation of microporosity in two eclogites with different microstructures were studied by 1) quantitative and qualitative microstructural analysis of grains and grain boundaries, 2) measurement of lattice preferred orientation using the SEM-EBSD method and 3) experimental measurement of velocity of elastic P-waves in spherical samples in 132 directions under confining pressures up to 400 MPa. Results show good correlation between the elastic properties and the orientation of grain boundaries and cleavage planes in clinopyroxene. The magnitude and anisotropy of velocity change with pressure shows that microporosity in the fine-grained sample is relatively large and strongly preferentially oriented, whereas it is significantly lower and less preferentially oriented in the coarse-grained sample. Seeing that the lattice preferred orientation of clinopyroxene is similar in both samples we can deduce from velocity changes that the grain size of the rock forming minerals controls the amount of microporosity. Also, the orientation of microporosity depends mostly on preferred orientation of grain boundaries and somewhat less on the orientation of cleavage planes. Grain boundaries are therefore the most important contributors to the bulk microporosity in the studied rocks.     

刘家湾滑坡特征及成因机制探讨

刘家湾滑坡位于青川东河口红光乡刘家湾,为汶川地震触发的特大型岩质山体滑坡。野外调查结果表明,该滑坡堆积体与一般汶川地震滑坡运动堆积体迥异的是滑体在沿碳质板岩与白云岩划分带破坏溃滑后,滑源区又沿白云岩风化卸荷带触发了二次溃滑,形成二级堆积平台的形态且以不同岩性区分,在岩性划分带及风化卸荷带呈现出明显的动力破坏特性。通过对该滑坡堆积体进行岩体物理力学试验及波速测试研究表明,该滑坡由白云岩、碳质板岩及千枚岩组成的内硬外软岩质边坡具有明显的量化差异特性,强震条件下差异岩性组合边坡岩层接触面的动力突变效应耦合凸出地形是导致该边坡破坏的主要因素。近一步研究显示该滑坡运动可大致分山体震裂阶段、地质分界面应力突变阶段、高速溃滑阶段、碎屑流堆积阶段、二次溃滑堆积5个动力过程。     

震裂斜坡形成机理及变形破坏模式研究

震裂斜坡是强震作用下形成的一类分布范围广、震裂变形严重、潜在危害大的次生地质灾害,为了深入系统地分析其震裂机理及变形破坏机制模式,本文结合"5.12"汶川大地震造成的震裂斜坡及其破坏现象的详细调查,在对强震中的地震波效应深入分析的基础上,以双面斜坡为例,首先对震裂变形的力学机理进行了系统分析。认为强震中的体波效应将导致斜坡体处于量值和方向不断变化的拉-剪应力和反压应力的交替作用之下,其形成的拉-剪破裂效应和潜在的楔劈效应是斜坡震裂变形的重要力学因素之一。同时,面波效应将导致坡体表面处于鼓胀拉力和扭力的作用之下,是坡体表部整体震裂破碎甚至破坏的另一重要力学因素。二者共同作用均使坡体应力场处于不断的动态变化过程中,坡体(面)震裂变形甚至破坏更为严重。在此基础上,对强震中斜坡变形破坏的机制模式进行了归纳,认为主要有四种表现形式,即旋转-拉裂型、旋转-剪滑型、鼓胀-拉裂型和滑移-拉裂型。研究成果为震裂斜坡稳定性分析以及灾后重建和防灾减灾提供了有力参考。     

震裂边坡稳定性极限分析

地震导致山体大范围开裂松动,使岩体裂缝（隙）张开、扩展进而形成危险的震裂边坡。裂缝是控制震裂边坡变形破坏的切割边界和滑移边界,为此,考虑裂缝扩展、裂缝充水和地震影响,采用极限分析上限法对汶川地震震中附近的一实地震裂边坡的稳定性变化进行分析。计算结果揭示了随裂缝扩展延伸,在雨水、地震作用影响下震裂边坡稳定性变化规律,为类似边坡的分析评价与工程治理提供了理论依据。     

地震诱发滑坡复活机制的FLAC~(3D)数值模拟分析

地震是影响斜(边)坡、滑坡稳定性的主要因素之一。白龙江上某大型滑坡经顺层斜坡发生倾倒变形而成,天然状态下处于基本稳定状态,在"5.12″汶川地震作用下,该滑坡有整体复活迹象,其后缘周界形成了连续贯通的拉裂缝、错动台阶,尤其是滑坡下游区变形拉裂较明显。本文以该滑坡在地震作用下发生复活为例,在分析滑坡所处的区域地质条件的基础上,详细研究了滑坡的基本特征以及地震作用导致滑坡复活的现象、特征,然后利用FLAC3D软件内置动力分析模块对该滑坡复活机制进行了分析、研究。数值分析表明,地震作用下滑坡变形破坏受坡体形态的影响较显著,滑坡对地震波具有明显的放大效应;同一地震动条件下,滑坡体相对周边处于稳定状态基岩边坡对地震更为敏感。这较好地解释了"5.12″汶川地震作用下,该滑坡的复活原因。     

冰缘地区岩质斜坡冻融侵蚀时空分异特征与产屑率研究

新疆天山地区是我国高海拔、高纬度、大温差典型代表冰缘山区,本文基于气象水文站及现场监测获取的大气温度和降水变化规律,建立了天山地区冻融侵蚀强度评价模型,结合野外三维激光扫描观测结果初步探讨了冻融侵蚀时空分异规律对岩体产屑率的影响。研究结果表明:(1)大气温度、岩体结构、降水量、坡度、地震烈度和坡向等因素对冻融侵蚀强度的贡献值依次减小。(2)天山地区冻融侵蚀下界海拔约为2600~2900 m,冻融侵蚀的空间分布具有明显的垂直分带性和纬度坡降性,时间上具有明显的季节变化特征,融化和冻结交替时大气温度在冻融侵蚀基准线0 ℃上下波动频繁,冻融侵蚀最为强烈。(3)溜砂坡形成过程被划分为岩体冻融侵蚀产屑、岩屑运移和堆积3个阶段;花岗岩(硬岩)、砂岩(中硬岩)和千枚岩(软岩)斜坡产屑率随冻融侵蚀评价指数增加而增加,随岩石冻融系数增加而减小,建立不同岩性斜坡产屑率与冻融侵蚀强度和岩石冻融系数的定量关系式。该成果可以为冰缘山区岩体冻融侵蚀理论研究、工程建设及防灾减灾提供参考。