Abstract in English:

Abstract The paper reviews the published literature on some aspects of fabric and particle behaviour in cohesionless soils. It uses insights from Discrete Element Modelling and Microcomputed Tomography to speculate on reasons for the difference in behaviour observed between moist tamped and sedimented sands at the same global void ratio and stress state. It is suggested that inhomogeneities in the form of macrovoids in moist tamped samples trigger localisation, collapse and the development of a local scale chain reaction. It questions whether a similar sequence applies at the field scale and whether expansive partial drainage influences the rate of propagation of the chain reaction. The paper offers reasons why the use of critical state based on moist tamped samples to assess the stability of tailings, may not be the best approach, and suggests that identifying instability lines for sedimented samples at appropriate void ratios and principal stress directions, may be preferable. Critical state reflects behaviour at large strains where initial and evolving inhomogeneities affect identification of relevant void ratios; instability lines reflect behaviour at small strains where inhomogeneities probably initiate collapse. The paper emphasises the importance of spatial variations in local void ratios in loose material, the importance of anisotropy of collapse potential and of load-controlled rather that strain-controlled shearing.

Abstract in English:

Abstract In this work we evaluate the physical-mechanical behavior of lateritic soil with addition of carbon nanotubes. The soil was collected in a commercial deposit located in Rio Branco – AC and later characterized through particle size tests, X-Ray Diffraction, X-Ray Dispersion Spectroscopy and Tropical Compressed Miniature essay. The dispersion of nanotubes in solution was carried out and the size of the nanoparticles was verified using Dynamic Light Spreading - DLS, Zeta Potential and PDI. Three percentages of additions (0.05%, 0.1% and 0.2%) of carbon nanotubes were evaluated and compared with the control group according to the parameters of Atterberg limits, real density, dry density maximum and optimum humidity. The results indicate that the soil has a clayey behavior with a medium texture, with the presence of clay mineral kaolinite in its composition and silicon and iron oxides. The dispersion of carbon nanotubes reached particles with an average hydrodynamic diameter of 68.9 nm and Zeta Potential of -24.87 mV and PDI of 0.231, characterizing a solution as moderately dispersed and kinetically stable. The results of the liquidity limit and plasticity tests showed a reduction of 10 and 13%, respectively, with the addition of carbon nanotubes, while for the parameters of plasticity index, real specific mass, maximum dry density and optimal moisture, they did not show significant variation. Carbon nanotubes interact with soils with lateritic behavior, and further studies are essential to better understand the mechanisms behind this interaction.

Abstract in English:

Abstract Dispersivity is a severe pathology that occurs mainly in clay soils and is usually catastrophic in geotechnical structures susceptible to this damage. Hundreds of dams worldwide have failed due to quality problems, mainly by piping in the body, foundation, spillway, culvert, and other peripheral structures. The pinhole test is currently considered the most accurate test for detecting the dispersivity of clay soils. However, it presents problems when objectively evaluating the dispersivity of a material due to the qualitative nature of the estimation of results. In particular, the methodology for determining turbidity has been identified. This document studies different piping paths in the sample, which a priori may be more realistic than the single path in the current test. A kaolinitic clay, widely studied through index and mineralogical tests, is used as the base material. Regarding the detection of dispersivity, a specialized test package was used to reduce the uncertainty of the results. Natural samples were analyzed using ASTM D4647-13. A modification of the pinhole test was proposed based on the imposition of additional artificial channels. The results revealed that this modification can make the test more realistic because when the dispersive front advances in the soil, it does not travel along a single path but instead looks for different erosive paths. The details of this assertion are discussed throughout the paper.

Abstract in English:

Abstract Recycled construction and demolition waste (RCDW) has demonstrated geotechnical properties that encourage it to be used in reinforced soil structures (RSS) with geosynthetics. However, the interaction between RCDW and reinforcements needs to be better understood, given its importance for design. This paper presents a qualitative study on the interaction between geogrid and recycled sands by means of pull-out tests performed on small equipment. Tests with the same degree of compaction and a geogrid buried in different types of recycled and natural sands (for comparison purposes) were performed. The characterisation of the materials was carried out in the laboratory and the variability of their geotechnical properties was evaluated. In addition, fill material moisture content was investigated as another potential factor influencing soil-geogrid interface shear. The results of the pull-out tests demonstrated the specific influences of the factors investigated. The comparative study showed that recycled sands can be suitable materials to be used as backfill in geosynthetic reinforced soil structures, meeting physical, mechanical and environmental requirements for this kind of work.

Abstract in English:

Abstract Expansive soils can cause large-scale damage to the infrastructure. Soil stabilization with Portland cement and lime has been widely utilized as a solution to this problem. However, these stabilizers are non-renewable and energy-intensive. Alkali-activated binders are alternatives with lower carbon dioxide emissions. This research evaluated an expansive soil stabilization with an alkali-activated binder produced from sugarcane bagasse ash (SCBA), hydrated eggshell lime (HEL) and sodium hydroxide (NaOH). Free-swelling tests alongside a statistical analysis evaluated the influence of dry unit weight (12.5 and 14.5 kN/m3), binder (4 and 10%) and moisture content (19.7 and 24.7%) and curing time (0 and 7 days) on the stabilized mixtures. A four factors factorial design with duplicates and central points was outlined. To better understand the NaOH and SCBA influence over the soil expansion additional tests were performed. In general, an increase on the studied factors reduced swelling, especially binder content. However, the alkali-activated cement presented no clear correlation between higher density and higher expansion. Swell reduced from 13.8% (12.5 kN/m3 and 19.7% moisture) and 8.8% (12.5 kN/m3 and 24.7% moisture) to 2.5% and 0%, respectively, after 7 days and 10% binder addition for the alkaline cement. For Portland cement, swell reduced from 13.8% (10.2 kN/m3 and 22.5% moisture) and 12.5% (10.2 kN/m3 and 27.5% moisture) to 1.8% and 1%, respectively, after 7 days and 4% binder addition. Samples containing NaOH expanded less than samples molded with only water. Finally, the alternative binder might be a viable option to replace Portland cement for expansion control.

Abstract in English:

Abstract The theory of homogenization of differential equations has become an open field of research in several areas of the exact sciences and has proved to be a powerful tool for understanding the global behavior of heterogeneous materials. Despite knowing that the deduction of Darcy's law through the Navier-Stokes equations has been debated for decades, many questions remain open, mainly regarding more complex boundary conditions, cases involving multiphase flows and the numerical homogenization techniques. It is known today that Darcy's law is presented in the form of a linear relationship only for a range of hydraulic gradient and that this range overlaps the range of laminar flow through soil voids. Therefore, it is proposed in this work to understand the loss of linearity in Darcy's law, based on the theory of homogenization, modifying and exploring the limit results obtained by Allaire in 1991.

Abstract in English:

Abstract The inclinometer probe is used to measure angle variations along a soil profile. These variations can be transformed into horizontal displacements along the profile depth, enabling the understanding of the deformation of geotechnical structures (e.g., tailings dams, embankment dams, rockfill dams, and excavations) and natural slopes. Such knowledge can guide preventive and corrective actions and mitigation measures to reduce the severity of socioeconomic and environmental impacts. In this study, a low-cost, reduced-dimension inclinometer probe was developed and validated. Accessible technologies (MEMS inclinometer sensor, microprocessor, logic level converters, communication module, and other electronic components) were used for the probe. The sensor reading programming was developed using Python language and interpreted using an Excel spreadsheet. The probe was calibrated on a three-dimensional measurement table with the aid of a mechanical device to stabilize its inclination and validated by comparison of its output with those of a commercial probe. The probe had a lower cost than commercial probes and generated similar readings, although the reading time was longer due to the increased number of measurements required.

Abstract in English:

Abstract The West-East Integration Railway (Ferrovia de Integração Oeste-Leste -FIOL) is an infrastructure project designed to integrate and promote the socio-economic development of the Northeast region of Brazil. In countries with heavy-haul railway operations, there has been increased demand for ballast materials that can withstand cyclic loading of up to 40 tons per axle. In this context, in order to achieve greatest operational efficiency, it is essential to evaluate the characteristics of the limestone aggregate to be used in the ballast layer, as well as the level of cyclic stress that the ballast can withstand. The laboratory investigation consisted of characterization tests, single particle crushing tests, monotonic triaxial tests, and evaluation of the morphological properties of the particles using the Aggregate Image Measurement System. This paper introduces the equipment, describes the experimental procedures, outlines the specimen preparation, and presents the experimental results. The purpose of the study is to estimate the long-term behavior of ballast based on monotonic triaxial tests, the shakedown phenomenon, and the cyclic stress ratio. The results suggest that the cyclic stresses commonly observed in heavy-haul railways may exceed the cyclic stress ratio compatible with the shakedown regime, resulting in a progressive plastic creep regime. Furthermore, the quantity of non-cubic particles exceeds the limits set forth in international ballast standards necessitating a rigorous assessment of the particle shape prior to use in the field.

Abstract in English:

Abstract Thin spray-on liners (TSLs) are a promising rock support method due to their ease of application and versatility. However, their effectiveness relies on experience and lacks a complete scientific understanding. To bridge some of the knowledge gaps existing in support mechanisms, this study investigated the effect of different parameters on the shear-bond strength of TSLs as a surface support in underground excavations. The parameters included liner thickness, curing period, material type and surface cleanliness. A polymer based cementitious TSL was utilized while the material type included quartz and sandstone rocks and 30 MPa concrete. Liner thicknesses included 16.2 mm, 20.2 mm, 24.2 mm, 28.2 mm, and 32.2 mm while curing periods were 7 days, 14 days, and 28 days. It was observed that the TSL shear-bond strength varied with different materials. Quartz with the lowest porosity had the lowermost shear-bond strength at all liner thicknesses and curing periods. The shear-bond strength improved with liner thickness up to 24.2 mm and then decreased up to 32.2 mm due to the optimum thickness effect. It also increased with curing period. Oil reduced the shear-bond strength for all the material types at all liner thicknesses and curing periods.

Abstract in English:

Abstract Although fully penetrating stone columns have widely been studied in the literature, the number of published studies on floating stone columns – which also have been efficiently used to improve vertically lengthy soft-clay deposits – is very limited. Basal reinforcement with geosynthetic is another technique that increases overall stability of embankments on soft soils and can be combined with stone columns. In the paper, mechanical-hydraulic coupled finite element analyses are performed to study a floating stone column-supported embankment on a thick soft soil deposit. A parametric analysis is conducted so that the influence of two governing factors is evaluated: length of stone columns; basal reinforcement with geosynthetic. An overall stability analysis method, which uses the results of finite element analyses, is also applied. Results of several key variables are analysed: overall safety factor, settlements, horizontal displacements, vertical stress at the embankment base, stress concentration ratio, excess pore pressures and geosynthetic tensile force.

Abstract in English:

Abstract Iron ore tailings dams must be constantly monitored for safety purposes. Among the aspects traditionally monitored are geotechnical protocols, such as piezometric levels along the dam. Recently, geophysics, a science that studies, among other things, dynamic processes in the Earth, has contributed to non-invasive monitoring using electro-resistivity methods. Geophysical methods provide a large amount of data in relatively quick samples, but there is little information on the integration of traditional geotechnical and geophysical techniques. Therefore, this work aimed to evaluate the relationship between geophysical data, monitored every 15 days between May 2022 and March 2023, and geotechnical data from an iron ore tailings dam located in the Iron Quadrangle. The geophysical method used was two-dimensional electrical imaging with a Schlumberger array. Analysis of variance and multiple regression allowed us to evaluate the relationship between resistivity values, piezometer level, sampling time, and rainfall. Piezometry data explained the electro-resistivity significantly, while sampling time and rainfall did not significantly explain electro-resistivity. Therefore, the dam's electro-resistivity patterns have not changed significantly over the period, and local rainfall does not imply an immediate response in resistivity. These conclusions can support new directions in decisions about monitoring iron ore tailings dams and may contribute to advances in dam safety in the mining sector.

Abstract in English:

Abstract This study presents a laboratory investigation on the susceptibility of suffusion in soil samples collected from a very old earth dam. The dam, rebuilt around 1800, is composed of two earth fills and lacks a clay core or filtration components, making it vulnerable to internal erosion. Following an inspection in 2006, concerns were raised about the dam's vulnerability to internal erosion during strong floods. Boreholes and vibro-cores were performed to collect samples, which were then tested for suffusion susceptibility. The study found that four out of six samples were highly susceptible to suffusion erosion, with the erosion process starting at gradients much lower than unity. The opposite was observed for samples with fines content greater than 30% and showing some plasticity. The results were compared to predictions from seven geometric criteria found in the literature, but none of the methods could forecast the behaviour of all tests. The study highlights the need for laboratory tests when there is no agreement between the predictions from available criteria. The findings of this study were used to inform the rehabilitation of the dam, which included installing sand filters designed to capture the smallest particles and relief wells distributed along the entire length and height of the eastern embankment. The study demonstrates the importance of assessing suffusion susceptibility in embankment dam safety control and the need for laboratory tests to validate predictions from geometric criteria.

Abstract in English:

Abstract Large quantities of scrap tires are produced by the automobile industry each year, which causes disposal challenges and impacts the environment. However, scrap tires exhibit various properties, including tensile strength, abrasion resistance, durability, thermal conductivity, elasticity, and more. Due to their versatile characteristics, these scrap tires can be utilized as construction materials for various civil engineering works to reduce their negative environmental effects and conserve natural resources. This study aims to understand the shear strength behaviours exhibited by geocell-reinforced mixtures of rubber and sand through the unconsolidated undrained triaxial test. Various parameters, including rubber sizes (425 μm to 12 mm), rubber contents (10% to 40% by volume), confining pressures (50 to 300 kPa), and geocell heights (0.2H to 0.8H, where H is the height of triaxial sample), were systematically examined to understand their impact on shear strength characteristics. The experimental findings reveal that deviatoric stress is enhanced with increasing confining pressure and rubber sizes. The maximum benefits of the rubber-sand mixture were observed at 30% rubber content. Geocell-reinforced rubber sand mixture has a higher shear strength with respect to the unreinforced mixture. Furthermore, the energy absorption capacity of the geocell-reinforced rubber sand mixtures was much better as compared to either the clean sand or rubber-sand mixture. The findings of this research demonstrate that geocell-reinforced rubber sand mixtures are suitable for various geotechnical engineering works.

Abstract in English:

Abstract Stiffness-related geometric characteristics are closely linked to the performance of structural systems. The influence of foundation stiffness on the soil-structure interaction (SSI) mechanism was investigated by numerical modeling of different building foundations. Numerical tools (PLAXIS 3D and TQS/CAD) were used for decoupling analyses of the interaction between the structural components. Results obtained from instruments installed in a building case study were used to refine the numerical calculations. Linear elastic constitutive models and beam elements were useful in reducing computational processes and ensuring study feasibility. The simulation results provided a satisfactory representation of field observations. Interaction between piles and the environment governs the relationship between foundation stiffness and uniform settlement. Rigid pile groups are achieved with greater pile length, diameter and spacing. This study highlights the different effects of pile geometric parameters on loading and unloading rates in pillars, demonstrating that the SSI mechanism is more sensitive to less rigid foundations, particularly those with greater pile embedment. It was concluded that numerical simulations to predict settlement as realistically as possible require understanding and selecting the most appropriate model and type of calculation.

Abstract in English:

Abstract Submarine debris flows are events that occur with great frequency on a geological scale and can cause major damage to offshore structures or even loss of human life. Understanding the mechanisms involved in the development of a debris flow requires not only knowledge of soil mechanics, but also knowledge of fluid mechanics, since the incorporation of water during the flow causes changes in shear strength. Unlike soils, the shear strength of fluids is represented by mathematical models called rheological models. The objective of this paper is to propose a new rheological model capable of representing the changes caused by water entrainment into a submarine debris flow, by correlating it with the Liquidity Index of the soil. A rheological analysis of marine clay samples from the pre-salt layer has made it possible to represent the variation in strength due to water content. The influence of water content and velocity on flow behavior has also been studied through the analysis of centrifuge tests performed in a previous study.

Abstract in English:

Abstract The stability of slopes or the occurrence of mass movements is directly related to the incidence of rainfall. In this work a qualitative analysis of the historical series was made for the period between May 2012 and February 2019, where the development of pore pressures was evaluated, analyzing the behaviors of the instruments, correlating their readings with precipitation and with variations in the water table. Pore pressure was measured using vibrating wire piezometers, and precipitation data was collected using pluviometers with tipper buckets, whose readings were obtained by a datalogger model ML1-FL. From the data collected, it was possible to estimate the duration of a rainfall event for the soil, as that time interval between the occurrence of rain and the dissipation of excess pore pressure. These intervals are between 3 and 26 days in duration. The main results were: the period between the end of June and August is the driest and the highest precipitation occurs from December to early June; Precipitation of up to 100 mm of daily accumulation is well distributed throughout the year and occurs in all seasons. The pore pressure values developed were low, with a maximum of 9.3 kPa for the deepest piezometer on elevation 92.40 m. There is a delay between the occurrence of precipitation and the recording of the peak pore pressure. The in-depth knowledge of variations in precipitation and pore pressure can support the development of more robust geotechnical engineering projects. This preventive approach, based on concrete data and correlations, offers a more reliable strategy for mitigating the risks associated with landslides, directly contributing to the safety and continuous operation of the BR-101/SC highway.

Abstract in English:

Abstract Dynamic probing light (DPL) is available among a wide range of dynamic penetrometers. This equipment can be used in locations where conventional sounding equipment may have limited access. Here, the shear wave velocity (Vs) determination by the downhole seismic technique is incorporated to the DPL to develop a hybrid test, the seismic DPL test, for the preliminary characterization of tropical soils. The corresponding equipment, test procedure and data interpretation of the seismic DPL (S-DPL) test are presented and discussed. S-DPL test campaigns were carried out at two experimental research sites where crosshole seismic tests were conducted to provide reference Vs profiles. The Vs profiles determined with the S-DPL test are in accordance with those determined with the crosshole test for both sites. The proposed hybrid test (S-DPL) has the potential to serve applications in preliminary site characterization, particularly at sites including unsaturated tropical soil profiles.

Abstract in English:

Abstract In recent years, two tragic accidents in Brazilian tailings dams resulted in a lack of trust in the performance of these structures. This paper aims at proposing a new procedure for estimating the liquefaction risk of existing tailings dams, with the use of well-known probabilistic methods as a valuable tool in the decision-making process for triggering an Emergency Plan. The combination of a rigorous limit equilibrium stability method (Spencer, 1967) and the FOSM probabilistic procedure (Christian et al., 1992) has proved to adequately predict the imminent liquefaction risk of both Fundão and Feijão tailings dams, which recently collapsed in Mariana (2015) and in Brumadinho (2019), both in Minas Gerais State, Brazil. Considering the triggering mechanisms known to have occurred, the estimated probabilities of liquefaction failure at the time of the accidents were 36% for Fundão Dam, and 47% for Feijão Dam. The results show that the risk associated to the collapse of both structures was well above the acceptable level suggested by current standards.

Abstract in English:

Abstract Rock and joint alteration leads to modifications in their properties, resulting in a reduction of rock mass strength and consequently a decrease in the safety of engineering structures. The alteration process changes the material and alters its geomechanical behavior. This research presents the studies conducted to evaluate the mechanical behavior of rock joints in the gneiss massifs that make up the hydraulic circuit of the Simplicio Hydroelectric Plant due to their alteration. Compilation and analysis of data from previous research were carried out to parameterize the joints at different levels of alteration. Deterministic stability analyses showed that the alteration process of gneiss joints can significantly reduce the slope safety factor by up to half of its initial value. Furthermore, probabilistic analyses revealed an increase in failure probability of approximately 10% among the studied alteration classes. The results underscore the importance of assessing the level of joint alteration in engineering projects.

Abstract in English:

Abstract This paper presents an experimental and numerical study on the behavior of three (3) instrumented caissons in a tropical laterite soil in the Planalto Central, DF, Brazil. The concrete caissons have a shaft diameter of 0.6 m, a bell diameter of 1.2 m and 1.3 m and lengths of 8.9 to 14.4 m. Static load tests were conducted out to investigate the behavior of the caissons. The results of load vs displacement and their interactions with the tropical soil were measured and evaluated using the methodology of Camapum de Carvalho et al. (2008, 2010) and numerical modeling with back-calculation of static load tests in the Plaxis 3D software. The paper presents the analysis of the load transfer lines and the comparison with the proposed methods. The results pointed to a constant load transfer along the shaft, with a significant contribution from the skin friction, developed for a fraction of the displacement necessary for its mobilization. The accuracy of using the Camapum de Carvalho et al. methodology stands out (2008, 2010), identifying the region dominated by skin friction, tip and plasticization of the foundation, confirming the authors' predictions for a tropical soil in the Distrito Federal/DF, Brazil. The numerical method using the Plaxis 3D software, proves that for the limit test load there was a significant contribution from skin friction, which must be consider in the analysis of the behaviour of caissons.