Geological and geomorphological conditions of Archar-Orsoya lowland as a factor for the formation of groundwater chemical composition and in risk of its contamination

The Archar-Orsoya lowland is situated in the Danube floodplain west of the town of Lom, NW Bulgaria. It is aligned in a west-east direction along the Danube River and to the south it is bounded by a high landslide slope, built of Pliocene clays and sands. Parallel to the shore, sand dunes are formed with lowered sections between them, in which there are conditions for swamping. The lowland is made up of the alluvial sediments of the Danube, represented by a lower gravelly-sandy layer and an upper sandy-clayey layer. In the gravelly-sandy layer unconfined groundwater is accumulated, with shallow water table – from 0.5 to 7 m beneath the surface. Groundwater is recharged by infiltration of precipitation, surface water and groundwater, which laterally flows into the alluvium from adjacent aquifers. At high waters, the Danube River suppresses the formed groundwater flow and temporarily feeds it. Due to the described formation conditions in the lowland, the chemical composition of groundwater is formed under the influence of intense dynamics and has a low TDS (total dissolved solids). The shallow groundwater table and the corresponding thin unsaturated zone are a prerequisite for easy groundwater contamination with components entering from the surface. Therefore, a map of depth to groundwater table is drawn to identify the most vulnerable areas.

Finite element modeling of the joint action of flow slide and protective structure

Introduction. In the context of the problem of plane deformation, a finite-element model of a natural landslide slope is developed. It allows for the joint work of a flow slide and a protective engineering structure. The Drucker-Prager model is used to take into account the physical nonlinearity of the slope layer material. To activate the kinematic instability, a viscoelastic interlayer is introduced into the design scheme, along which the landslide layer slides.Materials and Methods. Numerical experiments were performed using the ANSYS Mechanical software package, which implements the finite element method in the form of the displacement method. Slope discretization is performed on the basis of PLANE42 flat four-node finite elements. To simulate the displacement of the landslide layer relative to the fixed base, the combined viscoelastic elements COMBIN14 were used.Results. A physically nonlinear model of a natural landslide slope consisting of a base, a landslide layer, and a viscoelastic interlayer, is formalized. An engineering technique for analyzing the stress-strain state of the “slopeprotective structure” system has been developed, taking into account the kinematic instability of the landslide layer. A series of computational experiments was carried out.Discussion and Conclusion. Based on the calculations performed, it is shown that the proposed method enables to specify the force action of the landslide layer on the protective structure and, thereby, to increase the reliability of the risk assessment when activating the landslide process.

Assessment of the Hydrogeological Conditions of the Territory Adjacent To the Tskneti-Samadlo Highway

The aim of researching the current hydrogeological state of the territory adjacent to the TsknetiSamadlo highway is to present such anti-landslide measures with the help of which normal operating conditions of the highway should be created. The study area is located on the northern side of the southeastern fork of the Trialeti Range, from the slopes of which many deep erosional ravines originate, filled in the spring-summer period with water that flows into the gorge of the r. Vere. The river is the main basis of erosion of the study area. To carry out hydrogeological studies, two water samples were taken - the water found on the landslide slope, which flowed along the surface of the bare slope, and a small amount of ground water from under the slope. The data of the chemical analysis of waters showed that these two samples are identical in chemical composition. The results of the total mineralization correspond to M = 1.9 g / l. Consequently, the water is not suitable for drinking, as it belongs to the category of slightly saline waters and is classified as sulphate-hydrocarbonate calcium-sodium. In addition to water samples along the road, one soil sample was taken to determine the degree of soil contamination. In the extract of a soil sample, the indicator of total mineralization is slightly increased (M = 0.3 g / l), according to its chemical composition, it is classified as hydrocarbonate-sulphate sodium-calcium. With regard to the anti-landslide measures proposed for the investigated area, the main one is the regulation of surface water flows using a system of spillways and drainages, which requires an accurate calculation of the height and steepness of slopes, in addition, maximum preservation of vegetation cover on deluvial slopes is required.

Influence of morpho-evolution on the earthquake-induced mobility of the Albuñuelas landslide (Granada, Spain)

<p>The morphological evolution of landslide slopes is generally controlled by the combination of weathering, tectonics, gravity and river erosion. Among them, seismic shaking plays a fundamental role in landslide activity and mobility in high seismicity regions. It can result in important modifications of landslide geometry and consequently, of its response to external loadings. In particular, morphological changes in landslide slope can imply changes in the interactions between seismic waves and landslide mass, which could theoretically modify the hazard related to the earthquake-induced effects. This study aims at pointing out the effects of slope morpho-evolution on the long-term modification of earthquake-induced landslide dynamics, which is here quantified in terms of expected seismically induced displacements, considering unaltered seismic hazard conditions. The Albuñuelas landslide was selected, located in Andalusia (South Spain) which is one of the most seismic regions of Spain. This landslide is a large roto-translational process whose last earthquake-induced reactivation occurred during the 1884 Andalusia Earthquake (M<sub>w</sub> 6.5), causing relevant damages to the Albuñuelas village. Data available from field surveys and geophysical investigations, allowed to derive the current engineering-geological model of the landslide slope. According to the available geological and geomorphological data, the slope shape was back-deformed to reproduce the landslide geomorphological evolution sequence over time, until its first-time failure. The reconstructed sequence is consistent with a geomorphological evolution mainly driven by the combination of earthquake-induced re-activations and low rates of deformation caused by the intense incision of the Albuñuelas River, responsible for the valley deepening. 2D-dynamic stress-strain numerical simulations were performed on several stages of such sequence applying 17 equivalent signals derived following the LEMA_DES (Levelled-Energy Mutifrequential Analysis for Deriving Equivalent Signals) approach with an Arias Intensity of 0.1 m/s, according to the Andalusia regional seismic hazard. The outputs were expressed in terms of seismically induced displacements vs. characteristic periods diagrams, in order to highlight the role of signal frequency content as well as the effect of the landslide 2D-geometry (T<sub>l</sub>) and thickness (T<sub>s</sub>) on the resulting displacements. Since the morpho-evolution resulted in a progressive increasing of the landslide mass length and its dislodgment into several blocks since the first-time failure, the landslide mobility was analysed over time at each single-block scale. The comparison revealed a not neglectable modification of the Albuñuelas landslide susceptibility to the local seismic hazard over time, highlighting the necessity to understand the mechanisms driving the natural system evolution to provide more reliable earthquake-induced hazard scenarios.</p>

JUSTIFICATION OF STRENGTHENING A SLIDING BRIDGE SUPPORT (ON THE EXAMPLE OF THE BRIDGE THROUGH THE R. IZHORA ON THE HIGH-SPEED ROAD SAINT PETERSBURG - MOSCOW)

The article describes the experience of strengthening the foundations of the bridge support laying on a landslide slope. The bridge under consideration crosses the river Izhora in the Leningrad region. Numerical modeling of the process of development of support deformations is carried out. Analysis of the calculations showed that the development of the landslide process occurred as a result of waterlogging of the soil massif and soaking of soils at the base of support No. 10. Structural strengthening of the support in the form of buttresses was developed and numerically substantiated to eliminate deformation of the bridge support.

Mathematical modeling study of the landslide state of the slope of the mountain "SHYM BULAK"

The data on the main causes of the causing landslide on the mountain slopes, in particular, the pictures of the landslide-collapse that occurred along the road between the Medeu dam and the Shym Bulak ski sports complex in the gorge of the high slopes of the Trans-Ili Alatau in Northern Tien Shan, are given. It also offers some data on the physical and mechanical properties of loess and loamy soils, with which the cover soils of these slopes are mainly composed. A finite-element model for the study of the stress-strain state (VAT) of soil deposits of slopes of an obliquely layered structure is proposed with instructions on the features of using isoparametric elements of a quadrangular shape with four nodes of an arbitrary shape. The landslide slope of the mountain is modeled by finite elements together with the highway and the lower slope at the foot of which the Kishi Almaty River flows. The results of the VAT study are presented and the places of the slope that are vulnerable to a landslide are identified as dangerous.

The North Saskatchewan River Valley Landslide: Slope and Pipeline Condition Monitoring

Following a loss of containment incident in July 2016 on a 16-inch diameter pipeline on the south slope of the North Saskatchewan River located in Saskatchewan, Canada, Husky completed extensive studies to understand and learn from the failure. The cause of the incident was ground movement resulting from a landslide complex on the slope involving two deep-seated compound basal shear slides as well as a near surface translational slide in heavily over consolidated marine clays of the Upper Cretaceous Lea Park Formation. One aspect of the studies has been to undertake structural analysis of the pipeline response to the loading imposed from the ground movement to minimize the potential for a similar occurrence from happening in the future and determine the integrity of the pipeline at the time of the assessment. Given the scale and complexity of the landslide, slope stabilization measures were not practical to implement, so repeat ILI using caliper and inertial measurement technology (IMU), in addition to a robust monitoring program was implemented. Realtime monitoring of ground movements, pipe strain and precipitation levels provided a monitoring and early-warning system combined with documented risk thresholds that identified when to proactively shut-in the pipeline. The methodology and findings of the slope monitoring and structural analysis that was undertaken to examine the robustness of the pipeline to withstand future landslide movement are presented herein. The work involved modelling of the pipeline history on the slope including loads that had accumulated in the original pipeline sections based on historical ILI results and slope monitoring. The pipeline orientation was parallel with the ground movement in the landslide complex, so the development of axial strain in the pipeline was the dominant load component, which are particularly damaging in the compression zone. The work provided recommendations and technical basis to continue safe operation of the pipeline with consideration of continuing ground movement and assisted the operator with decisions over the long-term strategy for the pipeline.