Search

This paper deals with monitoring systems to manage the risk due to fast slope failures that involve rock masses, in which important elements (such as infrastructures or cultural heritages, among the others) are exposed. Three different approaches for data analysis were here compared to evaluate their suitability for detecting mutual relations among destabilising factors, acting on different time windows, and induced strain effects on rock masses: (i) an observation-based approach (OBA), (ii) a statistics-based approach (SBA) and (iii) a semi-empirical approach (SEA). For these purposes, a test-site has been realised in an abandoned quarry in Central Italy by installing a multi-parametric monitoring sensor network on a rock wall able to record strain effects induced by natural and anthropic forcing actions (like as temperature, rainfall, wind and anthropic vibrations). The comparison points out that the considered approaches allow one to identify forcing actions, responsible for the strain effects on the rock mass over several time windows, regarding a specific size (i.e., rock block dimensional scale). The OBA was more suitable for computing the relations over short- to medium time windows, as well as the role of impulsive actions (i.e., hourly to seasonal and/or instantaneous). The SBA was suitable for computing the relations over medium- to long time windows (i.e., daily to seasonal), also returning the time lag between forcing actions and induced strains using the cross-correlation statistical function. Last, the SEA was highly suitable for detecting irreversible strain effects over long- to very long-time windows (i.e., plurennial).

This paper deals with monitoring systems to manage the risk due to fast slope failures that involve rock masses, in which important elements (such as infrastructures or cultural heritages, among the others) are exposed. Three different approaches for data analysis were here compared to evaluate their suitability for detecting mutual relations among destabilising factors, acting on different time windows, and induced strain effects on rock masses: (i) an observation-based approach (OBA), (ii) a statistics-based approach (SBA) and (iii) a semi-empirical approach (SEA). For these purposes, a test-site has been realised in an abandoned quarry in Central Italy by installing a multi-parametric monitoring sensor network on a rock wall able to record strain effects induced by natural and anthropic forcing actions (like as temperature, rainfall, wind and anthropic vibrations). The comparison points out that the considered approaches allow one to identify forcing actions, responsible for the strain effects on the rock mass over several time windows, regarding a specific size (i.e., rock block dimensional scale). The OBA was more suitable for computing the relations over short- to medium time windows, as well as the role of impulsive actions (i.e., hourly to seasonal and/or instantaneous). The SBA was suitable for computing the relations over medium- to long time windows (i.e., daily to seasonal), also returning the time lag between forcing actions and induced strains using the cross-correlation statistical function. Last, the SEA was highly suitable for detecting irreversible strain effects over long- to very long-time windows (i.e., plurennial). [ABSTRACT FROM AUTHOR]

Regional and teleseismic earthquakes can induce displacements along joints in a landslideinvolved rocky slope in Central Italy. The rarity of these effects is due to specific physical properties of the seismic signals associated with: (i) the energy content, (ii) the distribution of relative energy and peak of ground acceleration related to the ground motion components and (iii) the spectral amplitude distribution in the frequency domain; these properties allow the triggering earthquakes to be distinguished from the others. The observed effects are relevant when compared to the direction of the landslide movement and the dimensions of the involved rock mass volume. The landslide movement is less constrained in the direction parallel to the dip of the slope and the landslide dimensions are associated with characteristic periods that control the landslide deformational response in relation to the spectral content of the ground motion. The earthquake-induced displacements are significant because they have the same order of magnitude as the average annual cumulative displacement based on a decade of strain measurements within the slope. [ABSTRACT FROM AUTHOR]

Ten small rock slides (with a volume ranging from 10 to 10 m) on a slope affected by working activities were detected, located, and timed using pictures collected by an automatic camera during 40 months of continuous monitoring with terrestrial SAR interferometry (TInSAR). These landslides were analyzed in detail by examining their pre-failure time series of displacement inferred from high-sampling frequency (approximately 5 min) TInSAR monitoring. In most of these cases, a typical creep behavior was observed with the displacement starting 370 to 12 h before the collapse. Additionally, an evident acceleration decrease of the displacement a few hours before the failure was observed in some rock/debris slides, thus suggesting the possibility of a mechanical feature of the slope that differs from the classical creep theory. The efficacy of the linear Fukuzono approach for the prediction of time of failure was tested by back-analyzing the ten landslides. Furthermore, a modified Fukuzono approach named average data Fukuzono (ADF) was implemented and applied to our dataset. Such an approach is able to improve forecasting effectiveness by reducing the error due to anomalies in the time series of displacement, like the acceleration decrease before failure. A prediction with a temporal accuracy of at least 2 h was obtained for all the analyzed rock/debris slides. [ABSTRACT FROM AUTHOR]

The Tyrrhenian portion of the Calabria region (southern Italy) is particularly prone to landslides as a consequence of intense morphodynamic processes. These processes affect the slopes that are composed of highly jointed metamorphic rock masses. Moreover, the frequent intense rainfalls and the up to Mw 7.0 regional earthquakes represent the main landslide triggering factors. An area of approximately $$45\,\hbox {km}^{2}$$ 45 km 2 was selected as a test site in the context of a regional project aimed at reconstructing possible earthquake-reactivated landslide scenarios (i.e., referred to already existing landslide masses). An inventory map led to the identification of 175 landslides, including rock slides, earth slides and rock falls. Ground-motion scenarios based on a spectral-matching method were derived to evaluate the expected earthquake-induced displacements of the existing landslides. Naturally recorded acceleration time histories were selected from international ground-motion databases based on a similarity index and considered representative of the seismological features of the considered seismic sources (i.e., epicentral distance, magnitude, focal mechanism). Spectral attenuation was considered, according to well-established attenuation laws, to define the expected response spectrum at the outcropping bedrock corresponding to each existing landslide. Subsequently, the selected natural records were modified to guarantee spectral matching with the attenuated response spectra at each landslide site. The derived time histories were used to compute co-seismic displacements via the classic Newmark’s sliding-block method. Different scenarios of co-seismic landslide displacements or collapse were generated for different pore-water pressure hypotheses. The strongest $$\hbox {Mw}>6$$ Mw > 6 seismic scenario (Messina Straits seismogenic source) indicated an exceedance probability of earthquake-induced co-seismic landslide collapse varying from 20 to 55 % with the increasing severity of the pore-water pressures. This probability corresponds to a percentage of co-seismic landslide displacements up to 40 % of the total inventoried landslides. The exceedance probability indicated that co-seismic landslide collapse drops below 20 % for $$\hbox {Mw}<6$$ Mw < 6 seismic scenarios. In contrast, if a uniform probability is assumed for the seismic action occurrence, i.e., return periods of 475 and 2,475 years, the total percentage of landslide co-seismic displacements could be as high as 70 and 90 %, respectively, for the considered pore-water pressures. [ABSTRACT FROM AUTHOR]

Landslides interacting with large infrastructures represent a major problem for the economy, society as a whole, and the safety of workers. Continuous monitoring for 23 months using an integrated platform with a ground-based SAR interferometer (GB-InSAR), a weather station, and an automatic camera gave us the opportunity to analyze the response of an unstable slope to the different phases of work. The deformational behavior of both the natural slope and the man-made structures was recorded and interpreted in relation to the working stages and the rainfall conditions during the whole monitoring period. A typical pattern of displacement was identified for shallow landslides, debris produced by the excavation and gabions, metallic walls, and anchored bulkheads. Furthermore, insights into the dynamics and behavior of the slope and the man-made structures that interact with the landslide were obtained. Extreme rainfall is the main trigger of shallow landslides and gabion deformations, while anchored bulkheads are less influenced by rainfalls. Movement of debris that is produced by excavations and temporary metallic barrier deformation are closely related to each other. The herein proposed monitoring platform is very efficient in monitoring unstable slopes that are affected by human activities. Moreover, the recorded patterns of displacement in the slope and the man-made structures can be used as reference data for similar studies and engineering designs. [ABSTRACT FROM AUTHOR]

Abstract: Over the last decades, time-of-failure semi-empirical prediction functions have been developed and applied to different landslides with mixed results. In this study, a field experiment was carried out to calibrate these functions with the simultaneous consideration of small-size landslides and landslides that occur on slopes modified by human activities. Four years of continuous monitoring using an integrated platform consisting of both traditional sensors (i.e., inclinometers, piezometers, load cells, topographic measurement) and innovative remote-sensing equipment (i.e., Terrestrial SAR Interferometer) resulted in the collection of a notably large amount of data. Several landslides affecting different slopes (i.e., cut slopes, cut slopes covered by spritz-beton and slopes stabilised by anchored bulkheads) were observed as part of the experiment, thus facilitating the inference of detailed information for the pre-failure behaviour. Nine landslides were back-analysed, thus allowing for calibration of the failure prediction functions for different types of slopes. From these observations, it was found that events occurring on slopes modified by human interventions could be effectively predicted using the Voight function if suitable parameters are used. As a general remark, the landslides that originate from cut slopes in natural terrain behave similar to large landslides reported in the literature (similar values of A and α) while landslides that originate from cut slopes covered by spritz beton and slopes stabilised by anchored bulkheads show α values that are significantly lower and A values that are significantly higher than those of landslides on natural terrains. [Copyright &y& Elsevier]

Abstract: On 30 January 2009, a rock slide involving approximately 0.23Mm3 of highly jointed gneiss from the local Ercinic substratum was recorded in southern Italy. The landslide occurred after exceptional autumnal rainfalls and involved a quarry whose activity has been documented over the past 10years by aerial images. An engineering-geology model of the slope involved in the landslide was developed based on the geomechanical classification of the outcropping rock masses, the ISRM (2007) indexes Ib (the block size index) and Jv (the volumetric joint count), and the observed geological setting of the slope. An equivalent continuum approach was adopted to attribute strength and stiffness parameter values to the different classes of jointed rock masses. A simplified evolutionary model of the slope was developed, starting from 300ka (i.e., from the erosional phase following the deposition of the 300-m-a.s.l. marine terrace deposits overlaying the gneiss substratum) to 30 January 2009. The model took into account the main depositional phases as indicated by the Pleistocene marine terrace deposits and the documented stages of quarry activity. Time-dependent stress–strain numerical modelling was performed by the FDM software FLAC 6.0. A visco-plastic Burger model was used to back-analyse the landslide event and to define the values of the rheological parameters for the jointed gneiss. The results, which were strongly constrained by the geomorphological evidences and by the displacement field observed before and after the landslide, demonstrated a combination of i) time-dependent gravitational slope deformation and ii) anthropogenic release due to quarry activity, which induced a progressive failure process and an increase in the jointing within the gneissic rock mass located behind the cut-wall of the quarry. Failure was ultimately triggered by intense rainfalls that occurred in the 3months before the landslide. The stress–strain numerical modelling demonstrated the reliability of visco-plastic rheology for simulating the rock mass creep in this case history: viscosity values in the range of 1019–1023 Pa·s were derived. [Copyright &y& Elsevier]