Abstract in English:

Abstract Research on the viscous behavior of soft soils suggested that the effective stress should be divided into two components. One is related to the solid contacts between the grains, and its variation would be the true cause of deformations and distortions. The other is related to the viscous contacts of the water adsorbed to the grains, which would not cause deformations or distortions, and would be a function of the strain rate. This model is able to explain some phenomena, such as secondary consolidation and the increase in pore pressure after drainage closure. However, a consolidation theory adopting a linear relationship between the viscous component and the strain rate (Newtonian behavior) could not reproduce the secondary consolidation as seen in consolidation tests. In this paper, three theories of radial flow consolidation were developed and solved analytically. In two of them the linear relationship was adopted, while in the third one a non-linear relationship was proposed (non-Newtonian behavior). The solutions showed that the linear relationship is in fact not able to reproduce secondary consolidation, but the non-linear relationship provided much better results and can be a promising tool for future studies.

Abstract in English:

Abstract The paper addresses the stability analysis of a circular tunnel face driven by a pressurized shield by means of the limit analysis kinematic approach implemented in the context of the Mohr-Coulomb strength condition. Emphasis is given to the assessment of the effects of seismic loading on the value of face support pressure that is required to prevent failure. The approach relies upon the pseudo-static method to model the destabilizing effects induced by the inertial forces associated with the passage of seismic waves in the ground. Rigorous limit analysis solutions for the limit face supporting pressure are derived from the analytical implementation of 3D and 2D failure mechanisms specifically devised for dealing with such a stability analysis problem. Indeed, original analytical expressions are provided and allow the evaluation of the pressure stabilizing the tunnel face. The accuracy of the approach predictions is assessed by comparison with available experimental and analytical results as well as with 2D finite element solutions. The influence of some relevant problem parameters in the context of tunnel face stability analysis is finally investigated, thus providing some preliminary guidelines for practical use in tunnel engineering.

Abstract in English:

Abstract The heterogeneity of microelement strength of rock particle materials is one of the main factors that cause the size effect of the rock particle crushing behavior. In this paper, a numerical model of rock particles that considering the characteristic of microscopic heterogeneous bond strength was established by using Weibull distribution theory through discrete element method. Single particle crushing experiments were carried out on five groups of rock particles and numerical particles with different particle sizes (6-21 mm), the crushing strength and failure modes of rock particles and numerical particles with different sizes were obtained. The results shows that the proposed numerical model can effectively reproduce the size effect of rock particle crushing behavior. The particle crushing strength data are satisfied the Weibull statistical model and have obvious size effect. The particle failure modes can be divided into three different failure types: “brittle” failure, “quasi brittle” failure, and “ductile” failure. As the particle size increase, the particle failure mode changes from “ductile” failure to “brittle” failure. Finally, a microscopic damage function model of particle crushing was established based on the numerical simulation results, which explained the microscopic mechanism of the size effect of particle crushing behavior. This study not only helps to improve the stability of engineering materials, but also optimizes engineering design and construction, and promotes related technological innovation.

Abstract in English:

Abstract The advent of construction informatization technologies and the success of the BIM (Building Information Modelling) methodology in the infrastructure market have increased the need for collaboration between different areas of knowledge, professionals, and agents involved in an infrastructure or civil project. For this collaboration to be effective, the correct standardization of procedures is essential to ensure efficient communication between the parties involved in these complex processes. The field of geotechnics and geotechnical investigations has the AGS (Association of Geotechnical and Geoenvironmental Specialists) standard for electronic transmission of files produced during drilling and laboratory tests. However, there is a gap regarding the standardization of a digital structure that can be used for the implementation of geotechnical databases. This paper proposes a logical model for the demands of the geotechnical market, which can be used by the entire community. The proposed model allows for easy access to large-scale data and the possibility of performing mathematical operations more easily.

Abstract in English:

Abstract This work compares the effectiveness of different biogrout agents to improve the mechanical properties (strength and stiffness) of two sandy soils. Based on the results of unconfined compressive strength tests for different curing times (3-180 days), the results obtained from microbial induced calcium carbonate precipitation using two bacteria (Sporosarcina pasteurii and Idiomarina insuliasalsae) are compared with employing urease to promote calcium carbonate precipitation and the use of the biopolymer xanthan gum (3-28 days). Additionally, the methodologies of calcite precipitation and the use of xanthan gum are also analyzed by examining scanning electron microscopy images. For a curing time of 28 days, the results show that the use of urease is the best of the three bio-based methodologies to improve sand, while the least efficient methodology is the use of the biopolymer xanthan gum. The use of both bacteria increases the unconfined compressive strength during the curing time (until 180 days); regarding the use of urease and xanthan gum, the unconfined compressive strength remains approximately constant for a curing time longer than 7-14 days. In terms of stiffness, the use of the bacteria Idiomarina insuliasalsae and urease result in a better improvement, while the use of the bacteria Sporosarcina pasteurii and xanthan gum has only a marginal effect on the stiffness.

Abstract in English:

Abstract This work uses a new cementitious agent composed of porcelain polishing waste and hydrated lime in the mitigation of static liquefaction in a loose dune sand. The undrained behavior of the soil was investigated in 16 triaxial tests under four confining stresses (50, 100, 200 and 400 kPa), on loose samples (relative density of 25%) compacted with two levels of waste (10% and 30%) and lime contents (3% and 7%) cured at 28 days. Stress-strain behavior, ultimate strength and critical state parameters were evaluated. The results showed a brittle response of the stabilized sands, dilatant tendency and low liquefaction potential, however, the behavior changes with the increase in the confining stress. A friction angle of up to 42.6° and a cohesion intercept of up to 108.1 kPa were found for the stabilized sand. When compared to the pure sand, stabilization caused an increase in strength, of up to 17 times, and in brittleness with a change from contractive to dilatant behavior. For tests up to 200 kPa, the liquefaction potential reduced to values below zero. Therefore, the cementation of the grains by using porcelain polishing waste and hydrated lime was efficient in mitigating the static liquefaction potential of the dune sand.

Abstract in English:

Abstract Mohr’s circle is a convenient geometric method to solve two-dimensional stress and strain problems in geotechnical engineering and materials engineering. The pole point is such a special point that can help readily find stresses and strains on any specified plane by using a diagram instead of complex computations. This paper first presents two conventional pole point methods of a Mohr’s strain circle, i.e., the parallel line method and the normal line method. A new method of determining the pole point of strain, called the ray method, is then proposed. It was found that the parallel line method and the normal line method are two special cases of the ray method; however, the parallel line method was proved the most efficient way to determine the strains for a specified plane. The uniqueness of the pole point was proved by using an indirect proof; and the pole point method was verified by a theoretical method. Results also show that Mohr’s strain and stress circles can be drawn in a concentric circle. Based on the relationship between the pole points of stress and strain, any relatively complex stress and strain states can be determined by using the pole point method rather than using the theoretical method.

Abstract in English:

Abstract Energy geostructures are a cost-effective solution for low enthalpy geothermal installations. Heat exchanger pipes are attached to the reinforcing cages of geotechnical structures to combine structural and geothermal roles. However, the installation of a group of multiple energy structures, such as a pile group, can lead to a heat cluster effect, which tends to decrease the efficiency of the heat pump (COP factor). This phenomenon is amplified by the number of grouped energy geostructures. However, energy geostructures are often installed in areas with groundwater flow. This induces a thermal washing effect, which decreases the risk of multi-year thermal shifts and preserves heat pump efficiency. In this paper, we evaluate the heat cluster effect in a group of piles, its influence on heat pump COP, the benefit of thermal washing due to underground water flow, and the effect of various seasonal scenarios. For this purpose, we present and use a specific numerical process that allows for modeling energy geostructure installations and interactions between groundwater flow models and thermal models. The heat pump COP is then estimated according to variable heat load, which depends on soil temperature.

Abstract in English:

Abstract A subject of great relevance for geotechnical engineering is the search for economical solutions to improve soil mechanical characteristics. Due to the constant evolution of the industry and the regular launching of new products – developed to compensate for various soil deficiencies - the need for applied research continually arises. Geosynthetics are reinforcement materials that increase soil strength and its traction features. Among them, microgrids have been used as a separating element for distinct materials, but studies on microgrids as reinforcement materials are still not quite common in the literature. This research aimed to evaluate on a small scale the mechanical behavior of microgrids as reinforcement materials in sandy soils by analyzing the strength parameters obtained through consolidated-drained triaxial tests (CD) of specimens with none to 3 layers of the material. The study also compared the performance of sandy soil reinforced with microgrid and non-woven geotextiles of different weights (200 g/m2 and 300 g/m2). Results showed that the insertion of microgrid layers in sandy soils increased the strength parameters, and the behavior of reinforced soil has changed from strain-softening to strain-hardening. The sample reinforced with one layer of microgrid had improved cohesion and friction angle compared to samples with one layer of non-woven geotextiles.

Abstract in English:

Abstract The inadequate disposal of rubber waste from scrap tires is a globally recognized problem. In Brazil alone, 12.23 million tires were manufactured in the first quarter of 2024. The incorporation of this solid waste into geotechnical projects can serve to mitigate the environmental impact of its disposal. The results of the characterization, static, and dynamic tests performed on a Brazilian lateritic clayey soil and soil-rubber mixtures are presented in this study. The tests were conducted with pure soil and with soil-rubber mixtures in proportions of 2.5%, 5.0%, 7.5%, 10.0%, 12.5%, and 15.0% of rubber weight in relation to the weight of the pure soil. A novel methodology for determining the damping ratio (D) parameter directly from the top of the compacted pure soil and soil-rubber mixtures is presented. Based on this study, the rubber from shredded scrap tires can be used in applications such as compacted embankments, soil walls reinforced with geosynthetics, and seismic barriers. However, it is not recommended for use in pavement layers. The results indicated that the increase in the percentage of rubber leads to the decrease in the following parameters of the mixture: resilient modulus, shear modulus, elastic modulus and damping ratio. The cohesion of the mixture increase slightly, as the percentage of rubber increase.

Abstract in English:

Abstract Extensive and accurate data from on-site testing is increasingly fundamental in determining design geotechnical parameters of offshore structures. As a novel method for assessing offshore soil, the T-bar penetrometer offers benefits such as high precision, reliability, ample data acquisition and cost-effectiveness, but its application in offshore projects remains limited. In this research, a set of approaches are used to analyze the evaluation of penetration rate effects in a kaolin and bentonite mixture prepared to reproduce Brazilian offshore soil conditions aiming the development of in situ testing technology in the marine engineering area. Miniature T-bar penetrometer tests (10 mm diameter and 50 mm length) at constant driving penetration rate were performed at 0.05; 0.1; 0.25; 0.5; 1.0; 2.5 and 5.0 mm/s. In addition, three variable rate tests (twitch tests) were performed aiming to analyze the penetration rate reductions at each twitch stage. The measured resistances and the drainage conditions were interpreted using the normalized velocity (V), and the results show a strength increase by viscous effects of 10% for each logarithmic cycle of penetration rate increase. The results suggest that the transition between the undrained and partially drained penetration occurs at normalized penetration rates between 20 and 50. These results agree with values previously published in the literature and unequivocally demonstrate how the influence of penetration rate can impact the measured undrained shear strength for T-bar tests. It is concluded that the influence of the test penetration rate on the measured resistance cannot be disregarded in intermediate permeability soils.

Abstract in English:

Abstract Understanding the effects of installation method on a deep foundation is fundamental for analyzing load test results and improving foundation design based on soil profile characteristics. This study analyzed 40 load-displacement curves of driven piles and piles bored using a manual auger, measured 20 cm in diameter and 3 or 6 m in length. Piles were constructed at the Experimental Field of Geotechnical Engineering, State University of Londrina. The soil is classified as silty clay, exhibits collapsible behavior up to a depth of 7 m, and has low resistance in surface layers, according to the results of particle size analysis and the standard penetration test. Load tests were carried out under static conditions using mixed loads. Natural moisture conditions were used in the test, and pre-wetted conditions in the retest. For three bored piles, these conditions were reversed. Pre-wetted conditions resulted in loss of failure load, highlighting the collapsible nature of the soil. Conversely, piles tested under natural moisture conditions exhibited higher failure load. Load-displacement curves showed shapes consistent with the expected for the analyzed pile types. This consistency supports the discussion on the effect of the construction method on pile behavior, demonstrating that soil removal during excavation for pile boring mobilizes side friction, whereas, in driven piles, soil compaction enhances toe resistance, particularly for piles constructed by concrete pounding as compared with concrete casting.

Abstract in English:

Abstract This paper presents analysis and discussion of an urban vertical excavation, with the soil nailing technique, in fine-grained soils with high plasticity. The excavation was numerically evaluated using finite element analysis (FEA) using a 3D finite element model (FEM). Several field and laboratory soil investigations were conducted, interpreted and used in the FEA. The FEM model was calibrated using instrumentation and monitoring results during the soil nailing construction. Analyses were conducted focusing in horizontal displacements, nail pullout strength, nail tensile load, soil stress state, and tensile load at the nail head. The results showed that the behavior of the soil nailing retaining wall in fine-grained soils differs significantly from what is typically reported in the literature for non-cohesive soils. The high apparent cohesion of the fine-grained soil resulted in good performance, with reduced horizontal displacements on the face and lower tensile loads in the nails and at their head.

Abstract in English:

Abstract The metropolitan region of Belo Horizonte city is home to several high-risk areas with a significant number of mass movement occurrences. Additionally, there are cases of movements in areas that are not considered high-risk, where constructions exhibit a medium to high construction standard. This emphasizes that, in addition to disordered occupations, the terrains have a natural susceptibility to the process. Intervention in slopes through cuts and fills is an unquestionable necessity in geotechnical projects to reinforce unstable or damaged areas. This article explores the field of soil nailing and presents the necessary design practices for its utilization, including safety checks based on deterministic, probabilistic, and finite element analysis. The case study is based in Belo Horizonte, more specifically in the ‘Buritis’ neighborhood, Brazil. The reinforced slope has a height of 18.5 meters and covers a total area of 1425 square meters. Based on different methodologies, the solution was validated as the most technically feasible, executable, and financially viable.

Abstract in English:

Abstract In a homogeneous earth fill dam, an initial process of internal erosion was observed near the base of the downstream slope, which is one of the main dam failure causes in the world. This problem was adequately solved, and research was started aiming to find the causes of the detected anomaly. The history of the structure was investigated, field testing results were analyzed and undisturbed samples were collected in different regions of the dam. Characterization tests, saturated permeability coefficients tests under different effective stresses and flow directions, and Filter Papel tests were run. Results were incorporated into computational models to investigate the behavior of hydraulic gradients and the height of the exit point of the phreatic line defined on the basis of monitored piezometers installed at the site. The software Plaxis LE was used in this study. It was evaluated whether the adoption of unsaturated parameters or 3D analysis would promote any change in the flow pattern in the studied structure, which did not occur. It was also considered whether the soil-atmosphere interaction could generate critical hydraulic gradients through rainfall and evaporation cycles, but there were no critical results either. Finally, it is concluded that effects of natural vegetation previously found in Dam X may have led to the observed internal erosion process. These somewhat unusual findings are relevant for improving the understanding of vegetation impacts on earth dam safety and can help guide future monitoring and, particularly, maintenance practices to prevent similar issues in other similar earth fill dams.