Ultimate lateral pressures exerted on buried pipelines by the initiation of submarine landslides

Submarine slope instabilities are considered one of the major threats for offshore buried pipelines. This paper presents a novel method to evaluate the ultimate pressure acting on a buried pipeline during the liquefaction of an inclined seabed. Small-scale model tests with pipes buried at three different embedment ratios have been conducted at an enhanced centrifugal acceleration condition. A high-speed, high-resolution imaging system was developed to quantify the soil displacement field of the soil body and to visualize the development of the liquefied zone. The measured lateral pressures were compared with the hybrid approach proposed for the landslide–pipeline interaction in clay-rich material by Randolph and White (2012) and Sahdi et al. (2014). The hybrid approach is proved to be able to predict later pressures induced by the movement of (partially) liquefied sand on buried pipelines. It is found that the fluid inertia (fluid dynamics) component plays an important role when the non-Newtonian Reynolds number >~2 or the shear strain rate > 4.5 × 10−2 sec−1.

Active landslides in the Rogun Catchment, Tajikistan, and their river damming hazard potential

The region of Tajikistan where the Rogun Hydropower Project is currently under construction has experienced large and catastrophic slope failures in the past, often triggered by earthquakes. Co-seismic slope failures are thus common and pose a high hazard potential; however, to date, no specific analysis of slope activity in this area has been presented in international journals. Here, we present an inventory of active landslides identified through satellite imagery analysis and in particular by exploiting space-borne differential radar interferometry. Surface displacements provide the basis for the detection of active slope instabilities, which are then further classified by using geomorphological indicators visible in optical satellite imagery. Additionally, the proximity of active landslides to tectonic lineaments, as well as regional seismicity, is analysed to investigate potential relationships and to provide an integrated river damming hazard potential. The results show that approximately 31% of all detected landslides would have a high damming hazard potential upon catastrophic failure, highlighting the importance of such phenomena for efficient long-term land use planning and management of hydropower plants.

Offshore Geological Hazards: Charting the Course of Progress and Future Directions

Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most common hazardous processes; tsunamis are also examined because they are a secondary hazard generated mostly by earthquakes, slope instabilities, or volcanic eruptions. The hazards can co-occur and interact, inducing a cascading sequence of events, especially in certain contexts, such as tectonic indentations, volcanic islands, and canyon heads close to the coast. We analyze the key characteristics and main shortcomings of offshore geological hazards to identify their present and future directions for marine geoscience investigations of their identification and characterization. This review establishes that future research will rely on studies including a high level of multidisciplinarity. This approach, which also involves scientific and technological challenges, will require effective integration and interplay between multiscale analysis, mapping, direct deep-sea observations and testing, modelling, and linking offshore observations with onshore observations.

A device for rainfall simulation in geotechnical centrifuges

Rainfall-induced slope instabilities are ubiquitous in nature, but simulation of this type of hazards with centrifuge modelling still poses difficulties. In this paper, we introduce a rainfall device for initiating slope failure in a medium-sized centrifuge. This rainfall system is simple, robust and affordable. An array of perforated hoses is placed close above the model slope surface to generate the raindrops. The rainfall intensity depends on the centrifuge acceleration and the flow rate of the water supply, which is controlled by the size and number of the tiny pinholes in the hose walls. The rainfall intensities that are tested range from 2.5–30 mm/h, covering the intensity range of moderate, heavy and torrential rainfall events. Our model test with rainfall-induced slope failure shows that this system is capable of generating relatively uniform rainfall of wide intensities and leads to various patterns of slope failure.

A new rating system for hydrogeological risk management along railway infrastructures in Prealpine zone (northern Italy)

Railway infrastructures in mountain areas often develop along hillslopes affected by geomorphological and hydrogeological processes which might lead hazardous events. Therefore, specific tools for risk analysis and management are required. This paper develops a new rating system (Railway Hydrogeological Management System, RHMS), based on a heuristic method which considers the susceptibility to different types of slope instabilities, as well as the peculiar features affecting the railway vulnerability. The proposed method introduces an iterative approach for the risk assessment, based on the definition of acceptability thresholds for the residual risk. The application of this method to a test area pointed out its feasibility, as well as its operational capability to identify the critical sections of the infrastructure, in which protection or mitigation measures are needed in order to reduce the risk.

Relationships between Morphostructural/Geological Framework and Landslide Types: Historical Landslides in the Hilly Piedmont Area of Abruzzo Region (Central Italy)

Landslides are a widespread natural phenomenon that play an important role in landscape evolution and are responsible for several casualties and damages. The Abruzzo Region (Central Italy) is largely affected by different types of landslides from mountainous to coastal areas. In particular, the hilly piedmont area is characterized by active geomorphological processes, mostly represented by slope instabilities related to mechanisms and factors that control their evolution in different physiographic and geological–structural conditions. This paper focuses on the detailed analysis of three selected case studies to highlight the multitemporal geomorphological evolution of landslide phenomena. An analysis of historical landslides was performed through an integrated approach combining literature data and landslide inventory analysis, relationships between landslide types and lithological units, detailed photogeological analysis, and geomorphological field mapping. This analysis highlights the role of morphostructural features on landslide occurrence and distribution and their interplay with the geomorphological evolution. This work gives a contribution to the location, abundance, activity, and frequency of landslides for the understanding of the spatial interrelationship of landslide types, morphostructural setting, and climate regime in the study area. Finally, it represents a scientific tool in geomorphological studies for landslide hazard assessment at different spatial scales, readily available to interested stakeholders to support sustainable territorial planning.

Monitoring Rock Slope Instabilities Using Frequency Domain Decomposition Modal Analysis

<p>Measuring ambient seismic vibration provides a promising tool to monitor unstable rock slopes due to its independence from actual surface deformations. It is generally observed that the seismic wavefield, arising from ambient vibrations, polarizes perpendicular to open fractures and that unstable slopes exhibit strong wavefield amplifications compared to stable reference sites. Rock slope instabilities dominated by deep persistent fracture sets exhibit normal mode behaviour due to standing wave phenomena within individual compartments of the unstable volume. Techniques to assess such behavior are well established in mechanical and civil engineering to assess the dynamic response and possibly the structural integrity of the structure studied.</p><p> </p><p>We performed enhanced frequency domain decomposition modal analysis on ambient vibration data acquired in real-time on an unstable rock site with a volume larger than 150,000 m<sup>3</sup> near Preonzo, Switzerland. We tracked the resonance frequency and normal mode polarization of the first two modes over a period of four years. In addition, we show the development of the modal damping ratio of the fundental mode over time, which is a measure of energy dissipation within and out of the system. We found that the dynamic properties of the rock structure experienced annual variations and that they are primarily controlled by temperature and only secondarily by the exension and closure of large-scale fractures. Even though no large slope failure was observed during the monitoring period, the dataset provides a reference model for ongoing slope monitoring, as the resonance frequency and damping ratio is expected to change significantly prior to failure.</p>

Distributed modeling of runoff and soil erosion in vegetated slopes with man-made mountain tracks

<p>Mountain tracks and slope cuts are important sources of runoff and sediment transport in a watershed. Some slope instabilities are also observed nearby mountain roads and tracks. Most of the current literature points out as relevant the modifications of the slope topography, and the concentration of runoff at the bends of the trackways. However, quantitative analysis of runoff generation and sediment delivery are still uncommon. Moreover, the role of vegetation removal or modification along/nearby tracks is not addressed. A physically-based distributed modelling of water runoff, soil erosion and deposition on a natural slope is performed considering the impacts of a mountain track, either in terms slope topography modifications or for the infiltration-runoff patterns. The erosion scenarios for a 30° steep slope are computed with different rainstorms and initial soil suction considered. The numerical analyses provide a comprehensive set of erosion scenarios. Particularly, the numerical results outline the bend of the mountain roads as a major confluence path for water runoff, consistently with the in-situ evidences. The highest loss of soil is found besides and downslope the bends. Very unfavorable combinations of vegetation removal and change in slope topography may finally lead to extensive rill erosions and/or shallow slope failures.</p>

Ground motion detection in Central South Asturias (N Spain) by using Sentinel-1 SAR data

<p>In this work, the A-DInSAR techniques are applied in a mountainous area located in the Central South of Asturias (N Spain), where there are significant landslide and subsidence phenomena. The main aim of this study is detecting and analysing ground deformations associated to slope instabilities and subsidence processes. For this, 113 SAR images, provided by Sentinel-1A/B between January 2018 and February 2020, were acquired and processed by means of PSIG software (developed by the Geomatics Division of the CTTC). The results show a velocity range between -18.4 and 10.0 mm/year, and minimum and maximum accumulated ground displacements of -35.0 and 17.5 mm. This study has made possible to differentiate local sectors with recent deformation related to landslide incidence, urban/mining subsidence, and land recuperation due to aquifer recharge. This work corroborates the reliability and usefulness of the A-DInSAR processing as a powerful tool in the study and analysis of geological hazards on regional and local scales using Sentinel-1 data collection, showing also the high difficulty of processing mountainous areas with few urban sectors.</p>