Assessment of rockfall risk along roads

International audienceThis paper contains a method for the analysis of rockfall risk along roads and motorways. The method is derived from the Rockfall Hazard Rating System (RHRS) developed by Pierson et al. (1990) at the Oregon State Highway Division. The RHRS provides a rational way to make informed decisions on where and how to spend construction funds. Exponential scoring functions are used to represent the increases, respectively, in hazard and in vulnerability that are reflected in the nine categories forming the classification. The resulting total score contains the essential elements regarding the evaluation of the degree of the exposition to the risk along roads. In the modified method, the ratings for the categories "ditch effectiveness", "geologic characteristic", "volume of rockfall/block size", "climate and water circulation" and "rockfall history" have been rendered more easy and objective. The main modifications regard the introduction of Slope Mass Rating by Romana (1985, 1988, 1991) improving the estimate of the geologic characteristics, of the volume of the potentially unstable blocks and the underground water circulation. Other modifications regard the scoring for the categories "decision sight distance" and "road geometry". For these categories, the Italian National Council's standards (Consiglio Nazionale delle Ricerche - CNR) have been used (CNR, 1980). The method must be applied in both the traffic directions because the percentage of reduction in the decision sight distance greatly affects the results. An application of the modified method to a 2km long section of the Sorrentine road (no 145) in Southern Italy was developed. A high traffic intensity affects the entire section of the road and rockfalls periodically cause casualties, as well as a large amount of damage and traffic interruptions. The method was applied to seven cross sections of slopes adjacent to the Sorrentine road. For these slopes, the analysis shows that the risk is unacceptable and it should be reduced using urgent remedial works

Comparison between qualitative rockfall risk rating systems for a road affected by high traffic intensity

Abstract. The paper deals with the assessment of the rockfall risk for a road stretch, in southern Italy, affected by high traffic intensity. Three qualitative rockfall risk rating systems (QRSs) which use an exponential scoring with a base of 3 were employed, and then the results were compared. The used methods are the following: the Rockfall Hazard Rating System, a modified version of this method already proposed in the past by one of the authors, and the modified version of the Colorado Rockfall Hazard Rating System. The studied road stretch is about 11 km in length and is part of a very tortuous road flanked by rock slopes characterised by complex geostructural and geomechanical layouts. The road was subdivided into 56 sections, defined so as to have – as much as possible – homogeneous geological characteristics. By means of the three QRSs, it was possible to ascertain that high levels of rockfall risks are due to the lack of ditches, a very limited percentage of decision sight distance (PDSD) values and a small roadway width, whereas a subordinate factor is the hazard caused by rockfalls. Several positive and negative aspects arising from the use of the employed methods are highlighted and discussed.</p

Experimentation of two coupled gravity meters in continuous recording with a high sampling rate at Etna volcano

During the summer of 2005, we performed a 2-month lasting experiment (29 July - 29 September), using two spring gravimeters installed side-by-side at Mt. Etna. Two LaCoste & Romberg gravimeters were utilized (G594 and G1190), each equipped with an Aliod 100 electronic feedback system. Data were acquired at a sampling rate (2 Hz) higher than that normally used for gravimetric recordings. Apparent fluctuations (i.e. instrumental, not due to actual changes of the gravity field) dominated by a component with period of about 20 seconds appear over the gravity recordings when both high-frequency (local earthquakes) and low-frequency (teleseisms) components dominate the ensuing seismic wavefield. Though it has only an instrumental character, the outcome of this study represent an important further step towards the development of any a-priori or a-posteriori system aimed at reduce the effect of seismic shocks on the signal from continuously recording gravimeters

Extended Glasgow Outcome Scale to Evaluate the Functional Impairment of Patients With Subcortical Band Heterotopia: A Multicentric Cross-sectional Study

Background: Subcortical band heterotopia (SBH) is a rare malformation of the cortical development characterized by a heterotopic band of gray matter between cortex and ventricles. The clinical presentation typically includes intellectual disability and epilepsy. Purpose: To evaluate if the Extended Glasgow Outcome Scale-pediatric version (EGOS-ped) is a feasible tool for evaluating the functional disability of patients with (SBH). Method: Cross-sectional multicenter study of a cohort of 49 patients with SBH (female n = 30, 61%), recruited from 23 Italian centers. Results: Thirty-nine of 49 (80%) cases showed high functional disability at EGOS-ped assessment. In the poor result subgroup (EGOS-ped &gt;3) motor deficit, language impairment, and lower intelligence quotient were more frequent (P &lt; 0.001, P = 0.02, and P = 0.01, respectively); the age at epilepsy onset was remarkably lower (P &lt; 0.001); and the prevalence of epileptic encephalopathy (West syndrome or Lennox-Gastaut-like encephalopathy) was higher (P = 0.04). The thickness and the extension of the heterotopic band were associated with EGOS-ped score (P &lt; 0.01 and P = 0.02). Pachygyria was found exclusively among patients with poor outcome (P &lt; 0.01). Conclusions: The EGOS-ped proved to be a reliable tool for stratifying the functional disability of patients with SBH. According to this score, patients could be dichotomized: group 1 (80%) is characterized by a poor overall functionality with early epilepsy onset, thick heterotopic band, and pachygyria, whereas group 2 (20%) is characterized by a good overall functionality with later epilepsy onset and thinner heterotopic band

Continuous dynamic response along a pre-existing structural discontinuity induced by the 2001 eruption at Mt. Etna

The intrusive process of the 2001 Mt. Etna eruption was accompanied by marked ground deformation and relevant seismic activity recorded between 12 and 17 of July (INGV-CT, 2001). At the same time, extensometer data evidenced the re-activation of a dry surface failure zone on the high south-eastern sector of Mt. Etna; this fracture system, formed in 1989, has been related to the propagation of a shallow blade-like dike along a NNESSW discontinuity (Bonaccorso and Davis, 1993; Bianco et al., 1998). The NNW-SSE discontinuity represents a complex low cohesion structure in which deformation may concentrate. Displacement measurements recorded on the surface fracture and the constraints obtained from seismicity show that the intrusion phase of the 2001 eruption has forced the NNE-SSW structure to move continuously with prevalent left-lateral displacement from a depth of 2–2.5 km b. s. l. to the surface with a compositive slip of about 3–5 centimeters.Published56/ (2004)ope

Recommendations for the quantitative analysis of landslide risk

This paper presents recommended methodologies for the quantitative analysis of landslide hazard, vulnerability and risk at different spatial scales (site-specific, local, regional and national), as well as for the verification and validation of the results. The methodologies described focus on the evaluation of the probabilities of occurrence of different landslide types with certain characteristics. Methods used to determine the spatial distribution of landslide intensity, the characterisation of the elements at risk, the assessment of the potential degree of damage and the quantification of the vulnerability of the elements at risk, and those used to perform the quantitative risk analysis are also described. The paper is intended for use by scientists and practising engineers, geologists and other landslide experts

Rockfall-induced impact force causing a debris flow on a volcanoclastic soil slope: a case study in southern Italy

On 10 January 2003, a rockfall of approximately 10m3 affected a cliff some 25mhigh located along the northern slopes of Mt. St. Angelo (Nocera Inferiore, province of Salerno) in the southern Italian region of Campania. The impact of boulders on the lower sector of the slope, along which detrital-pyroclastic soils outcrop, triggered a small channelled debris flow of about 500m3. Fortunately, no damage nor victims resulted from the landslide. Several marks of the impacts were observed at the cliff toe and outside the collapsed area, and the volumes of some fallen boulders were subsequently measured. By means of in-situ surveys, it was possible to reconstruct the cliff’s geo-structural layout in detail. A rockfall back-analysis was subsequently performed along seven critical profiles of the entire slope (surface area of about 4000m2). The results of this numerical modelling using the lumped-mass method were then used to map the kinetic iso-energy curves. In the triggering area of the debris flow, for a falling boulder of 1m3, the mean kinetic energy was estimated at 120 kJ, this value being equivalent to an impact force, on an inclined surface, of some 800 kN. After landing, due to the locally high slope gradient (about 45), and low angle of trajectory at impact (about 23), some boulders slid down the slope as far as the endpoints. The maximum depth of penetration into the ground by a sliding block was estimated at about 16 cm. Very likely, owing to the high impact force of boulders on the saturated soil slope outcropping at the cliff base, the debris flow was triggered under undrained loading conditions. Initial failure was characterized by a translational slide involving a limited, almost elliptical area where the pyroclastic cover shows greater thickness in comparison with the surrounding areas

Landslide hazard assessment of the Cilento rocky coasts (Southern Italy)

This paper deals with natural and human causes giving rise to the erosion of the Cilento rocky coasts. It is predictable that, in 2100, along the coasts of the Mediterranean Sea a sea level rise varying between 9 and 30 cm will be attained. This increase will also cause a marked rise in the erosion of rocky coasts because a wide extension of highly erodible rock masses characterizes the studied area. Data regarding failure mechanisms, landslide mobility as well as run out distances of about 228 landslides directly or indirectly triggered by the wave motion were collected. Using these data and the IFFI Catalogue (“Inventario Fenomeni Franosi Italiani”), a Coastal Landslide Density Map was drawn that displays landslide density areas varying between 2 and 10 landslides per km2. In addition to climatic, geomorphological and geological causes, coastal erosion is worsened by a poor supply of sediments providing beaches, coming from the nine main rivers of the area. Furthermore, these sediments show a granulometric sorting mainly towards fine sands and silts which are not suitable for the beach-nourishment. In order to obtain a relative estimate of net erosion and deposition along the bed rivers, the USPED (Unit Stream Power - based Erosion Deposition) model was applied that allowed to calculate a value of solid discharge, from the rivers of the area, of about 11 millions of T/year. An assessment of the potential degree of landslide hazard and rockfall mobility was performed by means of heuristic approaches based on the “Rock Engineering System” and “Reach Probability” methods. In spite of inevitable approximations, employed methods revealed that almost 56% of the coastal area displays high landslide hazard, 27% is characterized by medium landslide hazard, whereas only 17% is characterized by low landslide hazard