Impact Forces and Energy of Flow-like Landslides Against Protection Barriers: a New MPM-validated Empirical Formulation

Full understanding the interaction mechanisms between flow-like landslides and the impacted protection structures is an open issue. In fact, while researchers have used several approaches, from experimental to numerical, it is true that the adequate assessment of the hydromechanical behaviour of the landslide body requires both a multiphase and large deformation approach.This paper firstly proposes a conceptual framework for a specific type of protection structure, namely a rigid barrier fixed to the base ground. Two different approaches are proposed: i) an advanced hydro-mechanical numerical model based on Material Point Method is tested in simulating the whole complex landslide-structure-interaction mechanism(s), ii) a more simplified empirical model is casted to estimate the impact force and the time evolution of kinetic energy. The calibration and validation of the empirical formulation are pursued, respectively, based on the MPM numerical results, and referring to a large dataset of field evidence for the peak impact pressure. Finally, the performance of the newly proposed empirical method is compared to the methods available in the literature and its advantages are outlined.

Multi-Level Sensing Technologies in Landslide Research—Hrvatska Kostajnica Case Study, Croatia

In March 2018, a landslide in Hrvatska Kostajnica completely destroyed multiple households. The damage was extensive, and lives were endangered. The question remains: Can it happen again? To enhance the knowledge and understanding of the soil and rock behaviour before, during, and after this geo-hazard event, multi-level sensing technologies in landslide research were applied. Day after the event field mapping and unmanned aerial vehicle (UAV) data were collected with the inspection of available orthophoto and “geo” data. For the landslide, a new geological column was developed with mineralogical and geochemical analyses. The application of differential interferometric synthetic aperture radar (DInSAR) for detecting ground surface displacement was undertaken in order to determine pre-failure behaviour and to give indications about post-failure deformations. In 2020, electrical resistivity tomography (ERT) in the landslide body was undertaken to determine the depth of the landslide surface, and in 2021 ERT measurements in the vicinity of the landslide area were performed to obtain undisturbed material properties. Moreover, in 2021, detailed light detection and ranging (LIDAR) data were acquired for the area. All these different level data sets are being analyzed in order to develop a reliable landslide model as a first step towards answering the aforementioned question. Based on applied multi-level sensing technologies and acquired data, the landslide model is taking shape. However, further detailed research is still recommended.

Prediction of Slow-Moving Landslide Mobility Due to Rainfall Using a Two-Wedges Model

In the present study, the landslides cyclically reactivated by water-table oscillations due to rainfall are dealt with. The principal kind of motion that usually characterizes such landslides is a slide with rather small velocity. As another feature, soil deformations are substantially accumulated inside a narrow shear zone situated below the landslide body so that the latter approximately slides rigidly. Within this framework, a new approach is developed in this paper to predict the mobility of this type of landslides due to rainfall. To this end, a two-wedges model is used to schematize the moving soil mass. Some analytical solutions are derived to link rain recordings with water-table fluctuations and in turn to landslide displacements. A well-documented landslide frequently activated by rainfall is studied to check the forecasting capacity of the proposed method.

A Large Old Landslide in Sichuan Province, China: Surface Displacement Monitoring and Potential Instability Assessment

Using advanced Differential Interferometric Synthetic Aperture Radar (InSAR) with small baseline subsets (SBAS) and Permanent Scatter Interferometry (PSI) techniques and C-band Sentinel-1A data, this research monitored the surface displacement of a large old landslide at Xuecheng town, Lixian County, Sichuan Province, China. Based on the MassMov2D model, the effect of the dynamic process and deposit thickness of the potentially unstable rock mass (deformation rate < −70 mm/year) on this landslide body were numerically simulated. Combined with terrain data and images generated by an Unmanned Aerial Vehicle (UAV), the driving factors of this old landslide were analyzed. The InSAR results show that the motion rate in the middle part of the landslide body is the largest, with a range of −55 to −80 mm/year on average, whereas those of the upper part and toe area were small, with a range of −5 to −20 mm/year. Our research suggests that there is a correlation between the LOS (line of sight) deformation rate and rainfall. In rainy seasons, particularly from May to July, the deformation rate is relatively high. In addition, the analysis suggests that SBAS can provide smoother displacement time series, even in areas with vegetation and the steepest sectors of the landslide. The simulation results show that the unstable rock mass may collapse and form a barrier dam with a maximum thickness of about 16 m at the Zagunao river in the future. This study demonstrates that combining temporal UAV measurements and InSAR techniques from Sentinel-1A SAR data allows early recognition and deformation monitoring of old landslide reactivation in complex mountainous areas. In addition, the information provided by InSAR can increase understanding of the deformation process of old landslides in this area, which would enhance urban safety and assist in disaster mitigation.

Biogeochemical assessment of changes in water composition after a large landslide in winter

Впервые в декабре 2018 г. при температуре –32 оС произошел оползень с крутого берега Бурейского водохранилища (Дальний Восток России), на водосборе которого встречаются островная, прерывистая и сплошная многолетняя мерзлота. Оползень общим объемом 24.5 млн. м3 полностью перекрыл бывшее русло реки Бурея, создав угрозу работе Бурейской ГЭС и затопления населенных пунктов. Для решения проблемы восстановления проточности были проведены крупномасштабные взрывные работы с использованием тротила, а также кумулятивных зарядов с гексогеном. Взрывные работы повлияли на спектр органических веществ и миграционную способность многих элементов в воде вокруг оползня. Методом газовой хроматографии в воде обнаружены метанол и метилированные производные бензола, их концентрация увеличивалась после дренажа воды сквозь тело оползня. Среди летучих органических веществ значительную долю составляли продукты трансформации высокомолекулярных природных соединений, которые принимают участие в процессах метаногенеза и метанотрофии (метанол, ацетаты, ксилолы) и толуол, основной продукт деструкции тротила. Исследования элементного состава воды в зоне влияния оползня до и после проведения взрывных работ были проведены методом масс-спектрометрии с индуктивно связанной плазмой на ICP-MS ELAN-9000 (Perkin Elmer). Ниже тела оползня отмечено увеличение содержания Al, Fe, W, Cr и Pb. Наиболее существенные изменения качества воды произошли после проведения взрывных работ. В воде искусственного канала отмечено резкое снижение содержания элементов (Fe, Cu, Zn и Pb) и увеличение концентрации ртути. For the first time in December 2018, at a temperature of 32°C below zero, on the steep bank of the Bureiskoe Reservoir (Far East, Russia) a landslide occurred. Insular, discontinuous, and continuous permafrost on the catchment basin of the reservoir is recorded. A landslide with a total volume of 24.5 million m3 completely blocked the former channel of the Bureya River. It created a threat to the operation of the Bureya Hydro-electric Power Station and flooding of settlements. Blasting operations with use of trinitrotoluene and shaped charges with hexogen were carried out for restoring the flow. Methanol and methylated benzene derivatives were detected in water by gas chromatography; its concentration increased after the water was drained through the landslide body. In the water of the artificial channel, decrease in the lithogenic elements (Fe, Cu, Zn, and Pb) content and an increase in the mercury concentration were recorded. Among the volatile organic substances, a significant portion belonged to the products of transformation of high molecular natural compounds that take part in the processes of methanogenesis and methanotrophy (methanol, acetates, and xylenes) and toluene, the main intermediate of trinitrotoluene. The studies of the elemental composition of water in the zone of influence of the landslide before and after the blasting operations were carried out by inductively coupled plasma mass spectrometry on an ICP-MS ELAN-9000 (Perkin Elmer). Below the landslide body, an increase in the content of Al, Fe, W, Cr and Pb is noted. The most significant changes in water quality occurred after the blasting operations. In the water of the artificial channel, a sharp decrease in the content of elements (Fe, Cu, Zn and Pb) and an increase in the concentration of mercury have been recorded.

Experimental Study on Landslides of Loose Sediment Slope Induced by Stream Bed Incision

Uplift of the Qinghai-Tibetan Plateau has resulted in rapid incision of rivers along the margin of the plateau. Landslides occur frequently as a consequence of increasing bank slope and potential landslide energy due to stream bed incision or lateral bank erosion on the concave banks at bends. The Fencha Gully is on the eastern margin of the Qinghai-Tibetan Plateau and is developing on a huge landslide body. Flume experiments were conducted on the base of the field investigation to study the mechanism of landslides induced by stream bed incision. The experiments were designed with a length scale ratio of 1:20. Landslides and stream bed incision with loose sediment were observed and analyzed. The results show that landslides are induced as a result of stream bed incision. The potential landslide energy is defined, which increases quickly with an effective incision depth coupling vertical incision and lateral bank erosion. The occurrence of landslides can be attributed to increasing incision depth and potential landslide energy. Results indicate that the critical effective incision depth is 4.0–6.0 m. A critical value of the potential landslide energy is found from the experiments. Landslides occur if the potential energy exceeds the critical energy, which is 2.24×104 t·m/s2 for the Fencha Gully. The incision depth and potential energy of landslides from the Fencha Gully agree well with the results.

Change in Abundance and Activity of Microbocenoses in the Area of Influence of a Large Landslide at the Bureya Reservoir

The results of field and experimental microbiological studies of water, soil, and rock samples in the influence zone of large landslide are presented. The landslide occurred in December 2018 and blocked the Bureya Reservoir from coast to coast. An artificial channel was created to restore the hydrological regime with the use of TNT (trinitrotoluene) and RDX (hexogen). A comparative analysis of the abundance of cultivated heterotrophic bacteria around the landslide body and in the artificial channel is carried out. The activity of microbial communities in relation to easily available (peptone, lactate, and starch) and difficult-to-mineralize humic compounds is also determined. With the use of spectrometry and gas chromatography, it is shown that an increase in the diversity of aromatic compounds in water is accompanied by an increase in the abundance of heterotrophic bacteria. A number of toxic substances, including methanol and methylated benzene derivatives, are found among the dominant components in the water. Its concentrations increased after the water drained through the landslide body and after imploding works. Many of the volatile organic compounds may have been products of microbial metabolism when water interacts with rocks. A hypothesis on the role of methanotrophic and methylotrophic bacteria in the genesis of methanol and toluene is discussed.

Landslide geometry and activity in Villa de la Independencia (Bolivia) revealed by InSAR and seismic noise measurements

Interferometric Synthetic Aperture Radar (InSAR) enables detailed investigation of surface landslide movements, but it cannot provide information about subsurface structures. In this work, InSAR measurements were integrated with seismic noise in situ measurements to analyse both the surface and subsurface characteristics of a complex slow-moving landslide exhibiting multiple failure surfaces. The landslide body involves a town of around 6000 inhabitants, Villa de la Independencia (Bolivia), where extensive damages to buildings have been observed. To investigate the spatial-temporal characteristics of the landslide motion, Sentinel-1 displacement time series from October 2014 to December 2019 were produced. A new geometric inversion method is proposed to determine the best-fit sliding direction and inclination of the landslide. Our results indicate that the landslide is featured by a compound movement where three different blocks slide. This is further evidenced by seismic noise measurements which identified that the different dynamic characteristics of the three sub-blocks were possibly due to the different properties of shallow and deep slip surfaces. Determination of the slip surface depths allows for estimating the overall landslide volume (9.18 · 107 m3). Furthermore, Sentinel-1 time series show that the landslide movements manifest substantial accelerations in early 2018 and 2019, coinciding with increased precipitations in the late rainy season which are identified as the most likely triggers of the observed accelerations. This study showcases the potential of integrating InSAR and seismic noise techniques to understand the landslide mechanism from ground to subsurface.

Development of smart boulders to monitor mass movements via the Internet of Things: a pilot study in Nepal

Boulder movement can be observed not only in rockfall activity, but also in association with other landslide types such as rockslides, soil slides in colluvium originating from previous rockslides, and debris flows. Large boulders pose a direct threat to life and key infrastructure in terms of amplifying landslide and flood hazards as they move from the slopes to the river network. Despite the hazard they pose, boulders have not been directly targeted as a mean to detect landslide movement or used in dedicated early warning systems. We use an innovative monitoring system to observe boulder movement occurring in different geomorphological settings before reaching the river system. Our study focuses on an area in the upper Bhote Koshi catchment northeast of Kathmandu, where the Araniko highway is subjected to periodic landsliding and floods during the monsoons and was heavily affected by coseismic landslides during the 2015 Gorkha earthquake. In the area, damage by boulders to properties, roads, and other key infrastructure, such as hydropower plants, is observed every year. We embedded trackers in 23 boulders spread between a landslide body and two debris flow channels before the monsoon season of 2019. The trackers, equipped with accelerometers, can detect small angular changes in the orientation of boulders and large forces acting on them. The data can be transmitted in real time via a long-range wide-area network (LoRaWAN®) gateway to a server. Nine of the tagged boulders registered patterns in the accelerometer data compatible with downslope movements. Of these, six lying within the landslide body show small angular changes, indicating a reactivation during the rainfall period and a movement of the landslide mass. Three boulders located in a debris flow channel show sharp changes in orientation, likely corresponding to larger free movements and sudden rotations. This study highlights the fact that this innovative, cost-effective technology can be used to monitor boulders in hazard-prone sites by identifying the onset of potentially hazardous movement in real time and may thus establish the basis for early warning systems, particularly in developing countries where expensive hazard mitigation strategies may be unfeasible.

Monitoring and analysis of Woda landslide stability (China) combined with InSAR, GNSS and meteorological data

Detecting the slow motions of high and distant landslides in remote mountain areas has always been a problem. This paper takes the Woda landslide along the Jinsha River as an example to monitor landslide movement. Although some parts of the landslide body have been found to have moved in recent years, the timing and magnitude of motion have not been systematically monitored or interpreted. Here, we apply the SBAS time series strategy using 65-scene Sentinel-1A/B satellite InSAR images and study the spatial distribution and temporal behaviour of landslide movements between July 4, 2018, and August 29, 2020. Our research results show that the cumulative deformation on the left side of the landslide body with concentrated deformation was approximately 200 mm during the 2-year observation period. By calculating the relationship between the InSAR time series and the precipitation around the landslide, it is found that the landslide deformation is closely related to rainfall. GNSS technology is also deployed on the landslide mass and effectively complements InSAR technology. Simultaneously, based on the results of field surveys and hydrological data analysing the landslide's spatial deformation characteristics and deformation factors, the landslide deformation can also be inferred to be related to precipitation. The method used in this paper can be used for early recognition and early warning of high and remote landslides.