岩土边坡地震崩滑及其初判准则

根据我国过去近８００ 年间地震诱发天然岩土边坡崩滑的事例, 研究了我国岩土边坡地震崩滑的特征, 以及边坡地震崩滑与地震动参数的关系。通过对１２５ 次历史地震造成的２８５ 例典型滑坡进行分析, 提出了预测天然岩土边坡地震崩滑的初判标准。     

Analysis of landslide stability under seismic action and subsequent rainfall: a case study on the Ganjiazhai giant landslide along the Zhaotong-Qiaojia road during the 2014 Ludian earthquake,Yunnan, China

In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area.

     

Studies on passive flexible protection to resist landslides caused by the May 12, 2008, Wenchuan earthquake

The landslides caused by the 5.12 Wenchuan earthquake resulted in enormous casualties and property losses. Since the earthquake, more than 3,600 landslides have occurred, and 17 of them were catastrophic, each of which has killed more than 30 people. Meanwhile, passive flexible protection has gradually been introduced to resist landslides due to its significant advantages of economy, safety, and environmental protection. To resist landslides effectively, it is necessary to study the load path and design method of passive flexible protection under the action of landslides. In the design of passive flexible protection against landslides, determination of the landslide load is the primary task. In this paper, the formulas of the probability density function and distribution function of the landslide pressure are developed to obtain the value of the accumulated landslide pressure acting on the passive flexible protection, which can be used as the load input parameter in the design of passive flexible protection to resist landslides. Based on the case of the “Shiziliang” potential landslide for the 5.12 earthquake, the pressure data of the landslide are collected, the calculation formulas of the volume, and the pressure of the intercepted landslide are established, and the statistical parameters of the landslide pressure‐loading sample are obtained. According to the Kolmogorov–Smirnov test method, the loading sample of the landslide pressure obeys an extreme‐value type‐I distribution, and then the load model of the landslide pressure is determined. Based on the reliability analysis method, the standard value of the landslide pressure with an over‐95% assurance rate is obtained. These results can provide references for load confirmation to design the passive flexible protection to resist landslides.     

唐家山堰塞湖库区马铃岩滑坡地震复活效应及其稳定性研究

 马铃岩滑坡位于唐家山堰塞湖内上游约4 km的通口河左岸,在堰塞湖抢险过程中备受关注。在对滑坡基本地质条件和地震前、后变形破坏迹象现场地质调查基础上,对震后、尤其是唐家山堰塞湖形成后滑坡稳定性进行了系统分析和计算。计算结果表明,各种不同工况下震后滑坡整体稳定,只是靠上游侧前缘受地震、堰塞湖蓄水及泄水水位骤降等因素影响存在局部失稳,马铃岩滑坡不会对下游唐家山堰塞坝溃坝以及未来堰塞湖综合治理工程产生不利影响,但震后重建工作中应注意靠上游侧滑坡体前缘一带不稳定对坡体上数十户居民造成的潜在危害。就马铃岩及地震重灾区其他古滑坡体而言,地震对大型古滑坡复活主要受控于其地形坡度及微地貌特征,地形坡度40°以上以及由缓变陡的转折部位是古滑坡整体或局部容易被地震触发失稳的充分条件,并非所有的古滑坡体均会被地震诱发而整体复活。     

基于界面牛顿力测量的双体灾变力学模型研究

 地震和滑坡灾害是人类面临的2种主要地质灾害,严重威胁人类社会的安全。这两类地质灾害的本质是相同的,通常与沿着构造带(面)两侧块体的相对运动有关。然而,常规监测方法主要针对位移、水位等进行监测,这些参数是产生灾变的必要条件,而非充分条件,不能作为灾变预测的主要依据。通过实验室模拟研究,首先发现“牛顿力突降,灾变发生”的实验现象,证明2个块体相对运动的核心问题是构造带(面)上的牛顿力变化;其次,在此基础上建立基于牛顿力变化测量的双体灾变力学模型和数学表达,并提出牛顿力的测量方法;最后,利用自主研发的牛顿力变化远程监测预警系统,通过滑坡现场监测,证实“牛顿力突降,滑坡发生”的科学现象。     

Remote Sensing Observations of Landslides and Ground Deformation from the 2004 Niigata Ken Chuetsu Earthquake

In recent years, major developments in remote sensing have made it possible to use these technologies to document the effects of earthquakes. Specifically, high-resolution satellite imagery and three-dimensional laser scanning (LIDAR) can provide important observations of earthquake damage that supplement traditional observations from field reconnaissance. The 2004 Niigata Ken Chuetsu earthquake provided an opportunity to use remote sensing to document the distribution of landslides in the epicentral region through the use of high-resolution satellite imagery and to document the detailed three-dimensional geometries of several failures using LIDAR. The satellite imagery was acquired the day after the earthquake, but at very large acquisition angles that resulted in image distortion. Nonetheless, the satellite imagery accurately identified the landslide distribution in the epicentral region, although the total area of landslides was underestimated by about 25% as compared with traditional aerial reconnaissance because of the large acquisition angle for the satellite imagery. Terrestrial LIDAR was used to collect three-dimensional data at several failure sites, including two large rock slides and a railroad tunnel portal affected by ground deformation. The LIDAR data allowed for precise measurement of failure deformations and geometries, and provided digital terrain models that could be archived and used in future analyses. In the future, satellite imagery and LIDAR, as well as other remote sensing technologies, will play an increasing role in documenting and understanding the effects of earthquakes.     

GIS支持下基于层次分析法的汶川地震区滑坡易发性评价

 2008年5月12日14时28分,四川汶川发生了Ms8.0级大地震,地震诱发了数以万计的滑坡灾害。在大约48 678 km2的区域内,采用震后遥感影像解译并结合野外调查的方法,共解译出48 007个滑坡。应用GIS技术,建立了汶川地震诱发滑坡灾害及相关地形、地质空间数据库,分析了断层、岩性、高程、坡度、坡向、河流、公路等7个因素与滑坡分布的关系,应用滑坡面积百分比这一标准来分别衡量每个因素中各个级别对滑坡的影响程度;然后使用层次分析法对这7个参数进行权重分析;在GIS平台下对这些参数进行综合分析,通过分析结果将研究区内滑坡按易发程度分为极高易发区、高易发区、中易发区、低易发区与极低易发区5类,极高易发区与高易发区面积约8 211 km2,占研究区总面积的16.9%;最后,使用汶川地震滑坡数据库对研究结果进行检验,检验曲线表明分区效果良好,其中极高易发区与高易发区内实际发生滑坡面积为430 km2,占滑坡总面积的60.5%。     

A method for quick assessment of earthquake-triggered landslide hazards: a case study of the Mw6.1 2014 Ludian,China earthquake

Rapid assessment of the distribution of earthquake-triggered landslides is an important component of effective disaster mitigation. The effort should be based on both seismic landslide susceptibility and the ground shaking intensity, which is usually measured by peak ground acceleration (PGA). In this paper, we address this issue by analyzing data from the Mw6.1 2014 Ludian, China earthquake. The Newmark method of rigid-block modeling was applied to calculate the critical acceleration of slopes in the study area, which serve as measurement of slope stability under seismic load. The assessment of earthquake-triggered landslide hazard was conducted by comparing these critical accelerations with the distribution of known PGA values. The study area was classified into zones of five levels of landslide hazard: high, moderate high, moderate, light, and very light. Comparison shows that the resulting landslide hazard zones agree with the actual distribution of earthquake-triggered landslides. Nearly 70% of landslides are located in areas of high and moderately high hazard, which occupy only 17% of the study region. This paper demonstrates that using PGA, combined with the analysis of seismic landslide susceptibility, allows a reliable assessment of earthquake-triggered landslides hazards. This easy-operation mapping method is expected to be helpful in emergency preparedness planning, as well as in seismic landslide hazard zoning.

     

汶川地震诱发滑坡与地震动峰值加速度对应关系研究

 利用汶川地震获得的地震动记录及峰值加速度数据和收集整理的近3 000个崩滑点数据,对汶川地震诱发滑坡与地震动峰值加速度之间的对应关系进行研究,得到如下认识：(1) 地震动峰值加速度与地震诱发崩滑之间存在非常明显的正相关性,随峰值加速度增加,地震滑坡灾害也逐渐严重。(2) 在龙门山震区存在0.2 g的峰值加速度分界线,大于此值时,地震滑坡灾害比较严重。(3) 整个区域峰值加速度的下限为0.05～0.07 g,小于此值时,诱发滑坡的可能性很小。(4) 不同地质区域对应斜坡临界加速度有所不同,一般在0.05～0.15 g之间变化,平均为0.1 g,说明震区斜坡承受地震的水平较差;峰值加速度超过局部场地斜坡临界加速度后,诱发滑坡的可能性增加。得到的峰值加速度研究结果与其他研究结果较为一致,表明利用地震动参数研究地震滑坡具有很好的一致性。依据峰值加速度与地震滑坡的对应关系,可以对震后滑坡灾害作快速评估,也可以将其应用到地震滑坡灾害预测/区划工作中,与地震动峰值加速度区划形成很好的衔接。     

Numerical and safety considerations about the Daguangbao landslide induced by the 2008 Wenchuan earthquake

The 2008 Wenchuan earthquake resulted in a large number of fatalities and caused significant economic losses.Thousands of landslides,many of which are very large,were triggered by the earthquake.A majority of catastrophic landslides were distributed along the central Longmenshan fault system,at the eastern margin of the Tibetan Plateau.Some of the landslides resulted in sudden damming of rivers causing flooding,which in turn induced secondary sliding disasters.Among the most significant landslides,the Daguangbao landslide was the largest in volume with the maximum thickness.For this,a numerical model of the Daguangbao landslide,using the material point method(MPM),was developed to simulate the interaction of the seismic loads imposed on the slope.The numerical results then are compared with the post-earthquake profile.As a consequence of the landslide,a nearly vertical head scarp with a maximum height of about 700 m was generated.This is considered as a high risk situation that requires constant monitoring and evaluation.Finally,we propose a methodology based on Bayesian networks(BNs) to manage the risk associated with the stability of the rockwall at the Daguangbao landslide site.     

强震区断裂活动与大型滑坡关系研究

 活动断裂带与大型滑坡之间的关系一直是人们关注的热点问题。通过汶川Ms8.0级地震活动断裂和大型滑坡调查,阐述龙门山活动断裂带大型滑坡形成的地质背景,总结活动断裂带大型地震滑坡的分布特征、形态特征、启动特征和分段特征及其相关影响因素。基于野外调查资料,以龙门山中央断裂带谢家店子滑坡为例,采用离散元方法模拟分析滑坡的启动和快速运移过程,提出高速远程滑坡的致灾后果决定于启动方式、飞行路径和堆积特征3个方面。本项研究对于认识断裂活动与大型滑坡之间的关系以及滑坡成灾后果预测具有重要的指导作用。     

山体滑坡泥石流的地震力算法与防治

近来山体滑坡泥石流地质灾害频繁,而且与地震和降雨密切相关.因此提出常规地震力计算的一个改进算法,即在考虑地震加速度惯性力的同时再补充一项地震波持续振动产生的超静渗透力,它将减轻土体的有效重,更加容易滑坡.对于风化带乱石土层山坡,以平行坡面的直线滑动面为例,分别推导了下雨浸水饱和与非饱和情况下的浅层滑坡计算公式.经过比较不同坡比,地震加速度和超静渗透力的计算结果,常规计算不考虑超静渗透力时,抗滑安全系数会有高达25%的误差;当山坡下雨浸水饱和时,安全系数再减半,更易滑坡,在降雨迳流下必然形成泥石流.提出了几项防治措施,并介绍防治成功的工程实例.     

基于GIS的汶川地震滑坡灾害影响因子确定性系数分析

 2008年5月12日14时28分,四川省汶川发生了8.0级大地震,地震诱发了数以万计的滑坡灾害。在大约48 678 km2的区域内,采用震后航空像片与多源卫星影像解译并结合野外调查验证的方法,共圈定出48 007个地震滑坡灾害。在此基础上,选取地层、岩性、断裂、地震烈度、宏观震中、地表破裂调查点、地形坡度、坡向、顺坡向曲率、高程、水系与公路共12个影响因子作为汶川地震诱发滑坡影响因子,利用GIS强大的空间分析能力与确定性系数方法,对这12个影响因子进行敏感性研究。研究结果表明：(1) 寒武与震旦系是地震滑坡易发地层,侵入岩组、灰岩为主的岩组是地震滑坡发育的高敏感性岩组;(2) 地震滑坡受中央断裂影响最大,同时还受控于前山断裂,受后山断裂的影响较小;(3) 地震滑坡易发性分别随着地震烈度、与震中的距离、与地表破裂点距离的增加而减少;(4) 坡度大于40°是地震滑坡的易发坡度,E,ES方向为地震滑坡的易发坡向,高程范围为1 000～2 000 m,尤其是高程1 000～1 500 m范围为地震滑坡易发区;(5) 400 m水系缓冲区和2 000 m公路缓冲区范围内滑坡易发性较高。确定研究区内各地震滑坡影响因子最利于滑坡发生的数值区间,为进一步地震滑坡区域评价及预测奠定基础。     

利用强震记录分析汶川地震诱发滑坡

 根据Newmark方法提出一种在已知强震记录和滑坡数据的情况下,推导斜坡临界加速度的方法。采用这种方法,利用汶川地震中理县的3组强震记录数据和地震滑坡数据,得到沙坝台,桃坪台,木卡台附近区域的临界加速度估计值分别为40,50和70 gal。计算结果与灾区实际比较脆弱的地质情况一致。斜坡临界加速度可以作为利用地震动参数判定斜坡在地震作用下是否破坏变形的定量依据,为地震滑坡的定量研究提供一种思路。利用所提出的方法和汶川地震得到的大量强震记录,对龙门山地区的临界加速度进行评估,为震后恢复重建中的工程应用和地震滑坡灾害预测、区划工作提供定量参考信息。研究方法和结果有助于推动我国地震滑坡的定量化研究。     

黄土滑坡工程地质问题分析研究

近年来,黄土滑坡成为我国西北地区最为严重的地质灾害之一。随着工程活动的加强,黄土滑坡成为近年地质研究的热点问题。2012年在对麟游县一后侧山体滑坡进行了多次现场调查和滑坡特征测量后获得了详细的野外勘察资料。基于现场工作,初步分析了降雨、地下水、地震等导致滑坡机制,通过工程实例,归纳出有效地黄土滑坡治理方案。     

雅安地震区吴家山滑坡变形及稳定性分析

雅安地震引发昊家山地区老滑坡体发生失稳现象，安置GPS监测系统对该地区进行了变形监测。在区域地质条件基础上，运用极限平衡法分析坡体稳定性；利用FLAC3D三维显式有限差分程序建立模型，输入地震波分析地震作用下坡体的变形情况，并结合实际GPS监测结果，探讨变形规律。稳定性分析表明地震作用导致边坡稳定性大幅下降，引起了此次边坡变形失稳；同一地震作用下不同土层的动响应程度不同，老滑坡体对地震作用更加敏感；数值模拟结果揭示了地震作用下坡体的变形情况，与实际监测结果进行了对比分析，对研究坡体变形有借鉴意义。     

Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province,northwest China

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan’an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan’an Town with a total volume of about 6.06 × 10⁸ m³ are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper.     

Mapping the susceptibility of rainfall and earthquake triggered landslides along China–Nepal highways

The 2015 Gorkha earthquake (Mw?=?7.8) caused significant earthquake triggered landslides (ETL) in a landscape that is heavily intervened by rainfall triggered landslides (RTL). China’s Belt and Road Initiative plan to boost South-Asian regional trade and mobility through two key highway corridors, i.e. 1) Longmu–Rasuwa–Kathmandu (LRK) and 2) Nyalam–Tatopani–Kathmandu (NTK) route, that dissect the Himalayas through this geologically unstable region. To understand the spatial characteristics and susceptibility of these ETL and RTL, we delineate the landslides by means of time variant satellite imageries, assess their spatial distribution and model their susceptibilities along the highway slopes. We use a coupled frequency ratio (FR) – analytical hierarchy process (AHP) model by considering nine landslide determinants, e.g. geomorphic type (slope, aspect, curvature, elevation), hydrologic type (erosive potential of gullies, i.e. stream power index and distance to streams), normalized difference vegetation index, lithology and civil structure type (i.e. distance to roads). The results demonstrate that elevation and slope predominantly control both these landslide occurrences. The model predicts locations of ETL with higher accuracy than RTL. On comparison, NTK was safer with 133.5 km² of high RTL or ETL (or both) landslide susceptible areas, whereas LRK has 216.04 km². For mapping the extent of these landslides, we constricted it to the slope units of highways to reduce the computational effort, but this technique successfully achieved an acceptable threefold average model prediction rate of 82.75% in ETL and 77.9% in RTL. These landslide susceptibility maps and route comparisons would provide guidance towards further planning, monitoring, and implementing landslide risk mitigation measures for the governments.

     

Landslide-susceptibility mapping in a semi-arid mountain environment: an example from the southern slopes of Sierra Nevada (Granada,Spain)

Landslide susceptibility is analysed in a semi-arid mountain environment, on the southern slope of Sierra Nevada. In a study area of 460 km², 252 landslides were inventoried, affecting 3.2% of the total surface area. These landslides were mainly slides and flows on phyllite, schist and marble units in the Inner Zone of the Betic Cordillera. The most relevant determining factors proved to be elevation, slope angle, slope aspect and lithology. Triggering factors include mainly short-term landslide generation during heavy rainfall, as well as sporadic earthquakes or long-term activation by land-use changes, river over-excavation, etc. Although landslide susceptibility, assessed by the GIS matrix method, is predominantly low, some 15% of the study area shows moderate to very high susceptibility, coinciding with the sites of public works in the region. The map drawn was validated by the degree-of-fit method, registering values above 83.2% for the zones of high and very high susceptibility.     

基于离心振动台的堆积型滑坡加速度响应特征

 加速度响应规律是解释滑坡震害、合理确定地震影响系数的基础。为此,设计完成了50倍重力加速度条件下的堆积型滑坡离心振动台模型试验,用来研究堆积型滑坡的加速度响应特征及规律。模型滑坡放置于600 mm×400 mm×500 mm(L×W×H)的刚性模型箱内,采用汶川地震清溪台站反演的基岩波作为基底输入,调整其幅值,研究不同强度地震动作用下堆积型滑坡的加速度响应特征及规律。试验结果表明：坡面水平向和竖直向峰值加速度(PGA)放大系数随滑坡的高程增加而增大,趋于坡顶时,增速明显变大,具有明显的高程放大效应;地震动作用下坡面与坡体内部的加速度响应特征明显不同,具有坡面浅表放大效应;滑床岩体自下向上水平向加速度有放大趋势,但与滑坡浅表土体相比,放大倍数则明显减弱;坡顶附近存在显著的波型转换现象;随着输入地震波强度的增大,PGA放大系数总体上表现为递减趋势。所得到的成果初步揭示了堆积型滑坡的加速度响应特征,为解释滑坡震害、确定地震影响系数等提供较可靠的依据。