IoT-Based Geotechnical Monitoring of Unstable Slopes for Landslide Early Warning in the Darjeeling Himalayas.

In hilly areas across the world, landslides have been an increasing menace, causing loss of lives and properties. The damages instigated by landslides in the recent past call for attention from authorities for disaster risk reduction measures. Development of an effective landslide early warning system (LEWS) is an important risk reduction approach by which the authorities and public in general can be presaged about future landslide events. The Indian Himalayas are among the most landslide-prone areas in the world, and attempts have been made to determine the rainfall thresholds for possible occurrence of landslides in the region. The established thresholds proved to be effective in predicting most of the landslide events and the major drawback observed is the increased number of false alarms. For an LEWS to be successfully operational, it is obligatory to reduce the number of false alarms using physical monitoring. Therefore, to improve the efficiency of the LEWS and to make the thresholds serviceable, the slopes are monitored using a sensor network. In this study, micro-electro-mechanical systems (MEMS)-based tilt sensors and volumetric water content sensors were used to monitor the active slopes in Chibo, in the Darjeeling Himalayas. The Internet of Things (IoT)-based network uses wireless modules for communication between individual sensors to the data logger and from the data logger to an internet database. The slopes are on the banks of mountain rivulets (jhoras) known as the sinking zones of Kalimpong. The locality is highly affected by surface displacements in the monsoon season due to incessant rains and improper drainage. Real-time field monitoring for the study area is being conducted for the first time to evaluate the applicability of tilt sensors in the region. The sensors are embedded within the soil to measure the tilting angles and moisture content at shallow depths. The slopes were monitored continuously during three monsoon seasons (2017-2019), and the data from the sensors were compared with the field observations and rainfall data for the evaluation. The relationship between change in tilt rate, volumetric water content, and rainfall are explored in the study, and the records prove the significance of considering long-term rainfall conditions rather than immediate rainfall events in developing rainfall thresholds for the region

Approaches of data analysis from multi‐parametric monitoring systems for landslide risk management

In the last decades, several approaches were proposed accounting for early warning systems to manage in real time the risks due to fast slope failures where important elements, such as structures, infrastructures and cultural heritage are exposed. The challenge of these approaches is to forecast the slope evolution, thus providing alert levels suitable for managing infrastructures in order to mitigate the landslide risk and reduce the “response” time for interventions. Three different strategies can be defined in this regard: an Observation‐Based Approach (OBA), a Statistic‐Based Approach (SBA) and a Semi‐Empirical Approach (SEA). These approaches are focused on searching relations among destabilizing factors and induced strain effects on rock mass. At this aim, some experiments are being performed at different scales in the framework of consulting activities and research projects managed by the Research Centre for the Geological Risk (CERI) of the University of Rome “Sapienza”. These experiments are testing different kind of sensors including extensometers, strain gauges, rock‐thermometers, interferometers, optical cams connected to Artificial Intelligence (AI) systems, for detecting changes in rock properties and detecting stressstrain changes, as well as pluviometers, anemometers, hygrometers, air‐thermometers, micro‐ or nano‐ accelerometers and piezometers for detecting possible trigger of deformational events. The results of this Ph.D. thesis demonstrate that the data analysis methods allowed the identification of destabilizing actions responsible for strain effects on rock mass at different dimensional scale and over several time‐window, from short‐ to long‐ period time scale. Furthermore, the three approaches were to be suitable to recognize precursor signals of rock mass deformation and demonstrated the possibility to provide an early warning

Imaging geotechnical property changes during failure development of tropical residual soil slope

Devastating cases of slope failure have been reported in many parts of the world; many of which are in tropical countries where the natural and man-made slopes are mostly made up of red tropical residual soils. Most of the failures occurred following heavy rainfall or during flooding. For this reason, the abnormal change of the soil water content is presumed to be responsible for these failures. It becomes imperative, therefore, to understand the soil-water interaction and eventual failure process in tropical residual soil, if this problem is to be effectively tackled. To achieve this aim, a research was conducted on a systematically designed and constructed slope model of a simulated tropical residual soil slope. Preliminary studies were conducted to assess the suitability of the selected material, methodology and instrumentation to be used in the experiment. This was followed by a trial experiment on a small-sized model with a surface area of 200 mm x 370 mm and a maximum (crest) slope height of 220 mm. This small size allowed easy handling and repeatability but could not accommodate enough instrumentation, due to the limited size. To remedy this deficiency, another experimental trial was conducted on a larger-sized model constructed in a square fibreglass box with surface area of 1315 mm x 1315 mm and the maximum height of this slope was 650 mm. Before conducting the final laboratory experiment, the model was analyzed and designed with the aid of modelling software (i.e. SLOPE/W, SEEP/W and SIGMA/W). The geotechnical tests and other preliminary laboratory studies conducted at the beginning of the study provided necessary inputs during numerical modelling. This numerical modelling produced a final workable model and provided an idea about the failure mechanism of the designed model. Finally, the main experiment was conducted on the designed model which was constructed in a large acrylic glass. The surface dimension of this model was 1000 mm x 1700 mm and the maximum slope height was 750 mm. In all the trials, a slope failure was caused by supplying water through a supply chamber, provided by the side of the crest, and allowing it to move freely to the toe. The geophysical changes and physical deformation during failure were observed using an integrated system of electromagnetic sensors (5TE and MPS6), electrical resistivity, and cameras. From the results presented and discussed, it was understood that the gradual movement of water through the slope caused a gradual reduction in matric suction, with the consequent reduction of shear strength and eventual slope movement. The physical deformation began with an initial settlement and minor surface cracks; which continually progressed to excessive settlement and larger cracks, before the final forward movement. The excessive settlement prior to the final movement appears to be associated with a soil structure collapse induced by wetting; while the forward sliding is caused by the movement of water, which tends to pull the slope downwards. The experiment provided an improved knowledge of the slope failure mechanism in tropical residual soils and has established the suitability of geophysical methods for monitoring the stability of the slopes and embankments of the tropics

Quantifying hillslope response to glacier retreat : landslide mechanics, processes and impacts : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physical Geography at Massey University, Palmerston North, New Zealand

The published versions of Chapter 3 and Chapter 5 may respectively be found at: 10.1007/s10346-019-01316-2 and https://doi.org/10.1016/j.geomorph.2020.107411.Fig 2-4 (=Wohl et al., 2019 Fig 4) was removed for copyright reasons.Landslides are a natural hazard experienced in all countries around the world. Their formation is heavily influenced by internal and external processes including geology, earthworks, rainfall and in some instances glacier ice. This thesis investigates the response of alpine hillslopes to glacier retreat through the utilisation of movement monitoring techniques, subsurface investigations and geotechnical slope stability analysis. Three objectives are proposed and guide the research outcomes of this thesis. The first objective is to investigate the underlying preconditions, preparatory factors and triggers which control and enhance paraglacial rock slope failures through the study of the Mueller Rockslide in New Zealand’s South Island. Preconditioning and progressive weakening of the rockslide began over 8000 years prior to current glacier retreat, with the rockslide forming ~7500 years ago. Movement monitoring shows the rockslide to accelerate gradually over its history, culminating in maximum movement rates of ~6 m per year. Movement is constrained along structurally conditioned discontinuities, identified through a novel ground investigation combining geophysical and geotechnical techniques. Glacier debuttressing is considered a primary trigger of controlled slope failure, with increased displacement in spring attributed to snow melt and rainfall. Step-path failure of the rockslide is ongoing with tensile stress accumulating in the landslide body leading to segmentation of the rockslide into four zones. Ongoing progressive failure will likely lead to block sliding of the rockslide. The second objective of this thesis was to identify drivers of movement in paraglacial sediment slopes. A novel suite of monitoring techniques was used at Fox Glacier which showed clear correlation between hillslope failure and glacier retreat and downwasting. Unlike previous studies, this thesis found debuttressing to be the primary trigger of slope failure with rainfall acting as an accelerant. Debris flows, once thought to be a dominant process in sediment slope adjustment did not begin until debuttressing was completed. Finally, this thesis investigated the potential impacts of paraglacial landsliding on the broader environment. Both the rock and sediment slope failures in this study have deformed their supporting glaciers and a combination of monitoring techniques have uncovered to how sediment is delivered to the proglacial zone. Due to both sites being located within a high seismic hazard zone, catastrophic failure of both sites is possible. Continued failure of the Mueller Rockslide will likely result in a landslide dam and will also lead to continued retrogression of the headscarp and weakening of the surrounding hillslope. Continued failure of the sediment slopes at Fox Glacier will contribute large volumes of sediment to the proglacial zone, allowing for remobilisation of sediment in flood conditions. Both landslides have apparently created morphological change in their supporting glaciers. A unique combination of monitoring methodologies was used to provide insight into landslide movement and evolution, but their usage should not be limited only to studies of landslides. The methodologies used in this thesis provided context across a range of spatial and temporal scales