Geophysical investigation of a large landslide in glaciolacustrine clays in the Trièves (original) (raw)
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Engineering Geology, 2009
Slope movements in clay deposits are world widespread and result from complex deformation processes, including internal strains in the landslide body and slipping along rupture surfaces. Such mass movements are likely to generate changes in the geophysical parameters characterizing the ground, which can be used to map the landslide body. In the last decade, geophysical techniques have been increasingly used for landslide investigation purposes. However, the success of any geophysical technique is overall controlled by the existence of a geophysical contrast differentiating the body to be mapped. For landslides affecting thick clay materials (from soft clay to shale or marl), electrical and seismic techniques have been mainly applied in the past. In this study, we attempt to physically characterize the deformation within a large slide (Avignonet) affecting laminated clays which were deposited in a glacially dammed lake during the Würm period. Clay deposits, which cover an area of 300 km 2 south of Grenoble (French Alps) and have a maximum thickness of 200 m, overlay compact alluvial layers and marly limestone of Mesozoic age. Piezometric data at Avignonet show that the water table is very shallow, implying that the slide developed in saturated clay. Several seismic and electrical profiles were performed in order to tentatively correlate the variations of P-wave velocity, S-wave velocity and electrical resistivity with geotechnical data and morphological observations. In such saturated and fine material, it turned out that only the S-wave velocity (Vs) exhibits significant variations with the displacement rates and the morphological features. Vs values at shallow depth were found to be inversely correlated with displacement rates measured by GPS, with a division by at least a factor of 2 between the zones unaffected and strongly deformed by the landslide. These results suggest that Vs mapping could provide valuable information on the deformation state of the clay material and that the evolution of Vs with time could be used as an indicator for characterizing the landslide activity at depth, including the evolution into a flow.
Landslides and Geophysical Investigations: Advantages and Limitations (Editorial)
International Journal of Geophysics, 2019
Geohazards processes can damage or increase the risk of human beings, properties, critical infrastructures, and environment itself. ey also could involve the interruption of human activities with serious socioeconomic consequences. Among all the natural occurrences, landslides are regarded as one of the most destructive types of geohazards. Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct influence of gravity, which can occur and develop in a large variety of volumes and shapes. Even though the catastrophic impact of landslides is not totally unavoidable, it can be significantly reduced by increasing the capacity to assess and predict the risks and using different mitigation methods. In the past decades, many D and D numerical modelling methods have been designed and developed to assess slope stability, to predict slope response to various triggers, to evaluate the slope deformation and evolution pattern, and to perform back-analysis simulations. Nevertheless, such models still require access to detailed knowledge of the geological, mechanical, and hydrological properties of landslides and boundary conditions. erefore, accurate geological field surveys have to be integrated by means of low-cost and noninvasive techniques, like the geophysical ones, to collect widespread data with the aim of reconstructing a suitable geological and hydrogeological model of the area, improving the reliability of deterministic model. is special issue is dedicated to the geophysical methods applied to investigate, characterize, and monitor landslides. Over the years, both the advantages and limitations of these techniques have been highlighted, and some drawbacks are still open. Some papers were submitted to this special issue, and, aer a thorough peer review process, only five articles were selected to be included in this special issue. is relatively small number is probably caused by the difficulty in applying geophysical techniques on slope movements given hard-operating conditions (e.g., high slopes, distance from access roads, and lack of security for the technical operator) and not because the methods limitations are greater than the advantages. e review carried out by V. Pazzi et al. on geophysical techniques applied in landslides studies analyses the international efforts toward overcoming the geophysical technique limitations highlighted by the geophysics and landslide review, focusing on works of the last twelve years (-). e authors carried out the review analysis using a "material landslide approach" on the basis of the more recent landslides classification. e most studied landslides are those of the flow type for "soil" landslide typology and those of the fall type for the "rock" category. From the "employed method" point of view, active and passive seismic methods are the most employed in landslide characterization and monitoring. To quantify the efforts performed to overcome the limitations highlighted in , a three-level scale was employed (from many/some efforts to non-discussed). e limits inherent in each technique and the need to still develop multisource data integration methods were clear; very oen
Analysis of a retrogressive landslide in glaciolacustrine varved clay
Engineering Geology, 2010
The largest landslides in Estonia are associated with glaciolacustrine varved clays. One of the recent slope failures, Audru landslide, was chosen for detailed investigation. Landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay. Varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body. Field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events. The first stage of Audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body. The influence of the various modeling parameters on the overall slope stability was also investigated.
Geophysical investigation of landslides : a review
Bulletin de la Soci�t� G�ologique de France, 2007
In the last two decades, shallow geophysics has considerably evolved with the emergence of 2D spatial imaging, then 3D spatial imaging and now 4D time and space imaging. These techniques allow the study of the spatial and temporal variations of geological structures. This paper aims at presenting a current state-of-the-art on the application of surface geophysical methods to landslide characterization and focuses on recent papers (after 1990) published in peer-reviewed International Journals. Until recently, geophysical techniques have been relatively little used for the reconnaissance of landslides for at least two main reasons. The first one is that geophysical methods provide images in terms of physical parameters which are not directly linked to the geological and mechanical properties required by geologists and engineers. The second reason shown through this study probably comes from a tendency among a part of the geophysicists to overestimate the quality and reliability of the results. This paper gave the opportunity to review recent applications of the main geophysical techniques to landslide characterisation, showing both their interest and their limits. We also emphasized the geophysical image characteristics (resolution, penetration depth) which have to be provided for assessing their reliability, as well as the absolute requirements to combine geophysical methods and to calibrate them with existing geological and geotechnical data. We hope that this paper will contribute to fill the gaps between communities and to strength of using appropriate geophysical methods for landslide investigation.
A Review of the Advantages and Limitations of Geophysical Investigations in Landslide Studies
International Journal of Geophysics, 2019
Landslide deformations involve approximately all geological materials (natural rocks, soil, artificial fill, or combinations of these materials) and can occur and develop in a large variety of volumes and shapes. The characterization of the material inhomogeneities and their properties, the study of the deformation processes, and the delimitation of boundaries and potential slip surfaces are not simple goals. Since the '70s, the international community (mainly geophysicists and lower geologists and geological engineers) has begun to employ, together with other techniques, geophysical methods to characterize and monitor landslides. Both the associated advantages and limitations have been highlighted over the years, and some drawbacks are still open. This review is focused on works of the last twelve years (2007-2018), and the main goal is to analyse the geophysical community efforts toward overcoming the geophysical technique limitations highlighted in the 2007 geophysics and landslide review. To achieve this aim, contrary to previous reviews that analysed the advantages and limitations of each technique using a "technique approach," the analysis was carried out using a "material landslide approach" on the basis of the more recent landslides classification.
Geometry and kinematics of a landslide surface in tertiary clays from the Duero Basin (Spain
Engineering Geology, 2009
The Peñalba roto-translational landslide is one of the large landslides that can be observed in the central area of the Duero Basin (Spain). Its present morphology is a semicircular-shaped depression in which more than 6 m of vertical movement have been measured. The erosion of the banks of the Duero River affecting the slope of the Peñalba Hill has incised vertical cliffs where a slip surface outcrops and can be observed. Currently, the incision level of the Duero River is located 22 m below this surface. The slip surface, on the translational zone within a large roto-translational landslide, developed within the Dueñas Facies in a single bed with a high PI (39.0-47.8) and lower carbonate contents, would have behaved as low-shear strength surfaces (ϕ′ R = 18°-21.8°). At Peñalba, the slip surface and the deformation structures related to it have been exceptionally well preserved. The structures observed are similar to those usually described in shear zones of tectonic origin: an S-C fabric, related to progressive simple shear, and C′ planes, called extensional crenulation cleavage. These similarities suggest that analogous kinematic processes would have taken place in completely different geodynamic environments. In the present work, we have adopted a structural geological-kinematic approach to explain the development of the features in this roto-translational landslide.
Dynamics of slow and fast landslides
International Society for Soil Mechanics and Geotechnical Engineering Online Library: 13th International Symposium on Landslides ( XIII ISL), 2020
The paper discusses some factors that control the shearing soil behaviour and the dynamics of landslides: strain-, strain rate-, and temperature effects. The strain rate effect on residual strength is discussed through shearing tests reported in the literature on saturated samples at velocities ranging from 10-5 mm/min to 10 4 mm/min. Such range covers from very slow to very rapid landslides according to landslide classification. The analysis of available data is presented and provides a framework which helps to define the constitutive law and phenomena further selected for the landslide analyses. Some recent experimental published works are also discussed to show the temperature effect on shear strength. It is concluded that temperature effects are strain-rate dependent. The available data on that is limited and it may have a relevant effect in shallow landslides in which the sliding surface suffers the influence of weather induced temperature changes. The second part of the article focusses on the analysis of landslides including several factors affecting the available shearing strength of the soils involved in instabilities. The motion from triggering to the final re-established equilibrium of slow and rapid landslides is analyzed through academic and simple examples as well as documented real cases. Under some hypotheses to simplify the problems, governing equations are solved analytically or in a simple numerical way to facilitate the discussion and to perform sensitivity analyses. With the interest of evaluating more realistic cases, some simplified hypotheses are relaxed and complex geometries and conditions are taken into account through numerical modeling. The material point method is selected. The MPM numerical codes, recently developed, can deal with strain-and strain-rate dependent shearing strength and include coupled effects likely developed during motion in landslides. Strain-softening of shear strength causing progressive phenomenon is firstly discussed not only because of its effect on triggering first failures, but also for the estimation of landslide run-out. Compound landslides are specifically analyzed to discuss the progressive phenomena developed along internal shearing planes. Peak and residual strength envelopes control the landslide acceleration. The magnitude of the strength drop correlates well with the run-out. Including a strain rate hardening component to the strength allows the assessment of creeping landslides. Weakening phenomena inducing the acceleration of landslides are not directly included as an intrinsic feature. The loss of residual strength that may lead to a rapid landslide is explained by invoking thermal water pressurization. Both effects, strain rate hardening and hydro-thermal coupled weakening, are probably present during motion. Soil properties, landslide features, and external conditions will determine the landslide motion. This interaction is discussed in terms of run-out and velocity of landslides subjected to static conditions, as well as seismic actions. Normalized residual shear stress (V=0.01-0.025 mm/min) Displacement rate (mm/min) Brown London clay-Petley et al. (1966) Muscovite <6um Kenney et al. (1967) Na-Hydrous mica 0.5 M.-Kenney et al. (1967) Na montmorillonite 0M. <2um-Kenney et al. (1967) Na montmorillonite 0M.<0.1um-Kenney et al. (1967) Ca montmorillonite 0M. <2um-Kenney et al. (1967) Selnes quick clay-Kenney et al. (1967) Kaolinite-Kenney et al. (1967) Vajont < 60um-Kenney et al. (1967) Boom clay-De Beer (1967) Boom clay-De Beer (1967) Silty clay-Ramiah et al. (1967) Pepper Shale-La Gatta (1970) Crushed cucaracha shale-La Gatta (1970) Blue London clay-La Gatta (1970) Bearpaw shale-La Gatta (1971) Clay-Bucher (1975) San Francisco mudstone-Pyles (1984) Clayey sandy silt-Salt (1988) Velocity scale Soils exhibiting positive rate effect-Tika et al. (1989a, 1989b) Soils exhibiting negative rate effect-Tika et al. (1989a, 1989b) Soils exhibiting neutral rate effect-Tika et al. (1989a, 1989b) Shiraishi Landslide-Wang et al. (2010) Clayey siltstone, siltstone neutral effect-Lemos (1986) Clayey siltstone, siltstone negative effect-Lemos et al. (1989) Fiji (A)-Lupini (1981) Lower cromer till-Lupini (1981)