Resumo em Inglês:

Abstract Landslides are widespread all over the world, often causing significant consequences in terms of loss of life and property damage. This explains why many scientists from Geology and Geotechnics have long been engaged in solving complex problems of both theoretical and practical interest. Geologists have systematically investigated the common characteristics of landslides proposing several classification systems, while not providing general laws for the triggering and evolution stages. Geotechnical engineers have implemented models to quantitatively analyze these stages but not to develop a general framework for typical landslide behaviors. Aimed to bridge the scientific branches dealing with landslides and based on the past efforts of many researchers all over the world, this paper focuses on deep-seated landslides developing along an existing and/or a new slip surface and multiple shallow landslides that may involve large areas in short periods of time. Considering that these phenomena are often analyzed at one single topographical scale and through monodisciplinary approaches, the paper proposes a new vision that highlights the possibility of a landslide management modern and open to the advanced technologies.

Resumo em Inglês:

Abstract This study was carried out in an instrumented and monitored embankment divided into two symetrical sections and constructed with compacted treated soils (i.e., a silty soil and a clayey soil) exposed to the same atmospheric conditions in a continental climate, with oceanic influences. It aimed to investigate changes of bare soil surface moisture (w) and corresponding suction (s) as result of soil water evaporation processes on a monthly time scale. Seasonal variations in the w (and s) measurement in both soil surfaces show overall consistency with the meteorological measurement within the study area. The paper also examines the ability of four air temperature-based potential evaporation (PET) formulations to capture the process of evaporation at the site. Results indicated that soil water evaporation is controlled by both atmospheric and soil conditions. And, during the most significant drying time period, the measured s consistently increased and the corresponding w decreased suggesting a relatively significant water evaporation effect. However, the monthly predicted PET data varied from a maximum of over 120 mm/month to less than 50 mm/month during the drying time, depending on the used method. The continuously monitored soil surface suctions are used for discussing the variations of evaporation according to the predicted PET method and time period at the site.

Resumo em Inglês:

Abstract The breakwater failure at the Sergipe Harbor is a well-known event among the Brazilian geotechnical community, which provided great knowledge about the behavior of embankments on soft soils, although some questions still remain, since the back analysis diverged from the field outcome. In this context, this work aims to carry out a numerical analysis of the construction of the breakwater using the finite element method to understand the mechanisms of failure. A fully coupled flow-deformation analysis was performed in Plaxis 2D software, using the Soft Soil Creep and Mohr-Coulomb constitutive soil models. The Volume Method was also applied to estimate the stability of the slopes, from the calculated numerical displacements. The interpretation of the results allowed to verify that the analysis simulated behaviors that had been raised as responsible for the failure. High excess pore pressure levels were generated in the phase at which failure occurred, in addition to a strain softening behavior, which, alongside the progressive failure, could justify why the back analysis considering unrealistic gains in undrained strength, calculated by the increase of the vertical effective stresses, had provided missed factors of safety. Although shear deformations and horizontal displacements were verified for both sides of the breakwater, the “shared failure” assumption could not be verified, since the shear stress was mobilized in the rockfill.

Resumo em Inglês:

Abstract This work is part of the review of methodological procedures for the analysis and classification of terrain susceptibility to shallow translational landslides, following the geo-hydro ecological approach. The pilot area is located in Nova Friburgo (RJ), specifically in the D’Antas Creek basin (53 km2). At this stage of the work, geomorphological parameters and indices were evaluated, including slope angle, curvature, drainage efficiency index (DEI) and topography position index (TPI), seen as relevant in regulating the hydrological and mechanical behavior of soils. The results obtained were intersected with an inventory of landslide scars (n = 382) referring to the extreme rainfall event in January 2011, which occurred in the highland region, called Região Serrana, of the state of Rio de Janeiro. This intersection allowed an evaluation between these parameters and the slopes rupture. The concentration of landslide area per class subsidized the establishment of weights for each of the adopted classes, based on the AHP method. A readjustment of the slope angle classes was proposed, as well as the inclusion of the standard curvature in the construction of the Hydro-Geomorphological Conditions Map. The results were promising, with a concentration of 88.74% (0.85 km2) of the landslide areas in the class of high erosive potential.

Resumo em Inglês:

Abstract The slope stability analyses are important to predict environmental, financial, and human life impacts. The Limit Equilibrium Method (LEM) is commonly used to estimate a slope’s Safety Factor (SF). However, the Finite Element Method (FEM) is increasingly applied to slope stability analyses, using different approaches, among which the technique of Shear Strength Reduction (SSR) is commonly used in perfectly plastic elastic models. The objective of this study is to present a discussion about these two methodologies, using critical state models with or without hardening will be used to model the stress-strain behavior of the soil mass. The results obtained in the case study presented, using LEM and FEM considering critical state models with and without hardening are consistent and allowed verifying the stability condition of the slope. Also, the reduction factors are smaller when compared to the results using perfectly plastic elastic models.

Resumo em Inglês:

Abstract Oil production in offshore regions involves the transportation of oil and gas in submarine pipelines, which are vulnerable to geological processes triggered by subsurface oil production like fault reactivation. The fault reactivation process can lead to phenomena that impact the seabed, like subsidence and fluid exudation, and can trigger instability of submarine slopes, which can result in environmental and economic damage. The present work addresses a coupled hydromechanical numerical modeling of a hypothetical case involving fault reactivation caused by oil reservoir production and its impact on an overlying submarine slope. The hypothetical case was simulated using a finite element model. The case involves a reservoir which is cut by a fault zone that reaches the seabed. The slope instability studied was induced by the injection and production of fluids in the reservoir. The fault zone is assumed to be a sealing region and a geomechanical and pressure field discontinuity within the reservoir. Int this work was used the Mohr-Coulomb elastoplastic model with Perzyna viscoplastic regularization to represent the behavior of the fault zone and the overlying submarine slope. Results showed that the fault reactivation, caused by the reservoir production, developed shear stress and shear plastic strain along the fault and through the submarine slope, causing horizontal and vertical displacements in the slope mass and acting as a trigger factor for slope stability. Pore pressure increase at the bottom of the slope structure correlated with the injection pressure artificially increased into the reservoir.

Resumo em Inglês:

Abstract Dynamic soil parameters such as the shear modulus suffer degradation while damping in soil increases under dynamic loading. These can be determined from various tests such as element tests, field tests and centrifuge experiments. Most of the studies about dynamic soil characterization have focused on evaluating these parameters assuming horizontal ground conditions without considering the effect of static shear stresses induced by ground inclination. This paper presents a dynamic centrifuge test conducted on a layered gentle slope comprising clay and sand, to obtain experimental data in terms of shear modulus and damping for various shear strains. Particle Image Velocimetry (PIV) was employed to measure the displacements and to calculate accelerations due to seismic loading at various depths throughout the slope model. The results suggest that the static shear stress caused by the profile inclination causes a more pronounced degradation of the shear modulus when compared to flat ground conditions. Moreover, the damping during the centrifuge test exhibited larger values than expected, following a similar behavior observed in other experimental programs. The strain rate analysis revealed the mobilization of shear stresses higher than the monotonic shear strength for the clay layers during the seismic shaking.

Resumo em Inglês:

Abstract The slope stability is an important topic because it presents risks of socio-economic losses caused by eventual ruptures. It is necessary to identify the site profile, as well as obtaining soil strength parameters for the slope stability analysis. This paper presents and discusses the use of the Flat Dilatometer Test (DMT) in the geotechnical site characterization for slope stability analysis in an unsaturated tropical soil site. Six DMTs were performed to define the stratigraphical profile and estimate geotechnical parameters. Shear strength parameters were determined in the laboratory using saturated and unsaturated triaxial compression as well as soil water retention curves (SWRC) to support DMT data interpretation. A commercial software was used to perform the slope stability analysis a cut slope with 6.6 m height and a gradient around 55° to illustrate the application of DMT and triaxial test data. The DMT allowed the representative site profile to be identified, as well as estimating the design parameters that compared well to those interpreted from unsaturated triaxial test data for the in-situ soil suction. The DMT can be used as logging test in the preliminary characterization of studied site specially to define the stratigraphical profile, site variability, select the regions to collect disturbed and undisturbed soil samples and as the first attempt to estimate the geotechnical design parameters via correlations. It is important to emphasize that laboratory tests on undisturbed soil samples are essential in the slope stability analysis of unsaturated tropical soil profiles.

Resumo em Inglês:

Abstract Stability analyses of slopes in soft soils are usually affected by strain-softening, resulting in unrealistic (unconservative) safety factors. The loss of post peak strength cannot be accounted for by classic limit equilibrium analyses. In practice, however, the overall loss of soil strength is generally approximated by Bjerrum correction factor μ ≤ 1, which is believed to account for the different failure velocities during the field tests (usually vane tests) and the actual failure in the field, in addition to anisotropy (Schnaid & Odebrecht, 2012). The objective of this work is to demonstrate that strain-softening reduces the overall safety factor to a value nearly equivalent to the application of Bjerrum’s correction factor. To accomplish this, a simple constitutive model (Mohr-Coulomb with residual stress) is used for total stress finite element analyses by means of the concept of “equivalent sensitivity” proposed by Pereira Pinto (2017). The results showed that equivalent sensitivity can be a great instrument to simulate the strain-softening behavior of soft soils.

Resumo em Inglês:

Abstract Coastal zones are of great interest in civil engineering due to their economic relevance and active geological dynamics. In Brazil, the development of these regions is related to the use of their geomorphological features in the landscape, among which the cliffs stand out. Although there are studies that consider the influence of the wetting front in stability analysis with cliffs, in general, the studies only consider extreme saturation situations (dry and saturated). In this sense, the present study aims to understand the influence of the wetting front and the degree of saturation reached by the materials in the stability of cliffs composed of Barreiras Formation soil. The stability analyses were carried out using the limit equilibrium method and stress analysis, varying the degrees of saturation of the materials and wetting fronts of a model of a cliff located at Praia de Tabatinga, State of Rio Grande do Norte, Brazil. Failures were identified, in different wetting fronts, by the limit equilibrium method from degrees of saturation around 20%, and by the stress analysis method around 40%. Thus, it was concluded that the variation in the degree of saturation has a preponderant effect on the destabilization of a cliff, since partial saturations are already enough to trigger significant mass movements. It was also noticeable that the wetting front is a relevant effect on instability, although conditioned to the degree of saturation reached, which may enhance the order of magnitude of the identified failures.

Resumo em Inglês:

Abstract The Ramal Trem Turístico (RTT), a 17 km long railway between Ouro Preto and Mariana, a centenary line, currently in operation as a tourist attraction with historical importance. The railroad was built along a steep region, with hundreds of slopes, and eventually slope instabilities compromised the tour. In linear infrastructure projects, a risk assessment is an important tool for risk management, mapping it is the first step. After slope instabilities in 2019, a risk map was elaborated early 2021 for RTT. Risk is obtained by multiplying the probability of a certain event to occur by its consequences. Define its value in a quantitative way demands geotechnical investigation, for precise failure probability. Regardless of its importance, its determination needs high resources, specially for linear infrastructure in a region with heterogeneous geology and pedology. Therefore, for the risk mapping of the RTT, a semi-empirical methodology was adopted, based on the Rockfall Hazard Rating System (RHRS), originally developed for rocky slopes, and adapted for the registration of slopes in soil and in landfill. The aim of the method is to register a series of slope characteristics to be assigned a specific score, framing the slopes within pre-defined risk classes. This methodology was applied to this 17 km railway and identified 286 slopes. In January 2022 extreme rainfall triggered slopes instabilities at RTT. A critical analysis of this event shows a satisfactory result for the applied methodology. Risk mapping is an important tool for risk management, helping to prioritize investments in mitigation measures.

Resumo em Inglês:

Abstract In this case study of a soil nail retaining wall, the measured horizontal displacement is of the order of 0.023% H, where H is the excavation depth, while the two-dimensional Finite Element Method (FEM) analysis suggests horizontal displacements of the order of at least 0.5% H. This study aims to understand which parameters influence such displacements through a Sensitivity Analysis. In addition, the study compares results obtained through two-dimensional and three-dimensional FEM analyses for this case. It concludes that Young's Modulus (E) and the in-situ earth pressure coefficient (K0) are the two parameters that most influence such displacements. This study shows that Mohr Coulomb's perfectly plastic Elastic Constitutive Model is unsuitable for simulating this structure, which had minimal displacements in situ, suggesting the Hardening Soil model (Schanz et al., 1999) as a viable alternative. Compared to 3D analysis, 2D analysis showed significantly larger horizontal displacements. This led to the conclusion that 2D analysis in MEF is unsuitable for predicting lateral displacements unless a Reduction Factor (FR) ranging from 0.4 to 1.0 was applied.

Resumo em Inglês:

Abstract This article presents the case study of Wall C11 of Lot 1 in the ringroads of Caraguatatuba and São Sebastião job site, whose original design consists of an anchored retaining wall with a concrete face supported on root piles. At the time of its interruption, only a part of the job had been executed. The alternative solution, mainly aimed at speeding up the completion of the job, was the execution of reinforced backfill with geogrids behind the concrete wall, eliminating the need for the remaining anchors. The presence of the bedrock top very close to the face of the retaining wall at some points could compromise the anchorage length required for the geogrids. In the construction phase, tests were carried out to verify the elements already executed, specially, the anchors. During the execution of the reinforced soil and after its completion, the instrumentation followed the displacements in the concrete wall.

Resumo em Inglês:

Abstract In Brazil, landslides are frequent, causing deaths and property damage, and occur under the influence of natural and/or anthropic conditions. Rain acts as the main non-anthropic agent in triggering this phenomenon. Because of this, the prediction of landslides becomes an essential tool for managing high-risk areas. The Metropolitan Region of Recife (MRR) has a large history with numerous cases of mass movements over the years. Currently, research points out improvements in the quality of forecasts by including hydrological information, such as soil moisture, in warning systems. Given the importance of measuring soil moisture in situ, a network of equipment consisting of rain gauges and capacitive moisture sensors was installed in the MRR, to monitor rainfall and soil moisture in an integrated manner. The objective of this article is to understand the hydrological conditions of the soil in two high-risk areas of the MRR, built over the Barreiras Formation to set the foundations for the development of a Landslide Early Warning System (LEWS) that integrates rain and humidity. The data showed that the variation in soil moisture is very dependent on rainfall and presents sudden variations in moisture with increasing hourly rainfall. The data also revealed that the monitored soils remained wet for approximately six months in the year 2022, highlighting the potential for moderate rainfall during this period to trigger landslides.

Resumo em Inglês:

Abstract This paper presents a scoping review on the use of digital technologies for predicting, mapping, or continuously monitoring landslides on natural slopes. Articles and reviews published between 2001 and 2023 indexed by Scopus (Elsevier) were selected. The results showed that the number of publications involving this theme has been growing every year, with two periods of prominence: 2008-2010 and 2015-2021. China, Italy, India, USA and Taiwan are the five countries that published the most on the subject during the studied period. It was also found that remote sensing tools were the most used and showed strong stability, accompanied by artificial intelligence tools. Digital sensors have been widely used in Early Warning Systems, composing Wireless Sensors Network, monitoring terrain or climate variables. There is no doubt that digital technologies are extremely advantageous in relation to traditional technologies and that they already present themselves as a solution and confirm their trend of future consolidation.

Resumo em Inglês:

Abstract Interferometry is a technique that can be applied to SAR (Synthetic Aperture Radar) images that allow obtaining Digital Elevation Models, displacement measurements and assistance for monitoring large areas and/or engineering constructions. The objective of this paper is to present aspects related to the technique of Interferometry SAR (InSAR) applied to the monitoring of slopes. To do so, a systematic bibliographical review was used, through research platforms in scientific collections, in order to highlight the functioning and method of operation of InSAR. Besides that, the practical experience of the authors contributed to a critical analysis of the remote sensing technique addressed. The results show theoretical aspects related to the operation of SARs on board satellites, highlighting their characteristics, orbital systems, types of imaging geometry, as well as the principles of interferometric processing of SAR images. Practical applications demonstrate the potential of InSAR with an emphasis on slope monitoring, highlighting its ability to acquire topographic information on a millimeter scale, monitoring the long-term temporal evolution of displacements, the possibility of composing a monitoring system allowing directing the implementation of other instruments for evaluating the in situ conditions and some limitations regarding the time interval (satellite revisit time) for the acquisition of the displacement data.