Stability evaluation of hazardous translational slide zones in part of Yamunotri Pilgrimage route, National Highway 507, Uttarakhand, India

Slope failure is a widespread phenomenon in Lesser Himalaya owing to its fragile tectonic settings, rugged topography, high relief, abruptly varying gentle to steep slopes and peculiar climatic conditions. Road development and urban expansion have further deteriorated the slope conditions. National Highway 507, a part of the pilgrimage route to Yamunotri in Uttarakhand, is one such route, experiencing hostility from frequent slope failure episodes that are causing havoc for villagers and pilgrims. In the present study, the four most hazardous translational slide zones in the 22 km stretch from Judo to Kandi village in the Yamunotri pilgrimage route has been identified, for detailed geotechnical investigation and slope stability assessment applying different approaches. The rock masses of this region are inherently weak owing to their closeness to Aglar fault and other joints and fractures. Rock mass classification systems are used to assess the stability and for estimating strength parameters, viz. cohesion and angle of internal friction, essential for the factor of safety determination. They are slightly varying due to the relatively homogeneous grain size distribution and mineralogical composition of rock masses. Kinematic Analysis differentiated the type of failure as planar or wedge and, accordingly, factor of safety is determined by limit equilibrium approach. The factor of safety, computed strength parameters, discontinuity and slope properties, varies from 5.9 to 1.1 in dry conditions while it reduces below unity as the saturation upsurges. It depicts stable conditions in dry conditions but water penetration and saturation along the cracks and discontinuities during rainfall make them unstable. Close vicinity with fault, steep slope, presence of joints and weathered lithology are dominating factors initiating the instability in route with further aggravation by rainfall, road widening and urban expansion.

Reactivation of Ancient Landslide Deposits: Geological Characteristics and Deformation Mechanism

The ancient Zhenggang landslide (47.5 million m3) represents a potential threat to the construction and safe operation of the proposed Gushui Hydropower Project and to the people living downstream. The landslide was caused by continuous rainfall from October 20 to November 5, 2008, indicating that groundwater aggravated sliding and deformation, and it can be divided into two distinct zones: zone I and zone II. Investigations of the Zhenggang landslide deposits have been conducted for 10 years, but the evolution of the landslide deformation is yet to be revealed. Geological surveys and stability analysis have revealed that the Zhenggang landslide is currently relatively stable and is not sliding. The deformational data for the deep soil layers show that subslide zone I is a translational slide, while subslide zone II is an uplift slide, and zone II is slightly more stable than zone I. Obvious interior deformational failure occurred and was observed in the exploratory adits. The numerical results show that rainfall infiltration is the main factor to induce the revival of ancient landslide, and it is necessary to strengthen the landslide risk assessment and reliability of Zhenggang landslide under the condition of rainfall infiltration. Finally, in order to reduce landslide risks, the local residents living near the landslide mass should be relocated, and measures should be taken to increase slope stability.

Simulation of a Submarine Landslide Using the Coupled Material Point Method

Exploring the submarine landslide is challenging due to the invisibility nature and the complex soil-water interaction and large deformation throughout its runout process. The purpose of this paper is to investigate the ability of the coupled material point method (MPM) in modeling the soil flows under water. A sand-column collapse experiment is performed fully under water initially, with the results used to benchmark the MPM analysis. Thereafter, the whole failure process of a real submarine landslide in the South Mediterranean sea is simulated using MPM. The results show that MPM can be a reliable tool in capturing the postfailure behaviors of the submarine landslide. The failure mode of the landslide is flow-type, with an initial translational slide moving to a diffusive one eventually.

Tree Ring-Based Estimation of Landslide Areal Reactivation as a Fundament of Magnitude–Frequency Assessment

Magnitude–frequency (M–F) relationships represent important information on slope deformation and are used in hazard assessment or as supporting data for urban planning. Various approaches have been used to extract such relationships in the past, but most of these methods drove at the problem of exact events´ frequency determination. Dendrogeomorphic (tree ring-based) approaches are actually thought to be the most precise method of dating past mass movement events that occurred within the last several centuries. Together with information on the spatial positions of the analysed trees, they represent a potentially very valuable tool for reconstructing M–F relationships, although their use for this purpose has been very rare in the past. In this study, M–F relationships are reconstructed using dendrogeomorphic methods for three landslides of different types (a translational slide, a flow-like slide, and a rotational slide) occurring in different geological materials (thick-bedded flysch, limestone marls, and volcanic breccia). In total, 572 disturbed trees were analysed, and chronologies of mass movement events were built. Landslide magnitudes were expressed in three ways: (i) the value of the standard It index; (ii) the area, as determined using homogenous morphological units; and (iii) the area, as determined using tree buffers. The power-law nature of M–F relationships was confirmed for all the landslides that were studied and using all the approaches that were applied. All of the combinations of results yielded high correlation values; nevertheless, differences were noted. The advantages and limitations of each approach used to reconstruct M–F relationships are also discussed.

Finite Element Modelling of a Series of Ground Displacement Episodes and Stress Relief Procedures

The Wapiti River South Slope (the Slope) near Grand Prairie, Alberta, Canada, is 500 m long and consists of a steep lower slope and a shallower upper slope. Both the upper and the lower slopes are located within a landslide complex with ground movements of varying magnitudes and depths. The Alliance Pipeline (Alliance) NPS 42 Mainline (the pipeline) was installed in the winter of 2000 using conventional trenching techniques at an angle of approximately 8° to the slope fall line. Evidence of slope instability was observed in the slope since 2007. The surficial geology of the slope comprises a colluvium layer draped over bedrock formation in the lower slope, and glacial deposits in the upper slope. Available data indicated two different slide mechanisms. In the lower slope, there is a shallow translational slide within a colluvium layer, and in the upper slope there is a deep-seated translational slide within the glacial deposits. Both the upper and lower slope landslides have been confirmed to be active in the past decade. Gradual ground displacements in the order of several centimeters per year were observed in both the upper and lower slopes between 2007 and 2012. Large ground displacements in the order of several meters were observed between 2012 and 2014 in the lower slope that led to the first stress relief and subsequent slope mitigation measures in the spring and summer of 2014. Monitoring of the slope after mitigations indicated significant reduction in the rate of ground movement in the lower slope. Surveying of the pipeline before and after stress relief indicated an increase in lateral pipeline deformation in the direction of ground movement, following the stress relief. This observation raised questions regarding the effectiveness of partial stress relief to reduce stresses and strains associated with ground movements. Finite element analysis (FEA) was conducted in 2016 to aid in assessing the condition of the pipeline after being subject to ground displacements prior to 2014, stress relief in 2014, and subsequent ground displacement from July 2014 to December 2016. The results and findings of the FEA reasonably matched the observed pipeline behaviour before and after stress relief in the lower slope. The FEA results demonstrated that while the lateral displacement of the pipeline, originally caused by ground movement, increased following the removal of the soil loading during the stress relief, the maximum pipeline strain was reduced within the excavated portion. The FEA was also employed to assess the pipeline response to potential ground displacement scenarios following December 2016. For this assessment, three ground displacement scenarios that comprise different lengths of the pipeline were analyzed. An increased rate of ground displacement, with a pattern that matched one of the analyzed scenarios, was observed in the upper slope in the spring of 2017. The results of FEA were used to assess the pipeline response to the increased rate of displacement in the upper slope. Subsequently a decision was made to stress-relieve the pipeline. The second stress-relief was conducted in the summer of 2017. This stress relief was conducted locally at the toe and head of the active slide in the upper slope, where the FEA showed the greatest stress concentrations in the pipeline.

The Effect of Ground Displacement and Stress Relief on Pipeline Behaviour: A Case Study

The Wapiti River South Slope is located 25 km southwest of Grande Prairie, AB. The slope is 500 m long and consists of a steep lower slope and a shallower upper slope, both of which are located within a landslide complex with ground movements of varying magnitudes and depths. The Alliance Pipelines Ltd. (Alliance) NPS 42 Mainline (the pipeline) was installed in the winter of 2000 using conventional trenching techniques at an angle of approximately 8° to the slope fall line. Evidence of slope instability was observed in the slope since the first ground inspection in 2007. Review of the available geotechnical data indicates two different slide mechanisms. In the lower slope, there is a shallow translational slide within a colluvium layer that is draped over a stable bedrock formation. In the upper slope, there is a deep-seated translational slide within glaciolacustrine and glacial till deposits that are underlain by pre-glacial fluvial deposits. Both the upper and lower slope landslide mechanisms have been confirmed to be active in the past decade. Large ground displacements in the order of several meters between 2012 and 2014 in the lower slope led to a partial stress relief and subsequent slope mitigation measures in the spring and summer of 2014, which significantly reduced the rate of ground movement in the lower slope. Surveying of the pipeline before and after stress relief indicated an increase in lateral pipeline deformation (in the direction of ground movement) following the stress relief. This observation was counter-intuitive and raised questions regarding the effectiveness of partial stress relief to reduce stresses and strains associated with ground movements. Finite element analysis (FEA) was conducted in 2017 to aid in assessing the condition of the pipeline after being subject to the aforementioned activities, and subsequent ground displacement from July 2014 to December 2016. This paper presents the assumptions and results of the FEA model and discusses the effect of large ground displacement, subsequent stress relief and continued ground displacement on pipeline behaviour. The results and findings of the FEA reasonably match the observed pipeline behaviour before and after stress relief. The FEA results showed that while the lateral displacement of the pipeline that was caused by ground movement actually increased following the removal of the soil loading, the maximum pipeline strain was reduced in the excavated portion. The results also indicated that ground displacement in the upper slope following the stress relief had minimal effect on pipe stresses and strains in the lower slope.

Susceptibility to Translational Slide-Type Landslides: Applicability of the Main Scarp Upper Edge as a Dependent Variable Representation by Reduced Chi-Square Analysis

The applicability of main scarp upper edge (MSUE) as dependent variable representation was performed in a translational slide susceptibility zonation of the Milia and Roglio basins, Italy. Two landslide inventories were built thanks to detailed geomorphological mapping and aerial photograph analysis. The landslides were used to create the models before 1975, while those after 1975 were employed to validate the predictive power of the model. Possible landslide-related factors were chosen from a geomorphological survey. The inventory landslide maps and the landslide-related factor maps were processed by conditional analysis, producing landslide susceptibility maps with five susceptibility classes. A comparison between the distribution of landslides after 1975 and those derived from models provided the predictive power of each model, which in turn was used to define the best predictive model. Reduced chi-square analysis allowed to define the efficiency of MSUE as dependent variable representation. MSUE can be applied as dependent variable representation to landslide susceptibility zonation with appreciable results. In the Roglio basin, slope angle, distance from streams, and from tectonic lineaments proved to be the main controlling factors of translational slides, whereas in the Milia basin, lithology and slope angle gave more satisfactory results as landslide-predisposing factors.

Stratigraphy and dating of a large slumping event in the Northern Aegean

Continuous seismic (Air-Gun) subbotom profiling in the N.Aegean was revealed a large submarine translational slide. The failure zone is extended from about 300m depth down to 800 m and covers an area of 85 Km2. The mean thickness of the slide reaches about 55 m and an estimated total volume of 4 Km3 of Quaternary sediments have been slided along a distance of 6 to 7 Km. Chronostratigraphic analysis of the acoustic reflectors imply that the slide plane is the muddy layer of late Pleistocene age (170-240 Ka BP). AMS dating of sediment cores provided indications that this major slide event occurred 5 to 6 Ka BP.

The Verdesca landslide in the Agri Valley (Basilicata, southern Italy): a new geological and geomorphological framework

A landslide, to the west of Montemurro (a small village in southern Italy), has recently caused damage to buildings and other infrastructure in an urbanized area; as a result the development of new economic activities has been prohibited. The landslide phenomenon started in the last century and has been studied since the 1990s using classical geotechnical methods; however the sliding body continues to move. This paper presents the results of a study carried out using field surveys, geognostic investigations and TDR (time domain reflectometry) measurements in order to reconstruct the stratigraphy of the sediments involved and to further understand the geological and geomorphological context of the slope. This study is part of a larger multidisciplinary project, the results of which will also be presented in this paper. The landslide (rotational slide in the upper sector, developing into a translational slide in the lower part) affects Quaternary continental clastic deposits resting on a bedrock formed by Tertiary siliciclastic sediments of the Gorgoglione Flysch. TDR measurements did not show any significant movement during the period monitored (January 2013–January 2014). Slip zone geometries were hypothesized using inclinometric measurements taken from previous studies, stratigraphic data and geomorphological interpretations of topographic scarps. Feedback from monitoring will confirm this hypothesis.