Resumo em Inglês:

Abstract Tabriz, as one of the most earthquake-prone cities in the Iran plateau, has experienced enormous earthquakes that have even destroyed the city altogether. Considering this seismological background and the vicinity of Tabriz's northwestern fault, reducing the possible earthquake losses can be highly useful by scrutinizing the strong ground motion resulting from the fault activation. To this end, a stochastic finite-fault ground motion simulation (EXSIM) method was applied as an important means for predicting the ground motion near the epicenter of the earthquake. EXSIM is an open-source stochastic finite-fault simulation algorithm that generates the time-series of the earthquake's ground motion. Based on the findings, the peak horizontal acceleration reached 0.83 g in the northern parts by creating artificial accelerograms and Tabriz's seismic zonation. In comparison, it reduced by 0.48 g by departing from the fault in the city's southern parts. Additionally, providing a seismic zonation map in Tabriz revealed that stopping the construction in the north parts while extending the settlement construction to the south part of the city are considered vital and unavoidable. Also, by applying the magnification and effects of the soil layers above the bedrock, it was further found that the existence of the loose layer with low strength and compaction intensify the application of seismic acceleration on the near-surface structures in the central, west, and southwest parts of the target area.

Resumo em Inglês:

Abstract Soil behavior is influenced by the void ratio and bonds between grains. The aim of this study was to describe the strength behavior of an aeolian sand from the dunes of Natal, Brazil, artificially cemented in unconfined compression tests. The influence of cement content and moisture on molding and the validity of using the void/cement factor in estimating unconfined compression strength (UCS) were assessed. Tests were conducted with samples using three molding moisture contents (6, 9 and 12%), four cement contents (2.5, 5.0, 7.5 and 10%) and a void ratio of 0.6 (Dr = 95%). The results showed that unconfined compression strength rises with increase in cement content and decreasing in molding moisture. The void/cement factor proved to be a reliable parameter in predicting the behavior of sand from Natal for the dosage of soil cement.

Resumo em Inglês:

Abstract This research work examines the utilization of cement in order to improve low plasticity clay soil. The soil samples treated with 2, 4 and 6% cement percents and cured for different curing times extended to 90 days. Laboratory investigations include unconfined compression, indirect tensile, gas permeability and microstructural tests, which were conducted on the tested samples. The soil-water retention behavior has been also investigated. The test results showed that the cement addition improved both the compressive and tensile strength properties of soil specimens. These strength properties were also increased with curing times. pH and electrical conductivity values were good indicators for the enhancement in the strengths properties. The results of micro structural tests illustrated that the natural soil specimens contain voids and the open structure. Further, these tests showed the cementation of soil grains and filling the voids among soil grains with cementing compounds. Gas permeability and soil-water retention behavior of soil specimens are strongly related to the variations in the soil structures. Further examination illustrated that in the case of low cement content, the pore size distribution (PSD) and the efficiency of gas permeability are more sensitive to curing times.

Resumo em Inglês:

Abstract In this paper a 3D numerical model using a software based on the Finite Element Method (FEM), was developed and validated using the results obtained in a geotechnical centrifuge model of a piled raft system founded in soft soils undergoing regional subsidence. The piled raft configuration had nine piles distributed in the center of the raft. The kaolin parameters were obtained, calibrated, and validated for the Hardening Soil Model (HSM), based on laboratory triaxial and oedometer test results. Also, a single pile load test was carried out in the centrifuge to get the resistance parameters used in the FEM. The developed numerical model reproduced satisfactorily soil and foundation consolidation displacements due, not only by the structural service load but also by the pore pressure drawdown. For load distribution on piles and raft, the model reproduces with good agreement the foundation behavior only for the structural service load, for pore pressure drawdown some adjustments on the embedded piles elements shaft and base resistance had to be done. The developed model allowed to identify the most sensitive parameters for this type of simulation, to define the types and stages of analysis that had the best fit for the physical model, and to obtain additional results to those measured in the physical model, e.g., the axial load distribution developed along the piles and therefore the magnitude of the negative skin friction, that is an important load that should be considered for the structural safety review of piled foundations subjected to this complex conditions.

Resumo em Inglês:

Abstract Laboratory compaction of soils is an important aspect in the selection of materials for earthwork construction. Owing to time constraints and concern for depleting resources, it becomes imperative that empirical relationships would be developed to predict compaction parameters, maximum dry unit weight (MDUW) and optimum moisture content (OMC) from easily measured index properties. The aim of this note is to develop empirical relationships between MDUW /OMC and logarithm of compaction energy (E)/fines content: sand content ratio (FC/SdC) for some lateritic soils. Index property tests were carried out on twenty (20) lateritic soils to classify them and obtain the FC/SdC. The soils were compacted at three compaction energies; British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). Two models were developed from relationships based on slopes and intercepts derived from MDUW/OMC versus log E plots; one model employs ‘FC/SdC’ and one compactive effort (BSL) while the other model employs only ‘FC/SdC’. The models were validated for robustness with soils used in the development of the models and six (6) other soils not used to develop the models. For the prediction of BSH, the model employing FC/SdC and one compactive effort showed typical errors of ±0.63 kN/m3 and ±0.76% for MDUW and OMC respectively. The model employing only FC/SdC showed typical errors of ±0.4 kN/m3 and ±0.83% for MDUW and OMC respectively. The typical errors are within allowed variations for projects and standards for MDUW and OMC, thus the models are quite robust.

Resumo em Inglês:

Abstract Owing to the comeback of small-scale models, this paper presents results of an experimental study based on the effect of underground circular voids on strip footing placed on the edge of a cohesionless slope and subjected to eccentric loads. The bearing capacity-settlement relationship of footing on the slope and impact of diverse variables are expressed using dimensionless parameters such as the top vertical distance of the void from the base of footing, horizontal space linking the void-footing centre, and load eccentricity. The results verified that the stability of strip footing is influenced by the underground void, as well as the critical depth between the soil and top layer of the void. The critical horizontal distance between the void and the centre was also affected by the underground void. Furthermore, the results also verified that the influence of the void appeared insignificant when it was positioned at a depth or eccentricity equal to twice the width of footing.

Resumo em Inglês:

Abstract Mass movements are frequent natural phenomena and especially dangerous due to increased population and irregular settlements in mountainous areas. Carrying out studies using methods that allow the numerical evaluation of their behavior is essential to mitigate and prevent these events' possible impacts. The traditional Limit Equilibrium and Finite Element methods fail to reproduce the problem from the beginning of the movement until the end of its development, so it is necessary to use new formulations. In this work the Material Point Method was selected to evaluate these movements in the stages of failure mode formation and development of landslide through an analysis of the soil shear strength and deformability parameters of a slope using the elastoplastic model with Mohr-Coulomb failure criterion. Maintaining a geometry and assuming soil mass behaves like a fluid, a single strength parameter and a single deformability parameter are analyzed to understand their influence before and after the failure.

Resumo em Inglês:

Abstract The SWCC has played an important role in studying the physical-mechanical behavior and hydraulic property of unsaturated soils. Laboratory experiments of SWCC were performed on unsaturated loess based on filter paper method considering freeze-thaw cycle, coupling of freeze-thaw cycle and dry-wet action. The main results indicate that: (1) With the increase of freeze-thaw cycle or freeze-thaw and dry-wet coupling, the matric suction was logarithmically decreasing and the dry-wet path affected matric suction significantly. There were obvious hysteresis loops between the two SWCC curves of different dry-wet paths, which increased with the increase of water content. (2) The Gardner Model was more appropriate to describe the SWCC, and through measured SWCC from Gardner Model and Childs & Collis-George Model, the prediction model of unsaturated loess permeability coefficient was gained, which had an exponential relationship with matric suction and a power function relationship with volumetric water content, respectively. (3) The vertical distribution model of permeability coefficient under one-dimensional steady state flow was established. The vertical permeability coefficient gradually decreased from groundwater table to ground surface, it decreased first then increased and gradually stabilized with the increase of freeze-thaw cycle at the same depth of soil.

Resumo em Inglês:

Abstract Chaos Theory is a mathematical theory devoted to study dynamic systems presenting very peculiar characteristics – sensitivity to initial conditions, positive or close to zero Lyapunov exponents, statistics governed by gaussian or non-gaussian distributions, among others - which make them, in the long run, unpredictable in time and space. This article aims at applying Chaos Theory to rockfall phenomenon. More precisely, the fall of unstable rock blocks was simulated through the RocFall 6.0 program by four preliminary case studies, having different rock slope geometry, different heights of the fall and blocks with different size and shapes. Moreover, the trajectories and reaches of gneissic rock blocks in a section of a phacoidal augen gneiss slope located in Morro do Cantagalo, in the city of Rio de Janeiro, were also simulated from the perspective of Chaos Theory. More precisely, the results suggest that the statistics of the number of fallen blocks at each end point of the trajectories located downstream of the respective slopes can be described by distributions derived from Chaos Theory. In addition, weakly or strongly chaotic behavior seems to be very specially associated with the concavity or convexity of the slopes.

Resumo em Inglês:

Abstract The inadequate disposal of hazardous solid waste has become a potential issue, mainly because of the impacts on the environment and human health. This occurs mainly through the contamination of subsurface soil and groundwater by leachates, which are often of the acidic constitution. To prevent such situations, the study of more efficient waste containment techniques has become opportune. In this way, this work was aimed to investigate the mechanical and hydraulic behavior of compacted clayey soil, with and without the addition of Portland cement (0 and 2%), submitted to the action of a sulfuric acid solution (2% volume concentration) and to a constant static vertical load (280 kN/m2), aiming at its prospective application as containment barrier. The experimental program comprised a few tests performed in an instrumented rigid-wall permeameter, during which the variations in hydraulic conductivity, shear modulus, and settlements were measured. The results showed that the hydraulic conductivity increased with cement addition when only water was percolated. During the acidic percolation, however, a reduction was observed only for the cemented soil. The acidic attack caused, almost instantaneously, an increase in the settlement rate and a reduction in stiffness, although a trend of stabilization was observed afterward.

Resumo em Inglês:

Abstract The behavior of tunnels in anisotropic rock masses is highly complex and heavily dependent on the orientation of the tunnel axis with respect to the geostatic principal stress directions and to the rock structural planes. 2D solutions cannot capture the 3D face effects of such complex scenario; thus, 3D numerical modeling is required. The modeling of such tunnels using conventional boundary conditions may be cumbersome since the tunnel may not be parallel to the boundaries. The issue is further complicated if the principal far-field stresses are not parallel to the principal axes of material anisotropy. In this case, the use of conventional boundary conditions may be problematic. In this paper, a new approach is presented to impose the boundary conditions and the far-field stresses on 3D numerical models of tunnels under complex ground and loading conditions. With the proposed approach, it is possible to easily simulate any orientation of the tunnel with respect to the principal directions of stress and material anisotropy. The numerical results obtained with the proposed approach were validated with an analytical solution and with numerical results using traditional boundary conditions.

Resumo em Inglês:

Abstract In recent years several dam failures have been reported throughout the world, generating a social concern on mine tailings. Along these lines, it became essential to understand the mechanical behavior of these materials in order to refine current design technologies and prevent more tragedies. In this context, this research had two main goals: (i) to analyze bauxite tailings mechanical behavior through isotropically consolidated-undrained triaxial tests and consolidation tests; and (ii) to compare triaxial tests and numerical simulations results. Confining stresses of 75kPa, 150kPa, and 300kPa were applied in the triaxial tests. Numerical modelling was performed through ABAQUS software, in which three different failure criteria were analyzed, Mohr-Coulomb Model (MCM), Drucker-Prager Model (DPM), and Modified Cam-Clay Model (MCCM). Results indicated that all studied criteria showed satisfactory results, however, DPM was the best criterion to simulate bauxite tailings mechanical behavior and respective strength parameters.

Resumo em Inglês:

Abstract In this paper, the progressive failure in an earth dam is evaluated upon a Multi-Laminate framework by considering 10 historical earthquakes in the world, along with their equivalent harmonic cyclic loading. Whenever the framework is given for any suggested plane by direction cosines, it has its certain direction, so, on this basis, the activation order of planes represents the direction and next step of progressive failure. The numerical integration comprises a function that is determined by distributing in sphere area including a radius of one, which can be approximated with several planes, tangential to different points in the sphere area. By calculating numerical integration, the quantity, spread on the sphere, achieved in the aforesaid points to predict fabric anisotropy effects. The framework efficiency is proved by evaluation of removal constants, such as confining pressure, and void ratio. The effects of driven anisotropy studied on all planes of the framework in 10 earthquakes to determine the effects of induced anisotropy on activated and no activated planes, in order to evaluate the progressive failure. Then, the model is capable to predict the coordinate of node of each brick element of the earth dam for next failure.

Resumo em Inglês:

Abstract This note presents an alternative method for static load tests on piles (and caissons). Called Equilibrium Method by its first proponents, the method was applied in some load tests in Brazil, in addition to being the object of theoretical studies conducted at the Federal University of Rio de Janeiro. The method consists, in each step, to keep the load constant for a period of time and then let it relax (not pumping the jack) until the displacement and the load reach mutual equilibrium. The stabilized displacement and the relaxed load (the so-called load and displacement in equilibrium) are considered for the load-displacement curve. The method has the advantage of producing the load-displacement curve close to that of a slow, stabilized test (incremental slow maintained load test), but with a shorter total execution time. The paper includes a short theoretical background and a review of the Brazilian experience.

Resumo em Inglês:

Abstract Erosion processes occur in several locations, causing impacts on the environment. This article analyzes the soil erodibility potential of the conservation unit of Timbaúbas municipal natural reserve, located in Juazeiro do Norte, in the southern mesoregion of Ceará, northeastern Brazil. It also addresses geotechnical characterization tests and field tests on erosion. In the field tests on erosion, huge volumes of soil loss were found caused by the action of rainfall and simulated surface flows. The results of the geotechical investigaton revealed silty sand soil, low values resistance parameters, has high erosion potential. The reduced rate of soil vegetation cover associated with the mechanical characteristics of the aggregate increases susceptibility to erosion processes, also intensified by anthropic intervention and construction of buildings on the site, without proper action to discipline the runoff. This work enables us to conclude that natural factors together with unsuifigure anthropic factors have been the causes of erosion of the conservation unit in question.