A quantitative approach for the evaluation of rockfall risk on buildings

Natural Hazards - A quantitative rockfall risk analysis at local scale is a complex and difficult task because it should consider both the randomness in the natural phenomenon and the variability...     

Quantitative assessment of the residual risk in a rockfall protected area

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d’Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d’Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10⁻⁴ to 9.1×10⁻⁷ and the societal risk from 1.5×10⁻² of annual probability of loss of life to 1.2×10⁻⁵.     

Event tree analysis for rockfall risk assessment along a strategic mountainous transportation route

A quantitative risk analysis has been performed in a tourist area of Sicily (Italy) with the aim of assessing the rockfall risk along an important transportation corridor, crossing a geologically complex area and poor rock masses. The procedure followed herein is based on an event tree analysis, which was properly customized to take into account the peculiarity of the area and of the road path. Rock mass surveys, trajectory simulations and probabilistic models are proposed with the aim of calculating the probability related to possible scenarios in case of rockfalls. Achieved outcomes demonstrate that such procedure, resulting from a multifaceted study, is a reliable tool, which can be taken as reference to calibrate further risk models in comparable contexts of the world, where rockfall threaten communication routes. This would represent a helpful instrument to the scientific community and to local authorities dealing with one of the most troublesome natural phenomena affecting the public safety.     

Empirical assessment of rockfall and debris flow risk along the Karakoram Highway,Pakistan

Natural Hazards - The Karakoram Highway links north Pakistan with southwest China. It passes through unique geomorphological, geological and tectonic setting. This study focused 200-km-long section...     

Flood loss analysis and quantitative risk assessment in China

Risk assessment is a prerequisite for flood risk management. Practically, most of the decision making requires that the risks and costs of all risk mitigation options are evaluated in quantified terms. Therefore, a quantitative assessment of possible flood loss is very important, especially for emergency planning and pre-disaster preparedness. This paper presents a preliminary methodology and an operational approach for assessing the risk of flood loss to the population, crops, housing, and the economy at county level in China. The present work assesses the risk of loss for each element (people, crops, and so on) under low-, moderate-, and high-intensity flood using intensity-loss curves and loss rates based on historical flood data from 1990 to 2008. Results show that the counties with high flood risk are primarily located in North, East, Central, and South China, particularly in the lower reaches of rivers. On the other hand, the risk of most counties in the western region is generally lower than that of counties in the eastern region. However, for the entire country, the high-risk regions have both a substantial amount of rainfall and low terrain, making such regions highly prone to flooding. Moreover, these high-risk regions present both high population and wealth density.     

GIS-based evaluation of rockfall risk along routes in Greece

This article presents a GIS-based system, designed to assist in the management of rockfall risk along Greek routes. The system was developed in two stages; the field data collection led to the implementation of a rockfall rating system with its fundamental parameters, while the data process concluded to a rockfall data base and a GIS-based interface. The fundamental parameters were derived from the rockfall hazard rating system developed by Pierson et al. at the Oregon State Highway Division and provide a coherent approach to decide the type and the cost of protection measures to be applied in an area affected by rockfalls and presents highest rockfall risk. The system presented in this paper as well as the original system comprises exponential scoring functions that represent the increased hazard and reflected in nine categories forming the classification. The method presented in this paper modified certain categories from the original system which were described qualitatively and may lead to quite subjective estimations. These categories are ditch effectiveness; climate and presence of water on slope as well as rockfall history. Moreover, the original category “Geologic characteristic” was changed to Structural and Discontinuities Index; an index that relates blockiness of rock mass and orientation of joints with their weathering condition and their roughness. This index follows the classification of weathering and joint’s roughness suggested by International Society of Rock Mechanics, while other modifications regarding the categories “decision sight distance” and “roadway width” were applied based on Greek standards. An application of this modified method to a 3 km road which connects Athinios port and Fira, the capital of Santorini island, Greece, a high traffic intensity road where rockfalls periodically cause traffic interruptions is presented. The method was applied in fifteen cross sections of slopes adjacent to the road and the analyses showed increased risk and the need for urgent remedial works.     

四川青川县碾子崩塌风险性评价

2008年5月12日四川省发生8级地震,地震对青川县造成了巨大破坏,同时引发了大量的次生地质灾害。本文以碾子村五社崩塌灾害点为研究评价对象,在工程地质条件、危岩体分布特征、变形破坏模式的研究基础之上,计算了研究区典型危岩体的稳定性及破坏概率。在野外滚石实验的基础上,运用专业软件模拟了失稳块石的运动轨迹,得到了落石运动过程中的速度、跳高及动能,并进一步确定了崩塌的影响范围。在野外调查和收集当地社会经济资料的基础上,对崩塌的易损性及风险性进行了评价,并根据灾害特点及评价结果提出了相应的防灾减灾措施。     

单体危岩崩塌灾害风险评价方法——以四川省丹巴县危岩崩塌体为例

综合分析国内外危岩崩塌风险评价方法的基础上,以丹巴县双拥路危岩崩塌体为例,提出了适用于单体危岩崩塌的风险评价方法。根据蒙特卡洛法的基本原理及方法编制了危岩崩塌体的稳定性可靠度分析程序,计算了不同工况下危岩失稳的概率。同时,考虑地面建筑物对落石的阻挡影响,利用专业软件模拟落石的运动轨迹,并根据研究区的地形地貌特点进一步确定了落石的影响范围。在野外调查和收集当地社会经济资料的基础上,开展了承灾体的易损性研究,对资产的易损性进行了评价。根据危岩失稳的概率及承灾体的易损性分析,进一步得到不同工况下落石影响区内承灾体的经济损失水平,对危岩崩塌灾害的风险进行了定量评价。风险评价的结果可为危岩崩塌灾害影响区的城镇建设和规划提供科学依据,从而有效地规避风险和减灾防灾。     

单体危岩崩塌灾害风险评价方法——以四川省丹巴县危岩崩塌体为例

综合分析国内外危岩崩塌风险评价方法的基础上,以丹巴县双拥路危岩崩塌体为例,提出了适用于单体危岩崩塌的风险评价方法。根据蒙特卡洛法的基本原理及方法编制了危岩崩塌体的稳定性可靠度分析程序,计算了不同工况下危岩失稳的概率。同时,考虑地面建筑物对落石的阻挡影响,利用专业软件模拟落石的运动轨迹,并根据研究区的地形地貌特点进一步确定了落石的影响范围。在野外调查和收集当地社会经济资料的基础上,开展了承灾体的易损性研究,对资产的易损性进行了评价。根据危岩失稳的概率及承灾体的易损性分析,进一步得到不同工况下落石影响区内承灾体的经济损失水平,对危岩崩塌灾害的风险进行了定量评价。风险评价的结果可为危岩崩塌灾害影响区的城镇建设和规划提供科学依据,从而有效地规避风险和减灾防灾。     

Choosing a rockfall barrier with the Precautionary Principle: a quantitative approach

The paper illustrates an approach for implementing the Precautionary Principle in risk management, exemplified by a procedure aimed at choosing the height of a rockfall barrier protecting a railway stretch. Risk is expressed by the frequency f of blocks hitting the railway—i.e. by the ratio between the number of blocks reaching the railway and the number of blocks falling from the slope—assessed through software simulation of the falling of the blocks. The height from which a block may fall is considered to be the main uncertainty factor in risk estimation, which translates into uncertainty as to the level of risk, as every simulation shows that more than one impact frequency is possible. Such uncertainty justifies the precautionary approach to the design of the barrier, and is represented mathematically by means of possibility and probability distribution functions. The distributions make it possible to express the degree of precaution related to a barrier as the level of confidence, in terms of necessity or probability measures—that can be placed on the fact that, because of the barrier, the impact frequency, although uncertain, will not exceed what is acceptable. It will be shown that the degree of precaution takes quite different values if possibility theory is used instead of probability theory. Finally some simple cost/benefit analyses, that explicitly and quantitatively consider the degree of precaution, are exemplified.     

单体滑坡灾害财产风险定量评估模型

目前承灾体易损性评估尚处于经验评估阶段,制约了单体滑坡灾害财产风险评估的定量化程度。为此,针对典型承灾体（建筑结构物）,提出一种单体滑坡灾害财产风险评估模型。认为财产风险是坡体失稳概率、承灾体在滑坡作用下的失效概率以及承灾体价值的乘积。避开了易损性评估,从一个新的角度来评估滑坡灾害财产风险。通过研究,验证了该模型正确反映了滑坡成灾过程中各种因素对财产风险的影响,从而为单体滑坡灾害财产风险的定量化评估提供了新的途径。另外以该模型应用研究为基础,提出承灾体安全范围的概念,对于每一个承灾体而言,将单体滑坡灾害影响范围划分为：危险区域、相对危险区域和安全区域,为建设工程选址或场地风险评估提供了实用指标,具有一定的工程实用价值。     

Uncertainty in dam safety risk analysis

The character and importance of uncertainty in dam safety risk analysis drives how risk assessments are used in practice. The current interpretation of uncertainty is that, in addition to the aleatory risk which arises from presumed uncertainty in the world, it comprises the epistemic aspects of irresolution in a model or forecast, specifically model and parameter uncertainty. This is true in part but it is not all there is to uncertainty in risk analysis. The physics of hazards and of failure may be poorly understood, which goes beyond uncertainty in its conventional sense. There may be alternative scenarios of future conditions, for example non-stationarity in the environment, which cannot easily be forecast. There may also be deep uncertainties of the type associated with climate change. These are situations in which analysts do not know or do not agree on the system characterisation relating actions to consequences or on the probability distributions for key parameters. All of these facets are part of the uncertainty in risk analysis with which we must deal.     

A statistical approach to landslide risk modelling at basin scale: from landslide susceptibility to quantitative risk assessment

A procedure for landslide risk assessment is presented. The underlying hypothesis is that statistical relationships between past landslide occurrences and conditioning variables can be used to develop landslide susceptibility, hazard and risk models. The latter require also data on past damages. Landslides occurred during the last 50 years and subsequent damages were analysed. Landslide susceptibility models were obtained by means of Spatial Data Analysis techniques and independently validated. Scenarios defined on the basis of past landslide frequency and magnitude were used to transform susceptibility into quantitative hazard models. To assess vulnerability, a detailed inventory of exposed elements (infrastructures, buildings, land resources) was carried out. Vulnerability values (0–1) were obtained by comparing damages experienced in the past by each type of element with its actual value. Quantitative risk models, with a monetary meaning, were obtained for each element by integrating landslide hazard and vulnerability models. Landslide risk models showing the expected losses for the next 50 years were thus obtained for the different scenarios. Risk values obtained are not precise predictions of future losses but rather a means to identify areas where damages are likely to be greater and require priority for mitigation actions.     

Suitability of airborne laser scanning for the assessment of forest protection effect against rockfall

Rockfall simulation models are now able to quantify the protective effect of forest with the integration of rock impacts on trees. Those models require spatially explicit forest characteristics which are costly to acquire in operational conditions. The present study compares rockfall simulation results obtained with different forest input data sources: field data with different levels of spatial detail and two methods based on airborne Lidar data. Three different forest stands are tested with several virtual terrain configurations. When rockfall energies are below 200 kJ, the forest protection effect is significant. For higher energies, it also exists but it is minor compared to the effects of topography and rock volume. For all forest input data sources, the estimated rockfall intensity is within ?13 and 16 % of the reference value, whereas the frequency is generally overestimated. Both Lidar methods yield a satisfactory forest protection effect evaluation, but single tree detection tends to underestimate it. Improvements are possible regarding the spatial heterogeneity of stem density and the diameter distribution by tree species.     

崩塌体稳定性检算方法优化研究

针对现有崩埸体稳定性检算方法存在的问题，对倾倒式和错断式两种崩塌体的稳定性检算方法进行了修正，指出倾倒式破坏只考虑底部与稳定岩体断开的情况是不全面的；错断式破坏的破坏面确定不能按最大剪应力原理确定，而应遵循摩尔-库仑准则。建立了相应修正的稳定性检算方法，通过检算实例与原方法比较发现，对倾倒式检算，如果底部连接时，原方法考虑过于安全，不适用于底部连接的情况；对错断式检算，原检算方法偏于不安全，特别是当崩埸体底部岩体节理裂隙发育或有不利结构面存在时。     

Analysis of rockfall risk on mountainside roads: evaluation of the effect of protection devices

Many kilometres of roads are close to rock slopes that are prone to rockfalls. The fulfilment of safety requirements in such situations is a multidimensional design process involving public and private technicians in the assessment and management of the problem. In this paper, a rockfall risk management approach has been applied to the road infrastructure network of the Regione Autonoma Valle D’Aosta, in order to calculate the level of risk and of its reduction using rockfall protection devices. In order to better understand the methodology, a comparative analysis of road accidents in Aosta Valley has been discussed. The road risk assessment was developed taking into account the absence of rockfall protection devices, and when they are present, different levels of efficacy have been considered.     

Landslide risk assessment

Landslide risk can be assessed by evaluating geological conditions associated with past events. A sample of 2,4 16 slides from urban areas in West Virginia, each with 12 associated geological factors, has been analyzed using SAS computer methods. In addition, selected data have been normalized to account for areal distribution of rock formations, soil series, and slope percents. Final calculations yield landslide risk assessments of <0.50=low risk, 0.50 to 1.50=moderate risk, and >1.50=high risk. The simplicity of the method provides for a rapid, initial assessment prior to financial investment. However, it does not replace on-site investigations, nor excuse poor construction.     

滚石冲击力测试研究

以国内外代表性滚石冲击力计算方法为基础,针对冲击力的影响因素,设计了一套滚石冲击力测试装置。通过试验设计,选取不同的滚石质量、冲击速度、入射角度、缓冲材料性质及厚度等影响因素,获得冲击力变化规律。结果表明：最大冲击力随滚石重量的减小或冲击速度的降低而逐渐减小,2 cm厚度缓冲层比直接冲击时减小了90%左右,缓冲效果明显。同时最大冲击力随着入射角度的变小而降低,但入射角度越小,冲击力值降低的幅度越小。结合冲击试验结果,通过冲击力计算方法对比分析,建立了可用于各影响因素的最大冲击力计算方法,验算表明误差很小。研究结果可为滚石灾害的防治设计提供参考依据。     

A review of flexible protection in rockfall protection

Natural Hazards - Natural hazards, such as high winds, heavy rains and ice melting, can easily trigger the rockfall which usually leads to great personal injuries and property loss; therefore, the...