Tommaso Carlà

Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses

Predicting the time of failure is a topic of major concern in the field of geological risk management. Several approaches, based on the analysis of displacement monitoring data, have been proposed in recent years to deal with the issue. Among these, the inverse velocity method surely demonstrated its effectiveness in anticipating the time of collapse of rock slopes displaying accelerating trends of deformation rate. However, inferring suitable linear trend lines and deducing reliable failure predictions from inverse velocity plots are processes that may be hampered by the noise present in the measurements; data smoothing is therefore a very important phase of inverse velocity analyses. In this study, different filters are tested on velocity time series from four case studies of geomechanical failure in order to improve, in retrospect, the reliability of failure predictions: Specifically, three major landslides and the collapse of an historical city wall in Italy have been examined. The effects of noise on the interpretation of inverse velocity graphs are also assessed. General guidelines to conveniently perform data smoothing, in relation to the specific characteristics of the acceleration phase, are deduced. Finally, with the aim of improving the practical use of the method and supporting the definition of emergency response plans, some standard procedures to automatically setup failure alarm levels are proposed. The thresholds which separate the alarm levels would be established without needing a long period of neither reference historical data nor calibration on past failure events.

The Calatabiano landslide (southern Italy): preliminary GB-InSAR monitoring data and remote 3D mapping

On 24 October 2015, following a period of heavy rainfall, a landslide occurred in the Calatabiano Municipality (Sicily Island, Southern Italy), causing the rupture of a water pipeline supplying water to the city of Messina. Following this event, approximately 250,000 inhabitants of the city suffered critical water shortages for several days. Consequently, on 6 November 2015, a state of emergency was declared (O.C.D.P. 295/2015) by the National Italian Department of Civil Protection (DPC). During the emergency management phase, a provisional by-pass, consisting of three 350-m long pipes passing through the landslide area, was constructed to restore water to the city. Furthermore, on 11 November 2015, a landslide remote-sensing monitoring system was installed with the following purposes: (i) analyse the landslide geomorphological and kinematic features in order to assess the residual landslide risk and (ii) support the early warning procedures needed to ensure the safety of the personnel involved in the by-pass construction and the landslide stabilization works. The monitoring system was based on the combined use of Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) and terrestrial laser scanning (TLS). In this work, the preliminary results of the monitoring activities and a remote 3D map of the landslide area are presented.

Definition of sinkhole triggers and susceptibility based on hydrogeomorphological analyses

Sinkholes represent a geological risk that is often underrated, mainly due to its very localized nature. In fact, sinkholes occur only under particular circumstances and typically affect relatively small areas. Despite these characteristics, the difficulty in forecasting the precise location and timing of their sudden collapse creates serious problems for civil protection authorities and urban planners. In this framework, identifying the mechanism and thus the triggering factor of sinkholes is strategically pivotal in developing management plans. The present paper addresses the sinkhole-prone area of Il Piano (Elba Island, Central Italy). The integration of hydrogeological surveys, coupled with a thorough study of historical maps and aerial photographs, suggests that the main triggering factor in this area may not be related to water pumping from the karst aquifer, as initially hypothesized. Instead, sinkholes appear to be caused by ravelling and erosive processes occurring entirely in the sedimentary cover when heavy rainfall induces water overpressure within the superficial aquifer.

The 10-Mile Slide and Response of a Retaining Wall to Its Continuous Deformation

Open image in new window The 10-mile Slide has a volume of about 750,000 m3 and is sliding on a through-going shear surface at velocities up to 10 mm/day. Its importance is associated with the location of a highway and a railway line within its boundaries. Risks posed to the railway were managed through monitoring and running patrols in front of trains, and a pile retaining wall was installed immediately downslope from the tracks to prevent deformations caused by loosening of materials associated with the slope deformations and delay the retrogression of the landslide. Displacement measurements of the piles have monitored the response of the wall as the landslide retrogressed upslope from the railway track. This paper presents a brief description of the 10-mile Slide geologic context, its kinematics, mechanism, and evolution followed by a presentation of measured response of the retaining wall as the landside retrogressed.

Remote 3D Mapping and GB-InSAR Monitoring of the Calatabiano Landslide (Southern Italy)

Open image in new window On October 24th 2015, following a period of heavy rainfall, a landslide triggered in the Calatabiano Municipality (Sicily Island, Southern Italy) causing the rupture of a water pipeline transect of the aqueduct supplying water to the city of Messina. This event, caused critical water shortages for several days to a large part of the city inhabitants. In order to restore the city water supplies, a provisional by-pass, consisting of three 350 m long pipes passing through the landslide area, was carried out. On November 11th 2015, a landslide monitoring system was installed, based on the combined use of advanced remote sensing techniques such as Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR), Terrestrial Laser Scanning (TLS) and Infrared Thermography (IRT). The installed monitoring system allowed to: (i) analyze the landslide geomorphological and kinematic features in order to assess the landslide residual risk; (ii) support the early warning procedures needed to ensure the safety of the personnel involved in the by-pass realization and the landslide stabilization works. In this work, the preliminary results of the monitoring activities and a 3-D mapping of the landslide area are presented.

A New Approach to Assess the Stability of Rock Slopes and Identify Impending Failure Conditions

Open image in new window Anticipating the failure of unstable slopes is a topic of major concern in the field of landslide risk management. Arbitrary displacement or velocity thresholds are typically used to setup alarms representative of different risk levels. This is a difficult process, since experience showed that failure can occur over a wide range of values of these two parameters. Other approaches, such as the well-known inverse velocity method, aim at forecasting the time of failure; however predictions can be characterized by a significant margin of error. It follows that determining when the failure of a slope is impending is still a great issue. It is therefore important to review monitoring data from past case studies and seek for recurrent correlations between specific variables in order to identify common slope behaviors in proximity of the instant of failure. The analysis of a database of rock slope failures at several coal mines is presented. For each event values of cumulative displacement and velocity measured 48 h before failure, 24 h before failure, 3 h before failure and at failure instant were provided. A straightforward correlation was found between the average acceleration during the final 3 h and the average acceleration during the final 24 h before failure, regardless of the order of magnitude of the deformation. Comparable results were obtained considering data relative to 3/48 and 24/48 h before failure. Consequently, impending failure conditions could be determined with suitable notice for future events of slope instability at the studied mine sites based on the relative intensity of the acceleration. Further development of the methodology requires that the presence of similar correlations in other databases of past slope failures is verified. The nature of the correlation may be influenced by factors such as geology, failure mechanism and mechanical properties of the rock mass.

TXT-tool 2.039-3.4 Methods to Improve the Reliability of Time of Slope Failure Predictions and to Setup Alarm Levels Based on the Inverse Velocity Method

Estimating the time of slope failure is a topic of great importance in the field of landslide risk mitigation. Within this framework, time of failure forecasting methods based on the inverse velocity, typically intended as the extrapolation of linear trend lines of the inverse of velocity with time, are widely known as tools for early warning of slopes displaying accelerating trends of deformation rate. Although nominally simple, their correct application is actually tricky as many factors can influence displacement data and eventually heavily reduce the accuracy of the predictions. Such disturbing elements can be classified as noise caused by instrumental precision and as noise representing the diverging of a natural behavior with respect to an ideal inverse velocity trend. Hence correctly preparing the dataset is a pivotal and critical task. The present teaching tool describes how to filter displacement data by presenting three different approaches and discussing the results of their application to three large slope failure case histories in Italy, in order to improve, in retrospect, the reliability of the failure-time predictions. Procedures to automatically setup alarm levels of slope failure occurrence are consequently proposed for supporting the definition of landslide emergency response plans.

Reply to discussion on “Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses” by F. Bozzano, P. Mazzanti, and S. Moretto

Abstract■■■The paper “Discussion to: Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses by T. Carlà, E. Intrieri, F. Di Traglia, T. Nolesini, G. Gigli and N. Casagli” by Bozzano et al. brings forward new considerations on an issue of extreme concern in landslide risk management. To this day, the ability to predict catastrophic landslide failures from slope surface displacements is a problem dictated more by practical constraints rather than by theoretical uncertainties. In this sense, the development of data interpretation practices is crucial. This short reply provides a few further insights with regard to this subject, also in the context of the recently published literature.