A method for assessing and managing landslide residual hazard in urban areas

On February 14, 2010, a large landslide affected the urban centre of San Fratello town (Sicily Island, Southern Italy), causing severe damage to buildings, roadways, and infrastructure, as well as about 2000 evacuees. This large complex landslide, covering more than 1 km² in extension, represents one of the major phenomena that ever occurred in Sicily. In order to manage the landslide risk, the civil protection system was activated as part of the initial response to the emergency (the “emergency phase”). This involved the Civil Protection Departments both at national (DPC) and regional (DRPC) levels, as well as scientific institutions (namely “Competence centres”, CdCs), local administration personnel, and technicians. On March 8, 2010, during the post-event recovery phase, a ground-based synthetic aperture radar (GB-InSAR) system was installed in order to monitor the ground surface deformation, assess the landslide residual risk, and analyse its displacement trend. Accurate field surveys and building inspections were also performed for a validation of the GB-InSAR data, in order to map the ground deformation, plan building evacuation-demolishment, as well as check the efficiency of the landslide mitigation works. This paper describes the outcomes of the 57 month monitoring campaign (March 2010–December 2014), reporting the use of GB-InSAR data for near real-time monitoring, mapping, and post-emergency/recovery management activities. The final aim was to provide the civil protection personnel with a reliable, rapid, and easy communication system of the monitoring results, designed to an enhance understanding of the landslide phenomena, and to support the decision-making process.     

基于降雨过程自动识别的泥石流实时预警技术

本文结合对雨量数据的分析, 总结了泥石流自动实时监测预警中的一些关键技术, 并提出一种基于降雨过程的泥石流实时监测预警的解决方案。在泥石流的监测预警工作中, 目前多采用雨强与累计雨量作为主要参数, 如何正确识别一场降雨过程, 对于提高监测预警的精度具有重要的意义。结合监测数据特征, 本文采用詹钱登对降雨过程的划分标准, 基于数据库技术实现对降雨过程的自动识别, 为后续预警参数的获取提供支撑。由于受雨量计工作模式的影响, 其原始数据的时间间隔是随机的, 不能直接用于预警模型的计算, 因此对雨量监测数据进行等时间间隔的处理。在预警流程方面, 如何实现预警过程无人工干预的完全自动、实时与稳定运行, 一直是预警工作中的难点, 本研究中引入“系统服务”这一技术, 将整套预警系统作为系统级别的后台服务运行于服务器上, 能够保证整个预警过程稳定地运行, 真正意义上实现了泥石流监测预警过程的自动化与实时化。本文研究成果应用于走马岭沟泥石流监测预警中, 成功对2013年7月8日的泥石流事件进行预警。     

滑坡对降雨响应的多指标监测及综合预警探析:以赣南罗坳滑坡为例

降雨量和位移是当前降雨型滑坡监测预警最常用的指标。然而,降雨量和位移监测结果只能反映降雨作用下滑坡的变形情况,不能揭示滑坡内在物理力学性状对降雨的响应。因此,除降雨量和位移监测之外,建立包括体积含水率、基质吸力等反映滑坡动态演化过程的关键指标监测体系必将成为今后更真实地把握滑坡内在演化趋势、更准确地建立滑坡综合预警判据的最有效手段。笔者对赣南地区典型降雨型滑坡进行了多指标监测及综合预警示范研究。结果表明:(1)在降雨条件下滑坡土体内部体积含水率、基质吸力和温度等多指标均产生有规律的动态响应;(2)随着降雨的持续,滑体体积含水率与基质吸力的变化均具有显著的滞后现象;(3)体积含水率和基质吸力变化速率与滑体位移具有显著的正相关性;(4)滑体温度分布变化规律受大气温度和体积含水率的共同影响。以实测数据的滑坡稳定性分析为基准,在考虑实际降雨入渗深度与滑坡稳定性的关联度上,建立了包括日降雨量、体积含水率增加速率、基质吸力减小速率以及位移速度多元指标预警方法体系,提出了基于关键指标综合预警体系及确定方法,旨在为降雨滑坡准确预警提供新模式。     

基于位移比模型的三峡库区云阳县域内蠕变型滑坡降雨预警

建立高效合理的区域滑坡灾害降雨预警模型对滑坡防治具有重要意义.然而以往的研究多侧重于临滑预警,对蠕变型滑坡在强降雨工况下的短暂加速变形的预警研究还有待深入.以三峡库区云阳县域内滑坡为例,首先根据滑坡地表位移监测数据的特点对统计样本进行合理筛选.再通过降雨因子与滑坡发生的相关性分析以及对滑坡在降雨条件下位移变化情况的数值模拟,确定了适用于不同时间阶段的降雨统计变量.然后将考虑了滑坡规模特征的滑坡位移比（累计位移与滑坡纵长之比）作为变形指标,分时段统计滑坡地表位移监测数据与历史降雨信息,建立了日降雨数据与月位移数据的对应关系,得到了可用于确定降雨量阈值的位移比模型,并获得了云阳县蠕变型滑坡的五级预警分区.最后分别选用研究区滑坡险情实例、长年位移监测数据及极端降雨事件对模型预警效果进行检验.结果显示基于专业监测数据的位移比模型的滑坡降雨预警结果与实际情况相符,可为蠕变型滑坡的预警预报提供依据.      

降雨诱发滑坡阶跃型变形的预测分析及应用

滑坡进入蠕动变形阶段之后,往往难以及时开展勘察治理工作,合理的临灾预警是有效减少滑坡灾害损失的重要手段。首先确定降雨诱发“阶跃型”滑坡的预警关键判据为前期降雨、当次降雨、位移速率,并引入“一个降雨过程”定义滑坡监测的降雨区间,将预警过程分为当次降雨和前期降雨+当次降雨两种模式。然后运用最小二乘法确定滑坡“阶跃”变形曲线上的“破坏拐点”和“稳定拐点”用以确定变形加速区间,以此求解前期降雨、当次降雨以及移速率阈值。最后以王家坡滑坡为例,设计了两种模式下的5级递进式分级预警模型。研究表明：（1）前期降雨与当次降雨组成“一个降雨过程”的时间间隔为7 d;（2）王家坡滑坡的位移速率阈值为20 mm/d;（3）前期降雨+当次降雨模式下王家坡滑坡的前期降雨、当次降雨阈值分别为10、15 mm,当次降雨模式下王家坡滑坡的降雨阈值为25 mm。     

Displacement patterns of a landslide affected by human activities: insights from ground-based InSAR monitoring

Landslides interacting with large infrastructures represent a major problem for the economy, society as a whole, and the safety of workers. Continuous monitoring for 23 months using an integrated platform with a ground-based SAR interferometer (GB-InSAR), a weather station, and an automatic camera gave us the opportunity to analyze the response of an unstable slope to the different phases of work. The deformational behavior of both the natural slope and the man-made structures was recorded and interpreted in relation to the working stages and the rainfall conditions during the whole monitoring period. A typical pattern of displacement was identified for shallow landslides, debris produced by the excavation and gabions, metallic walls, and anchored bulkheads. Furthermore, insights into the dynamics and behavior of the slope and the man-made structures that interact with the landslide were obtained. Extreme rainfall is the main trigger of shallow landslides and gabion deformations, while anchored bulkheads are less influenced by rainfalls. Movement of debris that is produced by excavations and temporary metallic barrier deformation are closely related to each other. The herein proposed monitoring platform is very efficient in monitoring unstable slopes that are affected by human activities. Moreover, the recorded patterns of displacement in the slope and the man-made structures can be used as reference data for similar studies and engineering designs.     

Real-time monitoring and early warning of landslides at relocated Wushan Town,the Three Gorges Reservoir,China

A special monitoring and warning system has been established and improved in the Three Gorges Reservoir area since 1999. It is necessary to develop a real-time monitoring system on landslides because there are dense populations centered in the reservoir area and geo-hazards may be triggered by a 30-m water level fluctuation between 145 and 175 m in elevation during reservoir operation; the regular monitoring could not be suitable to the early warning on landslides. Since 2003, the authors have carried out a real-time monitoring and early warning project on landslides at the relocated Wushan town in the Three Gorges Reservoir area. The monitoring station includes Global Positioning System with high-accuracy double frequency to monitor ground displacement, time domain reflection technology, and immobile borehole, inclinometer to monitor deep displacement, piezometer to monitor pore water pressure, and precipitation and reservoir water level monitoring. Compared with traditional methods, the real-time monitoring is continuous and traceable in the acquisition process, and the cycle of data acquisition is very short, usually within hours, minutes, or even shorter. Based on the landslide monitoring experience at the Three Gorges Reservoir area, the early warning criteria on landslide are established in which the critical situation is classified into four levels: blue, yellow, orange, and red, respectively, expressed by no, slight, moderate, and high risk situation. Comprehensive judgment from multimonitoring data of Yuhuangge landslide in this area since 2004 suggested that the new Wushan town will be at the blue early warning level, although some monitoring data of individual displacement at deep borehole showed that the displacement was increased by 5 mm in 5 months with an average velocity of 1.0 mm/month, and the data of BOTDR also showed an obvious dislocation along a stairway on the landslide.     

Ground-based SAR interferometry for monitoring mass movements

An innovative technique for the remote assessment of ground displacements, based on radar interferometry and implemented using ground-based instrumentation (GB-InSAR), has been tested in recent years on a number of selected case sites. The system, known as LISA, developed by the Joint Research Centre (JRC) of the European Commission, is a ground-based radar interferometer specifically designed for field use. It is composed of two radar antennas mounted on a linear rail which horizontally slides to form a synthetic aperture. Coherent SAR processing converts the raw data into an image containing, for each pixel, information on the wave phase, which depends on the target-sensor distance. Consecutive couples of SAR images can be cross-correlated to form interferograms representing phase variations which can be directly related to ground displacement along the sight-line of the radar system, since they are acquired from exactly the same position. Several applications of the system have been conducted on a number of mass movements located in Italy, in order to validate the technique for the monitoring of landslides. GB-InSAR has proved its potential for the measurement of the superficial ground displacements of different landslide types, in terms of failure mechanism, materials involved, kinematics, water content and deformation rates. In particular conditions, such as fast-moving phenomena and inaccessible areas, the technique can be employed directly as a monitoring tool, providing multi-temporal displacement maps of the observed area. Additionally, some applications of the GB-InSAR have provided a fundamental support to decision makers during landslide emergencies, allowing the civil protection authorities to assess the risk and to manage an effective emergency response.     

地基InSAR技术及其典型边坡监测应用

为了开展边坡活动实时监测,研究以IBIS-L地基InSAR系统为代表的地基InSAR形变时序分析关键技术,进行针对不同变形特征的观测方案和数据处理方法的优化,并开展了奉节大树场镇灾后滑坡、神农架林区人工不稳定斜坡和备战铁矿露天采矿边坡等边坡活动的监测应用,以及备战铁矿隧道南口冰川运动的监测试验。4种类型边坡地基InSAR监测结果表明,在复杂工作情况下,地基InSAR设备具有较高的观测稳定性,在满足观测条件的情况下,地基InSAR测量精度能达到亚mm级,已成为监测边坡微小形变的重要技术手段。这扩展了形变监测模式从星载InSAR技术的“大尺度、宽覆盖”走向地基InSAR技术的“小尺度、局部精细测量”,进一步丰富了科研人员对边坡变形现象的动力学过程认识,为“星-地”联合InSAR技术监测地表形变过程奠定了技术基础。     

基于物理模拟试验的岩质滑坡地表位移分析

三段式岩质滑坡是一种典型的斜坡变形破坏模式,运用二维地质力学加载系统对其变形破坏全过程进行物理模拟试验研究,采用激光位移计对坡顶和坡脚位置进行位移监测。结果表明:位移监测曲线总体上表现为锁固段经历长时间的能量积累与应力调整后的突发脆性破坏;由于软弱夹层具有蠕滑特性,前缘蠕滑阶段呈现出与土质滑坡相似的初始变形→等速变形→加速变形特征;后缘拉裂阶段作为最短暂的变形阶段,其位移监测曲线表现为“减-增-减-增”的“W”型变化趋势;锁固段是三段式岩质边坡维持稳定的关键所在,其受剪变形的顺序为先上后下,损伤变形由端部向中部递进,最终锁固段剪断形成突发脆性破坏,滑坡高速启动。     

Rainfall duration and debris-flow initiated studies for real-time monitoring

A rainfall-induced debris flow warning is implemented employing real-time rain gauge data. The pre-warning for the time of landslide triggering derives the threshold or critical rainfall from historical events involving regional rainfall patterns and geological conditions. In cases of debris flow, the time taken cumulative runoff, to yield abundant water for debris triggering, is an important index that needs monitoring. In gathered historical cases, rainfall time history data from the nearest rain gauge stations to debris-flow sites connected to debris flow are used to define relationships between the rainfall intensity and duration. The effects by which the regional rainfall patterns (antecedent rainfall, duration, intensity, cumulative rainfall) and geological settings combine together to trigger a debris-flow are analyzed for real-time monitoring. The analyses focused on 61 historical hazard events with the timing of debris flow initiation and rainfall duration to burst debris-flow characteristics recorded. A combination of averaged rainfall intensity and duration is a more practical index for debris-flow monitoring than critical or threshold rainfall intensity. Because, the outburst timing of debris flows correlates closely to the peak hourly rainfall and the forecasting of peak hourly rainfall reached in a meteorological event could be a valuable index for real-time debris-flow warning.     

降雨诱发深层老滑坡复活变形的动态作用机制

强降雨易引发大型深层老滑坡的复活变形,研究其作用机制对建立滑坡变形破坏的降雨阈值,实现滑坡灾害的预警预报具有重要意义.以三峡库区秭归县谭家湾大型深层老滑坡为例,在地表宏观裂缝时空分布规律的精细描述基础上,结合15年的人工监测和2年的实时监测数据,分析了老滑坡的复活变形特征和发展过程.通过滑坡阶跃阶段的位移与降雨（当前降雨和前期降雨）的相关性分析,提出了降雨对深层滑坡复活变形演化过程的动态作用机制.谭家湾滑坡的7次“阶跃”变形与强降雨相关,但累积位移增量与累积降雨量无明显正相关关系,水平位移增量基本相同时,累积降雨量明显不同.引起第一次阶跃变形的累积降雨量和最大日降雨量均明显大于后续阶段,可能受控于强降雨的作用机制由“孔隙渗流”为主,逐渐转变为“渗透性增加的孔隙渗流+裂隙优势流”的综合渗流模式.这对进一步深入研究强降雨诱发深层老滑坡阶跃变形的内在机理与灾害预警具有一定的理论意义和参考价值.      

Monitoring, prediction, and early warning using ground-based radar interferometry

In order to define adequate prevention measures and to manage landslide emergencies, real-time monitoring is required. This paper presents two different applications of the remote sensing technique: the ground-based synthetic aperture radar interferometry, here proposed as a monitoring and early warning support for slope instability. Data acquisitions carried out through a ground-based synthetic aperture radar interferometer, operating in K_u band, installed in front of the observed slopes, are discussed. Two case studies, based on the use of the same apparatus (formerly developed by the Joint Research Center of the European Commission and by Ellegi-LiSALab srl), are reported: the first one concerns the monitoring of a large landslide, named Ruinon (Valfurva, Italy). The second one deals with the monitoring of the NW unstable slope in the Stromboli island aimed to implementing an early warning system. Acquired interferometric data are processed to provide displacements and velocity maps of the monitored area. The monitoring services ongoing on the Ruinon landslide and on Stromboli demonstrate the capability of this technique to operate in different operative settings (i.e., different phenomena and geological framework) and for different aims (monitoring for prevention, early warning, and emergency assessment). This methodology has also been proved by national and regional authorities of civil protection in order to provide a real-time monitoring for emergency management.     

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.     

An integrated methodology for landslides’ early warning systems

Early Warning Systems (EWS) are efficient tools for preventing and mitigating the risks associated to landslides occurrence. In this paper, an integrated methodology for landslides’ analysis is presented and described. Such methodology is aimed at the creation of early warning systems and is based on the integration between a modern monitoring technique, such as the Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR), along with advanced numerical modelling. The paper also shows the application of the proposed methodology to the case study of a rockslide in central Italy. The integration between monitoring data, thanks to a GBInSAR survey and advanced numerical simulations with the combined Finite-Discrete Elements Method (FDEM), allowed for the definition of a set of surface velocity thresholds to be adopted for the long-term monitoring of the landslide and for the creation of an effective EWS.     

Improving debris flow monitoring in Taiwan by using high-resolution rainfall products from QPESUMS

Debris flow is commonly initiated by torrential rain and its triggering is correlated to the hydrological, geological, and geomorphic conditions on site. In spite of the important effects of geology and topography, rainfall characteristic is the main external triggering factor to debris flow and is a predominant parameter for real-time monitoring. Due to the scarcity of sufficient spatial ground-based rainfall data in hill areas, quantitative precipitation estimation using remote-sensing techniques such as radar and satellite is needed for debris flow pre-warning. The QPESUMS (Quantitative Precipitation Estimation and Segregation Using Multiple Sensors) system was acquired to retrieve spatial rainfall data during the rainfall period from June 30 to July 6 in 2004 when Typhoon Mindulle and southwesterly flow struck Taiwan. The retrieved data were used for setting up the debris flow monitoring algorithm. With the aid of multiple platforms of meteorological observations, a rainfall threshold isohyet in a pilot area was mapped for debris flow monitoring. The rainfall monitoring algorithm based on QPESUMS provides more detailed information than the limited number of ground-based rainfall stations for interpreting the spatial distributions of rainfall events, and therefore is more suitable for debris-flow monitoring.     

Definition and performance of a threshold-based regional early warning model for rainfall-induced landslides

A process chain for the definition and the performance assessment of an operational regional warning model for rainfall-induced landslides, based on rainfall thresholds, is proposed and tested in a landslide-prone area in the Campania region, southern Italy. A database of 96 shallow landslides triggered by rainfall in the period 2003–2010 and rainfall data gathered from 58 rain gauges are used. First, a set of rainfall threshold equations are defined applying a well-known frequentist method to all the reconstructed rainfall conditions responsible for the documented landslides in the area of analysis. Several thresholds at different exceedance probabilities (percentiles) are evaluated, and nine different percentile combinations are selected for the activation of three warning levels. Subsequently, for each combination, the issuing of warning levels is computed by comparing, over time, the measured rainfall with the pre-defined warning level thresholds. Finally, the optimal percentile combination to be employed in the regional early warning system, i.e. the one providing the best model performance in terms of success and error indicators, is selected employing the “event, duration matrix, performance” (EDuMaP) method.     

基于主控因子分析与GM-IAGA-WNN联合模型的平推式滑坡位移预测研究——以垮梁子滑坡为例

滑坡位移预测模型是滑坡预警系统建立的核心,而模型可靠性与精确性关键在于主控因子的选取与基础理论模型的构建。学者们通过大量滑坡实例研究,已取得了诸多成果,但是由于滑坡位移变化具有强烈的个性特征及趋势发展的不确定性问题,在多因子联合作用下的位移预测模型尚有不足之处。本文以西南地区普遍存在的平推式滑坡——垮梁子滑坡为研究对象,结合前人已有的研究成果,综合考虑坡体内外各项影响因子,利用灰色关联度与相关性分析对坡体变形主控因子进行优化筛选。以此为基础,提出一种基于GM（1,1）灰色模型与改进型自适应遗传算法（IAGA）进行优化的小波神经网络（WNN）联合预测模型构建方案。通过对垮梁子滑坡历时5年的监测数据挖掘分析,得知滑坡变形受累计降雨、渗压、地下水位及土体含水率影响显著,预测结果与实际监测比较吻合。相较于传统BP神经网络模型、小波神经网络模型和未优化遗传算法-小波神经网络联合模型,该联合模型具有更好的稳定性与精度优势,在滑坡预警预报研究中具有良好的应用前景。     

突发型黄土滑坡监测预警理论方法研究——以甘肃黑方台为例

灌溉诱发的黄土滑坡大多数具有明显的突发性特征;斜坡破坏过程变形量小,历时短,具有较大的危险性。由于此类黄土滑坡加速变形阶段经历时间较短,GNSS系统和裂缝计等传统监测手段难以获取加速变形阶段系统完整的监测数据,更难以提前预警。针对这一难题,自主研发了自适应智能变频裂缝仪,它能够根据滑坡变形快慢自动调整采样频率。基于获取的黑方台多个突发型黄土滑坡的全过程变形-时间曲线,对这些变形曲线特征和规律进行分析研究,建立了针对性的黄土滑坡综合预警模型。将变形速率阈值和改进切线角作为滑坡预警的重要指标,建立了4级预警判据,通过自主研发的"地质灾害实时监测预警系统"实现滑坡的实时自动预警,并将预警信息与当地的群防群测信息平台对接,为防灾应急避让提供直接依据。2017年以来已先后6次对黑方台黄土滑坡实施成功预警,避免了重大人员伤亡,取得显著的防灾减灾效果。     

A cross-border regional earthquake early warning system: PRESTo@CE<Superscript>3</Superscript>RN

Since 2002 the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) in Udine (Italy), the Agencija Republike Slovenije za Okolje (ARSO) in Ljubljana (Slovenia) and the Zentralanstalt für Meteorologie und Geodynamik (ZAMG) in Vienna (Austria), are collecting, analyzing, archiving and exchanging seismic data in real time, initially in the framework of the EU Interreg IIIa Italia-Austria project “Trans-national seismological networks in the South-Eastern Alps”. As outcome of the successful cooperation, in the 2013 OGS, ARSO and ZAMG decided to officially merge their seismic monitoring efforts into the “Central and Eastern European Earthquake Research Network—CE³RN”. This work reports the results of a nine-month real-time test of the earthquake early warning (EEW) algorithm probabilistic and evolutionary early warning system carried out at the CE³RN. The study allowed identifying the actions to be implemented in order to let the CE³RN become in the next future an efficient cross-border EEW system.