Rockfall hazard assessment along a road in the Sorrento Peninsula,Campania, southern Italy

Rockfalls are common in the steep and vertical slopes of the Campania carbonate massifs and ridges, and frequently represent the main threat to the anthropogenic environment, potentially damaging urban areas, scattered houses, roads, etc. Despite the generally limited volumes involved, the high velocity of movement (from few to tens of metres per second) poses rockfalls among the most dangerous natural hazards to man. Evaluating the rockfall hazard is not an easy task, due to the high number of involved factors, and particularly to the difficulty in determining the properties of the rock mass. In this paper, we illustrate the assessment of the rockfall hazard along a small area of the Sorrento Peninsula (Campania region, southern Italy). Choice of the site was determined by the presence of a road heavily frequented by vehicles. In the area, we have carried out detailed field surveys and software simulations that allow generating simple rockfall hazard maps. Over twenty measurement stations for geo-mechanical characterization of the rock mass have been distributed along a 400-m-long slope of Mount Vico Alvano. Following the internationally established standards for the acquisition of rock mass parameters, the main kinematics have been recognized, and the discontinuity families leading to the different failures identified. After carrying out field experiments by artificially releasing a number of unstable blocks on the rock cliff, the rockfall trajectories along the slope were modelled using 2-D and 3-D programs for rockfall analysis. The results were exploited to evaluate the rockfall hazard along the threatened element at risk.     

Seismic-induced rockfalls and landslide dam following the October 30, 2016 earthquake in Central Italy

On October 30, 2016, a seismic event and its aftershocks produced diffuse landslides along the SP 209 road in the Nera River Gorge (Central Italy). Due to the steep slopes and the outcropping of highly fractured and bedded limestone, several rockfalls were triggered, of which the main event occurred on the slope of Mount Sasso Pizzuto. The seismic shock acted on a rock wedge that, after an initial slide, developed into a rockfall. The debris accumulation blocked the SP 209 road and dammed the Nera River, forming a small lake. The river discharge was around 3.6 m³/s; the water overtopped the dam and flooded the road. By a preliminary topographic survey, we estimated that the debris accumulation covers an area of about 16,500 m², while the volume is around 70,000 m³. The maximum volume occupied by the pre-existing talus mobilized by the rockfall is about 20% of the total volume. Besides blocking the road, the rockfall damaged a bridge severely, while, downstream of the dam, the water flow caused erosion of a road embankment. A rockfall protection gallery, a few hundred meters downstream of the dam, was damaged during the event. Other elastic nets and rigid barriers were not sufficient to protect the road from single-block rockfalls, with volumes around 1–2 m³. Considering the geological and geomorphological conditions, as well as the high seismicity and the socioeconomic importance of the area, a review of the entire rockfall protection systems is required to ensure protection of critical infrastructure and local communities.     

青海玉树断裂带地震落石的地震地质意义

2010年青海玉树Ms 7.1级大地震引发了一系列次生地质灾害,其中地震落石是除地震滑坡外沿断裂带及其邻侧最常见的现象。对玉树震区落石的调查发现,该区多处存在非常典型的多期地震落石分布现象,指示该区地震落石的发育与其他古地震现象类似,具有多期性和一定的原地复发性。实地调查表明,该区地震落石分布的主要特征为:多集中发育在活动断裂带附近的陡峭基岩斜坡下方,分布零散,且滚动较远,并常与古地震滑坡相伴生。初步获得的8个地震落石钙膜U系测年结果分布在距今6030±300a BP、4720±210a BP、3530±490~3560±280a BP、2010±160a BP、1090±70a BP、760±20a BP和230±20a BP年龄段,与该区古地震探槽和滑坡反映的地震事件比较吻合,进一步揭示玉树断裂带附近在全新世中晚期发生过多期可导致地表产生地震落石的事件。同时也说明,地震落石及其钙膜测年是特别值得进一步探索的潜在古地震研究方法或途径。     

Rockfall risk management using a pre-failure deformation database

Terrestrial laser scanning (TLS) monitoring has been used to estimate the location, volume, and kinematics of a variety of small magnitude rockfalls before failure (1–1000 m³ range), and in some cases, potential failure time has been assessed through the application of inverse velocity methods. However, our current understanding of rock slope pre-failure behavior for this magnitude range and prediction ability is based on observations of a small number of failure case histories. In this study, a pre-failure deformation database was constructed for rockfall volumes exceeding 0.1 m³, observed over a 1252-day study interval at the Goldpan rock slope, British Columbia, Canada, in order to better understand the pre-failure behavior of rock slopes and provide an empirical means of estimating temporal failure ranges. Repeated TLS datasets were acquired at an average scanning interval of 2–3 months. A total of 90 rockfall events were recorded at this site, during this time period, of which 64 (71%) exhibited measurable deformation prior to failure. Classification of rockfalls by volume suggests that a scale dependency may exist, as deformation was detected for a greater proportion of rockfalls >?5 m³ (92%) than for smaller rockfalls in the range of 0.1–0.5 m³ (61%). A lower rate of pre-failure deformation detection was also reported for planar sliding failures as compared with wedge or toppling failures, suggesting that deformation was less easily detected for these failure types. This study proposes and implements a framework for rockfall assessment and forecasting that does not require continuous monitoring of deformation.     

Application of a long-range Terrestrial Laser Scanner to a detailed rockfall study at Vall de Núria (Eastern Pyrenees, Spain)

In this study we show the application of a long-range Terrestrial Laser Scanner (TLS) to a detailed rockfall study in a test zone at Vall de Núria, located in the Eastern Pyrenees. Data acquisition was carried out using TLS-Ilris3D, the new generation of reflector-less laser scanners with a high range, accuracy and velocity of measurements. Eight scans were performed at 3 stations to acquire coordinates of almost 4 million points. The results from the acquired data are a high accuracy Digital Elevation Model (DEM) and the reconstruction of the joint geometry. The former is used for inventory of rockfalls and for more accurate rockfall simulation (trajectories and velocities). The latter allows us to model the geometry and volume of the source area in recent rockfalls. Our findings suggest that TLS technology could be a tool of reference in rockfall studies in the near future.     

Effects of sampling interval on the frequency - magnitude relationship of rockfalls detected from terrestrial laser scanning using semi-automated methods

Using change detection and semi-automated identification methods, it is possible to extract detailed rockfall information from terrestrial laser scanning data to build a database of events, which can be used in the development of the frequency-magnitude relationship for a slope. In this study, we have applied these methods to the White Canyon, a hazardous slope that presents rockfall hazards to the CN Rail line in British Columbia, to build a database of rockfalls including their locations, volumes, and block shapes. We identified over 1900 rockfall events during a 15-month period, ranging in volume from 0.01 to 45 m³. The frequency of these events changed throughout the year, with the highest periods of activity occurring over the winter months. We investigated how the sampling interval, or duration between scans, can affect how the rockfalls are identified, and therefore the frequency-magnitude relationship for the slope using datasets with fewer scans. We show that as the duration between scans becomes larger, fewer rockfalls are detected, as multiple events that have occurred in the same location cluster together into a single event. The results of this study can be used to assist the railways in planning the appropriate number and duration between future scans, in order to capture frequency-magnitude data for the slope with a desired level of detail.     

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.     

An analysis of failure mechanism constraints on pre-failure rock block deformation using TLS and roto-translation methods

Rockfall hazards increase the risk of train derailment along railway corridors in western Canada. In this study, repeated terrestrial laser scanning (TLS) datasets were collected every 2–3 months at three different sites along the Thompson and Fraser River corridors in British Columbia, referred to as the Goldpan, White Canyon, and Mile 109 sites. A total of 207 rockfall events occurring across all three sites between November 11, 2014 and October 18, 2016 were recorded in a database. For each of these rockfalls, pre-failure deformation was measured using a method of three-dimensional roto-translation block tracking. Each rockfall was classified by its deformation behaviour and further categorised based on failure mechanism, volume, lithology, and the roughness condition of the failure plane. Results reveal that detectable levels of deformation were measured in 33% of the total number of rockfall events using the present methods. Rotation deformation was most commonly observed in toppling failures with relatively steep joint orientations. Conversely, planar sliding blocks generally exhibited the least measurable deformation, with the majority not showing any precursory translation or rotation. It is postulated that overhanging rockfall configurations may suppress the expression of deformation in rockfall source blocks, though additional research is required to confirm this.     

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.     

Rockfall hazard and risk analysis for Monte da Lua,Sintra, Portugal

The prediction of rockfall trajectories below a rock cliff is essential in susceptibility, hazard and risk maps, particularity close to populated areas. The Monte da Lua hill area in Portugal, a tourist destination close to the historic city of Sintra (UNESCO World Heritage), is a typical granite boulder chaos landscape where from time to time rockfalls occur, the last such event having occurred on 29 January 2002. This area is therefore suitable to develop a rockfall study in order to provide hazard and risk maps a basis for mitigation measures. A preliminary investigation of the area leads to the identification of 188 potentially dangerous boulders. Detailed locations and geotechnical characteristics in terms of geometry, strength and context were sampled for each boulder. Digital elevations at 1 × 1 m resolution, known rockfall trajectory and building locations are provided in a GIS project for the study together with the spatial database of boulder characteristics. The modelling approach was conducted in two steps: (1) discrimination of the boulders in terms of static and dynamic mobility behaviour with multivariate analysis; (2) stochastic simulation of rockfall trajectories. The rockfall trajectory algorithm proposed is straightforward and is only dependent on elevation data, initial location of boulders and a friction angle. Due to the slope of the area, it assumes that rockfall is always of the rolling or sliding type. The friction angle was calibrated on the basis of the rockfall travel distance recorded on 29 January 2002 and generates simulated “realistic” trajectories. A smaller friction angle increases all simulated trajectories, leading to more “pessimistic” scenarios. The combined analysis of trajectories and potential damage to buildings and discrimination in terms of static and dynamic behaviour provides a final table in which all 188 sampled boulders are classified in one of the five risk grades.     

The Son Poc rockfall (Mallorca,Spain) on the 6th of March 2013: 3D simulation

The Son Poc rockfall took place on the 6th of March 2013 in the municipality of Bunyola, on the southern side of the Tramuntana Range (Mallorca) and after a rainy and cold period on the region. A volume of rock of 4.000 m³ was detached from the cliff crowning the peak falling down by toppling. The impact of the boulder caused its fragmentation, and numerous boulders bounced and rolled downslope with volumes from 1 to 35 m³, following two trajectories: southwest (SW) and southeast (SE). The SE trajectory, with a larger runout (376 m), reached an urban area, where some of the boulders hit the roofs and walls of nearby houses, stopping others in their gardening areas. Fortunately, no fatalities occurred despite of the presence of some people at that moment, but the event caused great concern in a region which lives from and for tourism. The Son Poc rockfall has been simulated using RocPro3D software which uses GIS technology to produce 3D rockfall trajectories lines, estimated velocity and energy of falling blocks, as well as bounce heights, impacts, and stopping points. The results are in agreement with field observations and with a very good accuracy between real and modeled outcomes.     

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.     

Spatio-temporal analysis of rockfall pre-failure deformation using Terrestrial LiDAR

We present a long-term spatio-temporal analysis of rock slope evolution using a Terrestrial LiDAR aiming to improve our understanding of the link between pre-failure deformation and the spatial prediction of rockfalls. We monitored the pilot study area located at the Puigcercós cliff (Catalonia, Spain) over a period of 1,705 days and detected the deformation of nine different cliff regions together with a high rockfall activity. An exact match was observed between the progressively deformed areas and the regions recently affected by three of the highest magnitude rockfall events, demonstrating a causal relationship between pre-failure deformation and rockfall occurrence. These findings allowed us to make a forward spatial prediction of future failures, hypothesizing a high probability of failure in the six remaining regions. We observed an exponential acceleration of the deformation close to failure, in accordance with tertiary creep theory. However, the temporal analysis of the deformed areas showed a complex and variable behavior, so no exact prediction of the date of failure can yet be made. Our findings have broadened our understanding of the pre-failure behavior of rockfalls and have clear implications for the future implementation of early warning systems.     

青藏铁路设兴村段崩塌特征分析与运动学模拟

西藏拉萨—羊八井段建有青藏铁路、京拉公路(G109)、京藏高速(G6)三大重要交通工程和大量输电线路。然而,该区段山高坡陡,崩塌灾害频发,给交通和输电的安全运营带来极大的威胁。现阶段对崩塌灾害的分析与预测多是基于地形剖面的二维方法,限制了崩塌块石的运动方向,难以对崩塌的影响范围进行有效的评估。鉴于此,作者借助现场调查、基于无人机航摄的高精度三维地表形貌建模、崩塌运动的三维数值模拟等方法,以青藏铁路设兴村段崩塌为例,分析了历史崩塌块石分布、岩体结构面产状和危岩区特征,并进行了崩塌块石的运动学模拟。通过模拟获得了崩塌的影响范围和到达概率、优势运动路径以及优势运动路径下危岩区块石距坡面的高度和动能,结果表明危岩区的崩塌块石主要威胁输电线路和京拉公路,对青藏铁路和京藏高速无影响。相关模拟结果还对于崩塌防护范围、高度和强度的确定具有指导意义。     

Rockfall trajectory modeling combined with heuristic analysis for assessing the rockfall hazard along the Maratea SS18 coastal road (Basilicata,Southern Italy)

In this paper, a study aimed to assess the rockfall hazard along a portion of the SS18 coastal road, located in the coastal area of Maratea (Basilicata Region, Southern Italy), is presented. The relevance of this study derives from the location of the study area, because the SS18 is a strategic roads in a touristic area, and, since the hazard assessment was performed in 2004 within a project financed by the Viability Regional Department of Autonomous National Company of Roads (ANAS), from the possibility to validate the results by using real rockfall events occurred after 2004. The procedure for assessing the rockfall hazard was composed of four sequential analyses: (i) geomechanical and kinematic characterization of rock mass, (ii) implementation of Romana’s (1985) Slope Mass Rating (SMR) method for identifying the potential boulder release areas (rockfall initiation areas), (iii) determination of rockfall trajectories by using a 3D numerical model (ROTOMAP), (iv) calculation and mapping of the hazard index by combining three factors, i.e., (a) lithological features of outcropping materials on rock faces, (b) kinematic compatibility defined by simulating the rockfall trajectories, and (c) spatial distribution of occurred rockfall events. Finally, the proposed methodology was validated by combining the distribution of the hazard levels along the road with the location on the SS18 of the rockfall events occurred from 2004 to 2014.     

Evaluation of rock falls in an urban area: the case of Boğaziçi (Erzincan/Turkey)

Disasters caused by events such as earthquake, flooding, rock falls, landslides are often encountered. However, generally, the reasons for the destructive and devastating effects of these nature events are that settlement locations were chosen without site investigation studies, or that available studies were inadequate. Such inadequacies in the field are related to inappropriate settlement location and the resulting damage caused by rock falls. This study evaluated rockfall risk in a settlement that developed in a similar manner. The study was carried out in Bo?aziçi village of Kemah (Erzincan/Turkey), which is located in a very important tectonic zone. The study site is located on the lower sections of an area with very steep cliffs and 50–75° slopes. This cliff, which is the source of rockfalls, has a slope dip of approximately 90°. The cliff comprises 25–30 m high, fractured and cracked basaltic volcanic mass. To determine block size in the study area, scanline survey measurements and block size measurements were performed on blocks that loosened and fell from the cliff face. It was found that block sizes reached 6 m³. Rockfall analyses were performed along the selected profiles using the Rockfall V.4.0 software. Kinetic energy, bounce height, horizontal location of rock end-points, and velocity of the rocks along each section were evaluated separately for each profile. This data were used to produce distribution maps for each profile and the settlement was evaluated in terms of rockfall risk. The results indicate that the study area was at risk of future rockfalls and that it would be appropriate to relocate one part of the settlement.     

郑万高铁宜万段边坡危岩崩落破坏特征

危岩是山区常见的地质灾害之一。以往研究缺少对危岩整体破坏导致危岩解体方面的关注,而危岩在失稳崩落过程中的解体行为却是预测危岩影响范围和防治成效的关键所在。为此,文章以郑万（郑州—万州）高铁宜万段沿线隧道洞口边坡危岩为研究对象,从结构面角度出发,对危岩崩落破坏特征进行研究。通过对15个隧道洞口边坡的调查,首先从边坡坡度、岩性组合、相对高差三个方面总结了研究区危岩发育分布规律;然后根据边坡岩体结构特征,分析了危岩失稳模式,并基于边坡上部危岩和下部落石的体积和形状对应关系,进一步探讨了边坡危岩崩落破坏演化过程;在此基础上,利用Rockfall模拟软件对落石运动特征进行预测分析。结果表明:（1）研究区边坡呈上陡下缓地形,上部基岩裸露,坡度基本上≥70°;危岩主要发育于弱风化的灰岩和白云岩中;边坡高差在150~300 m之间。（2）边坡上部危岩将呈阶梯状方式逐渐沿基底结构面滑移或者沿后缘结构面拉裂坠落。（3）研究区危岩崩落破坏模式主要为边坡上部岩体沿结构面解体破坏。（4）大部分隧道洞口边坡落石危险性较大,严重威胁隧道洞口的安全,需要采取相应的防治措施。研究成果可为在建的郑万高铁宜万段隧道边坡危岩的有效防治提供参考。     

Multi-scenario Rockfall Hazard Assessment Using LiDAR Data and GIS

Transportation corridors that pass through mountainous or hilly areas are prone to rockfall hazard. Rockfall incidents in such areas can cause human fatalities and damage to properties in addition to transportation interruptions. In Malaysia, the North–South Expressway is the most significant expressway that operates as the backbone of the peninsula. A portion of this expressway in Jelapang was chosen as the site of rockfall hazard assessment in multiple scenarios. Light detection and ranging techniques are indispensable in capturing high-resolution digital elevation models related to geohazard studies. An airborne laser scanner was used to create a high-density point cloud of the study area. The use of 3D rockfall process modeling in combination with geographic information system (GIS) is a beneficial tool in rockfall hazard studies. In this study, a 3D rockfall model integrated into GIS was used to derive rockfall trajectories and velocity associated with them in multiple scenarios based on a range of mechanical parameter values (coefficients of restitution and friction angle). Rockfall characteristics in terms of frequency, height, and energy were determined through raster modeling. Analytic hierarchy process (AHP) was used to compute the weight of each rockfall characteristic raster that affects rockfall hazard. A spatial model that considers rockfall characteristics was conducted to produce a rockfall hazard map. Moreover, a barrier location was proposed to eliminate rockfall hazard. As a result, rockfall trajectories and their characteristics were derived. The result of AHP shows that rockfall hazard was significantly influenced by rockfall energy and then by frequency and height. The areas at risk were delineated and the hazard percentage along the expressway was observed and demonstrated. The result also shows that with increasing mechanical parameter values, the rockfall trajectories and their characteristics, and consequently rockfall hazard, were increased. In addition, the suggested barrier effectively restrained most of the rockfall trajectories and eliminated the hazard along the expressway. This study can serve not only as a guide for a comprehensive investigation of rockfall hazard but also as a reference that decision makers can use in designing a risk mitigation method. Furthermore, this study is applicable in any rockfall study, especially in situations where mechanical parameters have no specific values.     

Magnitude and frequency relations: are there geological constraints to the rockfall size?

There exists a transition between rockfalls, large rock mass failures, and rock avalanches. The magnitude and frequency relations (M/F) of the slope failure are increasingly used to assess the hazard level. The management of the rockfall risk requires the knowledge of the frequency of the events but also defining the worst case scenario, which is the one associated to the maximum expected (credible) rockfall event. The analysis of the volume distribution of the historical rockfall events in the slopes of the Solà d’Andorra during the last 50 years shows that they can be fitted to a power law. We argue that the extrapolation of the F-M relations far beyond the historical data is not appropriate in this case. Neither geomorphological evidences of past events nor the size of the potentially unstable rock masses identified in the slope support the occurrence of the large rockfall/rock avalanche volumes predicted by the power law. We have observed that the stability of the slope at the Solà is controlled by the presence of two sets of unfavorably dipping joints (F3, F5) that act as basal sliding planes of the detachable rock masses. The area of the basal sliding planes outcropping at the rockfall scars was measured with a terrestrial laser scanner. The distribution of the areas of the basal planes may be also fitted to a power law that shows a truncation for values bigger than 50 m² and a maximum exposed surface of 200 m². The analysis of the geological structure of the rock mass at the Solà d’Andorra makes us conclude that the size of the failures is controlled by the fracture pattern and that the maximum size of the failure is constrained. Two sets of steeply dipping faults (F1 and F7) interrupt the other joint sets and prevent the formation of continuous failure surfaces (F3 and F5). We conclude that due to the structural control, large slope failures in Andorra are not randomly distributed thus confirming the findings in other mountain ranges.