The design of remediation works for the mitigation and prevention of the associated risk is needed where these geological hazards affect anthropized areas. Remedial measures for landslides commonly include slope reshaping, plumbing, drainage, retaining structures and internal slope reinforcement, while debris flow control works consist in open or closed control structures. The effectiveness of the remedial works implemented must be assessed by evaluating the reduction of the risk over time. The choice of the most appropriate and cost-effective intervention must consider the type of hazard and environmental issues, and selects, wherever possible, naturalistic engineering operations that are consequently implemented according to the environmental regulations or the design and specification standards imposed by the competent public administrations. The mitigation procedures consist of five basic steps: (a) acquisition of the knowledge of the hazard process; (b) risk assessment with identification of possible disaster scenarios; (c) planning and designing of specific remedial measures to reduce and/or eliminate the potential risk; (d) slope monitoring after application of remedial measures, (e) transfer of knowledge to the stakeholders. This paper presents two case studies describing the practice for the design of the mitigation measures adopted for debris flow and active landslide sites in North-Eastern Italy. The first case study is a debris flow site, for which, based on observation of past events and numerical simulations using the software FLOW-2D, the most suitable mitigation measures were found to be the construction of a debris basin, barriers and breakers. The second case study deals with an active landslide threatening a village. Based on the landslide kinematics and the results of numerical simulations performed with the code FLAC, hard engineering remedial works were planned to reduce the driving forces with benching and by increasing the available resisting forces using jet grout piles and deep drainage.

We used a distributed acoustic sensing (DAS) system to monitor the evolution of debris flows in an inclined flume that was instrumented with approx. 800 m of fiber, wound in 20 coils acting as an array of coherent acoustic sensors. The analysis of the acquired signals confirmed the viability of DAS as a tool for debris flows monitoring.

The main conceptual and terminological issues related to lateral spreading are presented and accompanied by a brief outline of the state-of-the-art on the topic. Then the geomorphic features related to the two main types of spreading (rock spreading and soil spreading) are illustrated, with reference to the geological conditions in which they take place, as well as to their causes and evolution. The role of monitoring and modelling is then considered as useful tools to better understand the mechanical behavior of unstable slopes affected by such processes. Finally, some considerations on the hazard and planning implications are provided.

Debris flows are considered among the most dangerous and destructive processes that affect mountainous areas all over the world. In Italy debris flows are very common in all the Alps, and in particular in the Dolomites (North-Eastern Italy). This paper concerns the study of debris flows distribution, triggering and evolution in the Cortina d'Ampezzo area, located in the Eastern Dolomites, sample study area over about 30 years in the context of National and European research projects. The morphology of the area is characterised by sub-vertical dolomitic cliffs and a thick talus developing from their base to the valley bottom. Through the analysis of aerial photographs, 325 debris flows, both channelized and hillslope type, have been detected. They all originate at the rock cliff base and develop towards the valley floor. The morphometric and hydrologic parameters of the rock headwater catchment and of the transport and deposition zones have been measured for each debris flow, as well as the recording of the rainfall responsible for the triggering process. The debris flows have been divided according to their type (hill-slope or channelized) and rock headwater catchments which do not give rise to debris flow have been considered separately. All the collected data have been statistically analysed getting some general conclusions especially regarding the headwaters that do not originate debris flows. The mean channel lengths increase over the years, and this would seem in connection with an increasing trend of total annual rainfall and frequency of maximum intensity since the late 1980s.

This paper concerns the study of debris flows distribution, triggering, and evolution in the Cortina d'Ampezzo area, located in the Eastern Dolomites, a sample study area over about 30 years in the context of National and European research projects. Debris flows are considered among the most dangerous and destructive processes that affect mountainous areas all over the world. In Italy debris flows are very common in all the Alps, and in particular in the Dolomites (North-Eastern Italy). The morphology of the area is characterised by sub-vertical dolomitic cliffs and a thick talus developing from their base to the valley bottom. Through the analysis of aerial photos, 324 debris flows, both channelized and hillslope type, have been detected. They all originate at the rock cliff base and develop towards the valley floor. The morphometric and hydrologic parameters of the rock headwater catchment and of the transport and deposition zones have been measured for each debris flow, as well as the weather stations recording of the rainfall responsible for the triggering process. The debris flows have been divided according to their type (hillslope or channelized) and rock headwater catchments which do not give rise to debris flow have been considered separately. All the collected data have been statistically analysed getting some general conclusions especially regarding the headwaters that do not originate debris flows. The mean channel lengths increase over the years, and this would seem in connection with an increasing trend of total annual rainfall and frequency of maximum intensity since the late 1980s.

In this work, we have monitored some debris flows in an artificial inclined flume, instrumented with approx. 800 m of fiber, wound in 20 coils. The fiber was interrogated using a distributed acoustic sensing (DAS) system based on a chirped-pulses phase-sensitive optical time-domain reflectometer and the acquired signals were analyzed confirming the viability of DAS for debris flows monitoring.

Debris flows are one of the most important hazards in mountainous areas because of their paroxysmal nature, the high velocities, and energy carried by the transported material. The monitoring of these phenomena plays a relevant role in the prevention of the effects of these events. Among different possibilities, fiber optical sensors appear well-suited for this purpose thanks to their fair cheapness (with the exception of the interrogator), the robustness to electromagnetic interferences, the adaptability in extreme harsh conditions (no power supply is required), the possibility of locating the interrogator many kilometers far away from the monitored site, and the unique feature to provide very-dense multipoint distributed measurements along long distances. In this work, the vibro-acoustics signal produced by these phenomena has been focused as a possible source of information for the prediction of incipient movement, and the tracking of their path, velocity and thickness. Few literature works investigate these aspects, and for this reason, a preliminary laboratory and numerical campaign have been carried out with dry granular flume tests on an inclined chute. The discrete element method has been used to simulate the tests and to synthesize the signal measured on an instrumented mat along the channel. The grain shapes of the granular material used in simulations have been obtained by a photogrammetric tridimensional reconstruction. The force-time signal has been also analyzed in time-frequency domain in order to infer the features of the flow. The numerical activity has been preparatory for the experiments carried out by instrumenting the flume with an optical fiber distributed vibration sensing system.

One of the most important problems in designing engineering works is the knowledge of the strength parameters of the rock masses. Beside the soil-structure interaction, a satisfactory performance of structures requires that rock mass properties such as deformation modulus, intact rock and global rock mass strengths and shear strength parameters are reliably defined. The studied Calcarenite of Gravina, is a calcarenitic rock outcropping in the area of the town of Matera (Southern Italy). It is a natural soft rock, mainly used since prehistoric times as building and dimension stone, considered durable although air pollution and water weathering markedly reduce the mechanical properties both at short and long term. Consequently, locally existing cliffs may be affected by erosive phenomena and, even, by unexpected collapses resulting from complex hydro-chemo-mechanical processes. This paper presents the evaluation of the Calcarenite of Gravina physical and mechanical properties, using laboratory tests on intact rock samples collected in seven different locations. From a macroscopic point of view, calcarenites are highly porous materials showing the presence of three main components: calcareous grains, micrite matrix and sparite cement. Dry and saturated calcarenite samples have been tested according to the ISRM suggested methods at room temperature (~20°). As the studied Calcarenite cannot be considered homogenous rocks, being characterized by largely scattered pore sizes, further research on the effect of porosity on mechanical properties, mainly strength and deformability is needed and still ongoing.

Questo documento contiene alcune linee guida per il monitoraggio arginale e delle colate detritiche

Questo documento contiene i risultati preliminari della sperimentazione condotta su canaletta artificiale del sensore distribuito di vibrazione sviluppato nell'ambito del progetto DOMINO - WaterWorks2014 Cofunded Call

Debris flows are one of the most important hazards in mountainous areas because of their paroxysmal nature, the high velocities, and energy carried by the transported material. The monitoring of these phenomena plays a relevant role in the prevention of the effects of these events. Among different possibilities, fiber optical sensors appear well-suited for this purpose thanks to their fair cheapness (with the exception of the interrogator), the robustness to electromagnetic interferences, the adaptability in extreme harsh conditions (no power supply is required), the possibility of locating the interrogator many kilometers far away from the monitored site, and the unique feature to provide very-dense multipoint distributed measurements along long distances. In this work, the vibro-acoustics signal produced by these phenomena has been focused as a possible source of information for the prediction of incipient movement, and the tracking of their path, velocity and thickness. Few literature works investigate these aspects, and for this reason, a preliminary laboratory and numerical campaign have been carried out with dry granular flume tests on an inclined chute. The discrete element method has been used to simulate the tests and to synthesize the signal measured on an instrumented mat along the channel. The grain shapes of the granular material used in simulations have been obtained by a photogrammetric tridimensional reconstruction. The forcetime signal has been also analyzed in time-frequency domain in order to infer the features of the flow. The numerical activity has been preparatory for the experiments carried out by instrumenting the flume with an optical fiber distributed vibration sensing system.

Debris flows are one of the most important hazards in mountainous areas because of their paroxysmal nature, the high velocities, and energy carried by the transported material. Monitoring of these phenomena plays a relevant role in the prevention of the effects of these events. Among different possibilities, fiber optical sensors appear well-suited for this purpose thanks to their fair cheapness (with the exception of the interrogator), the robustness to electromagnetic interferences, the adaptability in extreme harsh conditions (no power supply is required), the possibility of locating the interrogator many kilometers far away from the monitored site, and the unique feature to provide very-dense multipoint distributed measurements along long distances. In this work, the vibro-acoustics signal produced by these phenomena has been focused as a possible source of information for the prediction of incipient movement, and the tracking of their path, velocity and thickness. Few literature works investigate these aspects, and for this reason, a laboratory and numerical campaign have been carried out with dry granular flume tests on an inclined chute. The discrete element method has been used to simulate the tests and to synthesize the signal measured on an instrumented mat along the channel. Different grain shapes and size obtained by a tridimensional scanning of real stones have been considered in the tests. The force-time signal has been also analyzed in time-frequency domain in order to infer the features of the flow.

The aim of this research is to deepen the knowledge of the role of friction on the dynamics of granular media; in particular the friction angle is taken into consideration as the physical parameter that drives stability, motion and deposition of a set of grains of any nature and size. The idea behind this work is a question: is the friction angle really that fundamental and obvious physical parameter which rules stability and motion of granular media as it seems from most works which deal with particle dynamics? The experimental study tries to answer this question with a series of laboratory tests, in which different natural and artificial granular materials have been investigated in dry condition by means of a tilting flume. The characteristic friction angles, both in deposition (repose) and stability limit (critical) conditions, were measured and checked against size, shape, density and roughness of the considered granular material. The flume tests have been preferred to "classical" geotechnical apparatuses (e.g. shear box) since the flume experimental conditions appear closer to the natural ones of many situations of slope stability interest (e.g. a scree slope). The results reveal that characteristic friction angles depend on size and shape of grains while mixtures of granules of different size show some sorting mechanism with less clear behaviour.

The wastes resulting from the chemical and mechanical processes of mining extraction (tailings) are mostly accumulated in basins retained by a dam that usually, after the construction of the starter dam, are raised sequentially as the impoundment fills with an upstream or downstream or centerline method. Tailing dams are particularly vulnerable to failure mainly due to: (i) poor quality of local material used for the starter dam; (ii) dam construction with solid material mixed with high quantity of water; (iii) lack of specific design criteria; (iv) lack of extensive and continuous monitoring; (v) high cost of remediation works, after the closure of mining activities. The assessment of tailings facilities has mainly concentrated on the stability of tailings dams, while relatively few studies have investigated the flow of tailings released from a dam failure due to the its complex rheological behavior. Furthermore, as many changes in the rheological values along the run-out path have been observed, different interpretations of the flow behavior exist. On July 19, 1985, a fluorite tailings dam failed at Stava, Trento, Italy. About 180,000 m3 of tailings flowed 4.2 km downstream killing 268 people and destroying 62 buildings. The tailings dams consisted of two partially overlapped basins built on a slope. The failure started at 12.22:55 with the collapse of the up-slope basin that caused the overtopping and subsequent collapse of the lower basin. The resulting slurry wave travelled along the Stava Creek reaching a speed as high as 100 km/h, until it reached the Avisio River. Different Authors [e.g.: R.J. Chandler and G. Tosatti, 1995; R. Genevois ant P.R. Tecca, 1993] concluded that the dams were constructed with an unacceptably low factor of safety and that the failure probably was triggered by a blocked decant pipe located within the tailings. In particular, the main causes of instability were found to be: (i) the under-consolidation state of the deposited material; (ii) the spreading of the upper dam on the lower basin; (iii) the excessive height and slope of the dams; (iv) the use of the upstream method, which is the cheapest, but also the most dangerous one; (v) the wrong installation of the drainage pipes. This paper, after a short history of the dams, will present a geotechnical analysis of the dam's failure and an analysis of the flow along the Stava valley.

An active debris flow seriously threatens the urbanized area of Fiames, near Cortina d'Ampezzo (Dolomites, Italy) and the National road. In September 1997, following a 25,000 m(3) magnitude debris flow that temporarily dammed the river, a retention basin with a storage capacity of about 15,000 m(3), was built upstream the National road. In 2002 a warning system was installed, based on the early detecting of debris-flow-induced ground vibrations and the overcoming of a flow-stage threshold in the debris basin, linked to a traffic light in order to stop the traffic on the National road in the event of a debris flow In the following years, after more accurated studies, more effective mitigation measures were designed. The most suitable action to reduce the risk is to control the debris deposition, because the geomorphology of the site does not allow risk mitigation measures along the flow paths. For the design of the mitigation works, the two-dimensional flow routing model FLO-2D has been used to get fundamental information such as possible runout distances, depth, velocities and impact force of the design debris flow. The magnitude of the design debris flow, based on geomorphological and historical data, has been estimated in 30,000 m(3). A debris basin and debris flow harriers and breakers have been considered the most suitable mitigation measures to protect human settlements, infrastructure and supply lines from rain-induced disasters by dissipating the energy of debris flow (floods), filtering coarse solid components and deflecting the flows from the areas at risk.

Questo rapporto descrive la modellazione numerica delle colate detritiche sviluppata nell'ambito del progetto DOMINO - WaterWorks2014 Cofunded Call

Debris flows are among the most dangerous natural hazards in mountainous areas. In European Alps, they are associated to summer heavy rainfalls and can be extremely destructive. Nevertheless, their rheology, at field scale, is still not well known. These mixtures of debris, water and air behave as non- Newtonian fluids, with a plastic yield strength, a high bulk density and a high dynamic viscosity. Indeed, these parameters are difficult to measure in the field. In this paper, data from a monitoring system are used to measure the surface velocity of debris flows, through image analysis, following the trajectories of single particles on the flow surface, and to infer shear strength and viscosity of flows. The surface velocity distribution shows at times either rigid plugs of different width or plug does not exist at all. Our observations indicate the existence of both Bingham and Newtonian behaviour even in a single surge, as the consequence of significant changes in stage, solid concentration and in particle- size. Shear strength and viscosity, can be evaluated through appropriate relationships. The analysis and processing of surface velocity distribution allow realistic estimations of crucial aspects of flow behaviour like impact forces and run-out, parameters essential for the designing of effective countermeasures.

Study about performance comparison of two numerical codes (FLO2D e IDRA2D-DF) for simulation of debris and water flows applied to a large debris-flow fan in eastern Italian Alps.

This paper presents a study of the stability of a steep rock slope, hanging over an active mine site, and a busy road. The overall assessment of the rock mass geometry and mechanical characteristics is carried out by means of both field survey and laboratory tests. The stability of the slope and its possible evolution are evaluated using the Itasca distinct element code UDEC 4.0. The results of the analyses show that heavy and prolonged rainfall is an important triggering factor for major rockfall activity. The slope instability currently concerns only blocks of relatively small size. The possibility of instability of larger rock masses or of an entire pillar cannot be ruled out, because the almost continuous rockfall activity causes a state of general instability of the entire rock mass.

This article proposes a four-staged method for a debris-flow hazard analysis which includes design volume assessment, determination of the hydrograph for predefined return periods, numerical simulations to predict the spatial distribution of deposits. A final hazard map, with the delineation of low, medium and high hazard is obtained combining the different hazard classes of the individual rheology-specific hazard maps. This hazard analysis includes both the concepts of intensity and probability of occurrence of debris flow, proving that the use of hydrological analysis implements complex forecasting methods by combining the output data obtained by numerical models.