Resumo em Inglês:

Abstract Phenomena that do not obey Terzaghi’s principle of effective stress (PES) are related to strain rate and time effects. This issue led the author to refer to early articles in soil mechanics, which used to consider the shear resistance of clays as a combination of two components: a frictional and a viscous one. In these articles the viscous component was assigned to the distortion of highly viscous adsorbed water layer in the contact points between grains along the plane where shearing takes place. Assuming the shear resistance of plastic soils comprises frictional and viscous resistance components, a shear stress equation can be added to the PES. It is shown that Mohr’s circle of effective stress is the sum of two ellipses: the viscosity and the friction ellipses. The ordinates of the viscosity and the friction ellipses represent the viscous and the frictional components of shear resistance in different planes, respectively. This approach leads to a failure criterion considering strain rate, according to which failure takes place whenever the friction ellipse touches the strength envelope, which is the ϕe' sloped straight line passing through the origin, ϕe' being the Hvorslev’s true angle of friction. By adding such shear stress equation to the PES, a model that explains strain rate and time effects is developed. Predictions of the proposed model are compared to results from tests carried out on San Francisco Bay Mud specimens.

Resumo em Inglês:

Abstract Limited availability of simple yet adequately validated tools for estimating the deformation potential of municipal solid waste (MSW) material poses difficulty in planning and managing landfill operations. Estimation of settlement of MSW landfills has remained a challenge because of heterogeneity and time-varying mechanical behavior of MSW materials and difficulty of extracting representative samples and reconstituting them for laboratory testing. An empirical correlation is proposed here for estimating the short-term settlement of landfill materials. The relationship was developed by calibrating laboratory data from axial (1D) compression and consolidated drained triaxial tests against field-measured shear wave velocities from five landfill sites with varied waste compositions. The correlation was validated against three full scale load tests; one obtained in this research and two reported by others, and a field compaction study from a fourth landfill. Although the proposed correlation was more accurate than an alternative developed earlier, overall it underestimated settlements by about 12%. The proposed relationship could therefore provide a conservative guidance in MSW landfill design and operation.

Resumo em Inglês:

Abstract This research shows that brackish water increases the unconfined compressive strength of swelling soil/sugarcane bagasse ash (SCBA)/lime blends. Therefore, brackish water may substitute tap water in soil stabilization. Sodium chloride (NaCl) has been used in lime-ashes-soil treatments. In northeast Brazil, swelling soils are usual and artesian wells sometimes provide brackish water containing NaCl. Northeast Brazil also has a strong sugar and ethanol industry producing sugarcane bagasse ash (SCBA) as a byproduct. Therefore, brackish water can be used in soil-SCBA-lime stabilization. Hence, this work aims to evaluate the use of brackish water as a substitute for tap water in swelling soil-SCBA-lime blends stabilization. Two series of unconfined compression tests were carried out: one with tap water and the other with brackish water. In each group, the lime content varied from 4% to 8%, and the dry density from 13 kN/m3 to 15 kN/m3. All tests were carried out with a swelling soil-SCBA proportion of 75/25 and a water content of 22%. Results have shown that increasing lime content or dry density or using brackish water allowed to increase unconfined compression strength of swelling soil-SCBA-lime blends. The porosity/volumetric content of lime index (η/Liv) was suitable to predict the unconfined compressive strength of swelling soil-SCBA-lime blends, no matter if tap or brackish water was used in the molding process. Thus, brackish can be a feasible substitute for tap water in swelling soil-SCBA-lime stabilization, increasing blends unconfined compression strength, and preserving tap water, a scarce asset in Northeast Brazil.

Resumo em Inglês:

Abstract The electrokinetic process seems to be interesting to the earthwork portion on the construction of buildings, and transportation projects since this simple, fast, yet reliable technique could expedite dehydrating of soil and reduce delays in the construction schedule. This paper examined the technical feasibility and a brief cost analysis of using plastic electrodes for electrokinetically dehydrating clayey soils with high moisture content were also carried out. The results from the experimental program carried out on a marine clayey soil with copper and plastic electrodes showed a great deal of soil improvement since positive changes in undrained shear strength occur due to the free water dehydration process induced by electro-osmosis and to the adsorbed water dehydration process induced by electromigration. It was also observed that values of the undrained shear strength remained stable at the final stages of the electrokinetic process indicating a permanent soil improvement. Finally, it was noticed that dehydrating could be achieved at lower costs by employing plastic electrodes.

Resumo em Inglês:

Abstract The geomechanical behavior of a salt rock cavern was studied using Brazilian geotechnical properties. To design the finite element model, it was necessary to implement, using Fortran language, a constitutive model representing the creep behavior, since the model used is not native to the program. The constitutive model implemented was the Multiple Deformation Mechanism Model. This model was chosen for being a robust model that represents the primary and secondary phases of creep and presents good agreement with the Brazilian salt rocks. The analyzes considered a period of 50 years after the mine closure and five internal pressures acting in the analyzed cave. The pressures considered correspond to 40%, 50%, 60%, 70% and 80% of the vertical stress at the top of the mine. The creep and dilation behaviors were analyzed, and the creep deformations obtained in the simulations was acceptable in relation to the failure criterion adopted in this paper. However, only the design of experiment that considered the two biggest internal pressure resulted in a permissible micro-crack ratio value.

Resumo em Inglês:

Abstract The performance of the subgrade towards the main deterioration mechanisms must be considered in the pavement structure design. Thus, this paper discusses the resilient modulus and permanent deformation evaluation of a pedological horizon of a Brazilian lateritic soil deposit, comparing samples compacted in the laboratory at the three compaction energies (standard, intermediate and modified) and undisturbed samples. Physical, chemical, and mechanical characterization tests were conducted. The cyclic tests were performed in repeated load triaxial tests and according to the current Brazilian standards. Five mathematical models widely used were employed to verify the resilient modulus behavior of the sample conditions, in which the Compound and Universal models showed the best correlations. For permanent deformation, the model was used, which well-expressed the plastic behavior of the analyzed conditions. Although all cases appeared to attend the shakedown criteria, some samples did not reach the deformation rate required by the standard. As the compaction energy was increased, the resilient modulus increased, and the permanent deformation decreased. Therefore, there is a substantial modification of the material behavior by increasing the compaction.

Resumo em Inglês:

Abstract Every year, millions of tons of phosphogypsum, a by-product of the fertilizer industry, are produced worldwide. As just a small part of this amount is reused, this study analyzed a new alternative to reuse this material in geotechnical works, in mixtures with lateritic soil and bentonite for the construction of liners for sanitary landfills. Four compositions were tested: 100% soil, 10% phosphogypsum + 90% soil, 10% phosphogypsum + 3% bentonite + 87% soil and 10% phosphogypsum + 6% bentonite + 84% soil. X-ray diffraction and scanning electron microscopy were used to analyze the mineralogy, while the hydromechanical performance was evaluated through compaction, hydraulic conductivity, and unconfined compressive tests. Modified free swell tests and modified Atterberg limits were used to test compatibility with NaCl, NaOH and ethanol. A solubilization test was carried out to investigate the presence of inorganic contaminants in the phosphogypsum. The addition of phosphogypsum increased the optimum water content in the compaction curves, did not change the hydraulic conductivity and decreased the unconfined compressive strength of the mixtures. The addition of bentonite increased the optimum water content, reduced the hydraulic conductivity, and increased the unconfined compressive strength. The possibility of dissolution of gypsite (main component of phosphogypsum), the problems that may arise from the interaction with chemical products, and the risk of manganese release in the subsoil lead to the conclusion that phosphogypsum is not suitable to be used in liners. However, soil-bentonite-phosphogypsum mixtures were considered eligible materials to be used in impermeable layers of other geotechnical works.

Resumo em Inglês:

Abstract This paper focuses on the use of the agglomerate technique to simulate crushable particles in the Discrete Element Method. A novel approach is proposed to design a Weibullian agglomerate by mimicking flaws within the crushable particle. The particle is designed with a constant number of sub-spheres in contrast to the approach widely used in the literature. However, the adhesion bonds between sub-spheres within the particle are selected randomly from a normal distribution. The normal distribution is designed to generate negative adhesion values, which are replaced by zero adhesion to mimic flaws within the particle. It is shown that the particle designed in this fashion exhibits a tensile strength that follows the Weibull probability function. This includes the effect of particle size that is remarkably captured quantitatively. Finally, a simple method is proposed to derive the parameters of the adhesion normal distribution from the Weibull parameters determined experimentally on single particle diametral compression tests.

Resumo em Inglês:

Abstract This article evaluates the resilient modulus and permanent deformation of granular materials of different lithological origins widely used as a pavements base layer in south Brazil. For this, a single particle size distribution was determined for the materials that were subjected to physical, chemical, mechanical characterizations, especially resilient modulus and permanent deformation by repeated load triaxial tests. It was noticed that the denser materials had a higher resilient modulus generated by increase in the sample's stiffness. For permanent deformation this tendency has not been maintained for all materials. Therefore, the granulation and structure of the materials can influence long-term tests. The Guimarães’ model has proven to be adequate for the sample evaluation. For the shakedown research, samples showed accommodation and creep shakedown. The samples that presented accommodation had an increase in the resilient modulus after permanent deformation, while those that presented creep increased or decreased resilient modulus according to the material origin.

Resumo em Inglês:

Abstract Anthropic slopes are common in constructing embankments and earth dams and forming open pit mines and fills, among others. However, these slopes artificially built sometimes could fail due to the variability of the soils, lack of expertise in determining the design parameters, and lack of knowledge of the soil's true behavior and construction methods, among others. To address these problems, physical models were made in a geotechnical centrifuge with similar characteristics to study the effect of variability. Subsequently, Monte Carlo simulations were performed using finite element models (FEM) with random geotechnical parameters for an elastic model with Mohr-Coulomb failure criteria. From these simulations, the influence of geotechnical parameters on the factor of safety and deformations was observed. The results show that the coefficient of variation obtained for the factor of safety was less than the coefficient of variation of the geotechnical parameters taken into account. This means that the coefficient of variation of the factor of safety is not the sum or the average of the coefficients of variation taken in the analysis. However, when the factor of safety is more or less constant, but the coefficient of variation of the parameters increases, the probability of failure may increase. This shows that a slope with a factor of safety greater than one can have a high probability of failure. In addition, low friction angle and low cohesion values tend to present more significant slope crest displacements.

Resumo em Inglês:

Abstract Across countries, associations and institutions publish technical standards for railway ballast, however it is observed that those norms have differences when compared to each other. Each one of them has its particularity, varying according to the stone materials available in their countries, axle load and climate. In that sense, it is still a challenge to establish specific guidelines for the properties of the ballast layer. Recently, several techniques for acquisition, image analysis and particle scanning have been developed, either in 2D or in 3D. Those techniques vary from the use of pachymeter to the use of sophisticated scanners. This research seeks to evaluate, through laboratory tests, the evolution of the particle shape parameters through 3D scanning and the level of degradation of the steel slag when subjected to stresses close to those experienced in freight transport railways. Based on the performed tests and the obtained results, the authors recommend for a railway pavement subjected to a load of 32.5 t/axle and composed of steel aggregates used as ballast, a granulometric distribution with uniformity coefficient 1.5 ≤ Cu ≤ 1.6 (AREMA n. 4) and particles with: 0.625 ≤ Elongation ≤ 0.999, 0.567 ≤ Flatness ≤ 0.995, 0.475 ≤ Aspect ≤ 0.969 and 0.825 ≤ Ellipsoidness ≤ 0.957. These specifications enable a good performance of the ballast layer. In addition, the results found contribute to the understanding of siderurgic aggregate behavior under cyclic loading conditions.

Resumo em Inglês:

Abstract Geotextile tubes can be used to dewater materials such as sludge, sediments or residues aiming at reducing their moisture contents to acceptable levels. The tube filling process can be carried out using one or several filling stages, and the number of stages can influence the tube behaviour in terms of dewatering rate, final shape and geotextile strains, for instance. In this research, laboratory tests were carried out on nonwoven geotextile tubes for the dewatering of a fine-grained material using different numbers of filling stages. The behaviour of the tube was monitored by instrumentation to assess tube geometry, pore pressures, total stresses at the tube base, geotextile strains and retention capacity. Evaluations of the accuracy of some available methods for the prediction of tube behaviour were also made. The results obtained showed that the increase in the number of filling stages resulted in larger final tube height, volume, geotextile strains as well as larger diameters of the soil particles that piped through the geotextile. Predictions of tube behaviour by available methods showed varying degrees of accuracy depending on the tube parameter considered.

Resumo em Inglês:

Abstract The characterization of unsaturated soils using hydromechanical methods is an essential requirement in soil science. However, current laboratory techniques used to obtain soil water retention and unsaturated hydraulic conductivity curves are time-consuming. To address this issue, a method based on indirect measures (electrical resistivity/electrical conductivity) was developed to quantitatively characterize soils. A novel unsaturated semi-empirical hydrogeophysical model of soils was developed by incorporating the hydrodynamic, geophysical, and petrophysical characteristics of soils. The model assumes that the parameters influencing the variation in the volumetric water content with matric suction and electrical resistivity are the same. The electrical resistivity characteristic curve (ERCC) defines a function that correlates environmental variables, electrical resistivity, soil water status, matric suction, hydraulic and petrophysical parameters, and fluid electrical resistivity. Model validation confirmed that the proposed approach can estimate the soil water retention curve (SWRC) via the indirect measures, and the results agreed with the experimental data. This indicates that it is possible to determine the SWRC and unsaturated hydraulic conductivity function of soil using the described approach.

Resumo em Inglês:

Abstract It is common to observe residences with a high number of pathologies related to differential settlements in the municipality of Cruz Alta, Rio Grande do Sul, Brazil. Motivated by this perspective the first Geotechnical Engineering Experimental Field was implemented in the municipality. Standard penetration test and cone penetration test was conducted to characterize the subsoil and execute 17 excavated piles: nine compression piles and eight reaction piles. This technical note presents and discusses the results of the geotechnical load capacity obtained with the static load test in three different pile conditions: conventional piles, floating piles, and reinforced piles by inserting a crushed stone layer compacted at the bottom of the drilling. The piles evaluated have a length of 3 m and a diameter of 30 cm. The piles are immersed in a layer of unsaturated laterite soil. Conventional piles are extensively executed in the municipality due to the limited equipment of the companies offering this service. In summary, the piles presented low bearing capacity, however, the reinforced piles proved to be a viable alternative in terms of increased resistance. The conventional piles presented low load capacity and significant settlements. The insertion of the reinforcement at the tip of the pile resulted in a resistance gain in the range of 31%. The study of floating piles was important to understand the behavior of the pile base. This technical note will enable the geotechnical understanding for future researchers or designers who will work with this soil condition in the state of Rio Grande do Sul, Brazil.

Resumo em Inglês:

Abstract Fiber-reinforcement has been reported as an effective and cost-attractive technique to improve the mechanical behavior of cemented soils. However, the dosage methodologies for these mixtures are still limited, especially regarding dynamic loading. The objective of this research was to analyze the dynamic response and strength behavior of fiber-reinforced cement-treated sand. In this sense, fatigue life, unconfined compressive strength, and split tensile strength tests were conducted. Results indicated that the mechanical behavior of the soil-cement mixtures was governed by fiber content, cement content and void ratio. The presence of fibers, the increase in cement content and the decrease in void ratio improved the overall mechanical behavior of all specimens. The porosity/cement content index resulted in a viable dosage method to predict both the monotonic and cyclic behavior of the mixtures. Lastly, the statistical analysis of variance corroborated the experimentally observed findings.

Resumo em Inglês:

Abstract Geophysical methods are potent tools for geotechnical site characterization in a non-destructive way. They improve the extrapolation of punctual data from direct survey methods, allowing a fast and cost-effective evaluation of large areas. Ground Penetrating Radar (GPR) and DC electrical resistivity (ER) are the most requested methods for geotechnical and geoenvironmental applications. Their use, however, is usually uncoupled, with no sharing of information from one method to another to improve data interpretation. This case study illustrates the development of protocols and scripts in R© programming language for ER and GPR data analysis with Standard Penetration Tests (SPT) data to produce more accurate information on subsurface conditions concerning lithology, water content, and groundwater table (GWT) position. The SPT data were used to associate resistivity ranges with different soil lithologies and GPR pulse velocities for estimating the soil water content. Estimated water content values aided in interpreting ER data and locating the groundwater table. The contacts between layers in the radargrams allowed the refinement of the ER model, rendering 3D volumes for each soil layer in situ.

Resumo em Inglês:

Abstract This is an investigative work by the authors, all of them former students and employees at Tecnosolo Ltd, the company founded by our late Professor Costa Nunes, to find and photograph the first tieback wall designed and built in 1957 by Tecnoloso under Prof Costa Nunes’ guidance.

Resumo em Inglês:

Abstract Predicting the pile’s load capacity is one of the first steps of foundation engineering design. In geotechnical engineering, there are different ways of predicting soil resistance, which is one of the main parameters. The pile load test is the most accurate method to predict bearing capacity in foundations, as it is the most accurate due to the nature of the experiment. On the other hand, it is an expensive test, and time-consuming. Over the years, semi-empirical methods have played an important role in this matter. Initially, many proposed methods were based on linear regressions. Those are still mainly used, but recently the use of a new method has gained popularity in Geotechnics: Artificial Neural Network. Over the past few decades, Machine Learning has proven to be a very promising technique in the field, due to the complexity and variability of material and properties of soils. Considering that, this work has reviewed and mapped the literature of the main papers published in journals over the last decades. The aim of this paper was to determine the main methods used and lacks that can be fulfilled in future research. Among the results, the bibliometric and protocol aiming questions such as types of piles, tests, statistic methods, and characteristics inherent to the data, indicated a lack of works in helical piles and instrumented pile load tests results, dividing point and shaft resistance.

Resumo em Inglês:

Abstract The use of geosynthetic clay liners (GCLs) as a hydraulic barrier for contaminants containment has proved to be an efficient alternative for the soil and groundwater protection. This geocomposite can be used in engineering systems to contain accidental spills and leaks of fuel in distribution centers, reservoirs and resulting from transport, where the geosynthetic acts as a protection against subsoil contamination. However, there is a concern about the behavior of GCLs in the face of these contaminants about possible changes in their properties, in order to compromise the retention capacity and permeability of the material. In this regard, the present work aimed to carry out a systemic and bibliometric study of publications related to the hydraulic conductivity of GCLs after contact with some type of fuel, available in the Scopus database (Elsevier) and Web of Science (Clarivate). The primary data selected directly from the databases were analyzed, making it possible to filter the publications that made up the bibliographic portfolio of the research, resulting in 14 selected documents, which were synthesized, and the main points were highlighted. From the bibliographic portfolio, bibliometric indexes of scientific production were created, as well as the temporal distribution of publications, authors, countries, and scientific journals that most contribute to the theme and the terms most evidenced in the documents. The panorama observed through bibliometrics was that it is a very recent theme, which still has a lack of scientific production, revealing itself as a promising area for the development of research.