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Abstract Surface roughness of coarse aggregates, regardless of its known influence in the bonding strength with the cement paste in the hardened state and in the viscosity of the composite in the fresh state, it still a barely researched... more
Abstract Surface roughness of coarse aggregates, regardless of its known influence in the bonding strength with the cement paste in the hardened state and in the viscosity of the composite in the fresh state, it still a barely researched and discussed topic. In addition, little is known about what rock characteristics influences the multiscale roughness of aggregates. This paper aims to evaluate the roughness of distinct types of aggregates in multiscale (macro and micro scale of roughness) using a 3D interferometer and establish a quantitative relation between the granulometry and mineral composition of the rocks and the surface roughness of aggregates. Six types of aggregates, five crushed and one gravel from riverbed, with sizes ranging from 19 to 25 mm were scanned. One sample from each type was chosen for a petrographic analysis. The six types of aggregates analyzed showed statistical differences between them in macro and micro scales of roughness. In the microscale roughness, basalt was considered the smoothest, and surprisingly, the quartzite (gravel), were one of the roughest. In the macro scale roughness, the quartzite (the gravel) was smoother than all the other samples due its rounded shape, while the gneiss was the most irregular particle and had the highest roughness. The quartzite (gravel) is a good example of how an aggregate could be very rough in a microscale (invisible to the naked eye), comparable to crushed aggregates, while being smooth to the touch and rounded. The weathering seems to affect the roughness at micro(nano)scales, independently of the roundness shape observed at millimetric scale. The micro scale roughness appeared to be related to the average size of the grains, the smaller the average grain size, the lower the micro scale roughness is. Rocks with aphanitic textures tends to fracture in smoother surfaces than rocks with phaneritic textures.
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The use of fiber optics as a tool for different kinds of geotechnical monitoring can become highly attractive and cost effective when compared to conventional instruments such as piezometers, inclinometers, among others. A single fiber... more
The use of fiber optics as a tool for different kinds of geotechnical monitoring can become highly attractive and cost effective when compared to conventional instruments such as piezometers, inclinometers, among others. A single fiber optic cable may cover a larger monitoring area compared to conventional instrumentation, and the possibility of monitoring more than one physical quantity with the same fiber optic cable. Consulting the literature, it is possible to find several different examples where distributed fiber optic systems are being used. For the use of any sensor, a calibration curve is required. In the case of strain sensors, calibration is required to derive strain values from the frequency measurement quantity. However, fiber optic sensor cable manufacturers often do not provide their own calibration parameters and consult the values in specialized literature, which can result in monitoring errors. In this context, this article presents a bench adjusted for tests on single mode fiber optic cables, as well as results of tensile tests aimed at defining the function of strain variations of two different optical fiber cables, manufactured by different companies, using two different distributed interrogators. This paper also proposes a methodology for calibrating of the fiber optic cables deformation since the calibration parameters are provided by the cable manufacturers, which can result in errors depending on the application. It should be noted that there are few manufacturers of fiber optic cables aimed at application in civil engineering. Therefore, with the calibration methodology proposed in this paper, it is intended to transmit to the academic community the possibility of obtaining calibration parameters of any fiber optic cable, even those manufactured for telecommunications purposes and not only for cables manufactured with the intended use in civil engineering. Because of this fact, researchers will not be restricted to the acquisition of special cables for their applications. Based on the results, it was possible to conclude that the application of calibrated fiber optic sensors in experimental piles foundations is viable, in order to evaluate the load-displacement behavior of these elements, under different loading conditions.
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When soils are inundated with liquids other than water, a physicochemical interaction takes place and can alter the soil behavior. Depending on the type of soil and on the solution, the soil can become more compressible and lose strength... more
When soils are inundated with liquids other than water, a physicochemical interaction takes place and can alter the soil behavior. Depending on the type of soil and on the solution, the soil can become more compressible and lose strength (or the contrary). In this paper, tropical residual gneiss soils are used, namely lateritic and saprolitic soils. The solution used are a mixture of sodium hexametaphosphate and sodium carbonate. Solutions were prepared with different concentrations such that the pH value remained at 10.5. Sodium concentration was used to interpret the results. Oedometer and triaxial compression tests were carried out with samples permeated with these solutions. The lateritic soil behavior was found to be quite distinct from the saprolitic one. While the lateritic soil becomes much more compressible upon the increase in the concentration of sodium, the saprolitic soil swells progressively. However, the compression curve converges at more elevated stress levels. The stress-strain curve also alters in relation to the concentration. The lateritic soil loses strength and its stiffness is greatly reduced with the increase in concentration.
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This paper shows how accurately and efficiently reliability analyses of geotechnical installations can be performed by directly coupling geotechnical software with a reliability solver. An earth slope is used as the study object. The... more
This paper shows how accurately and efficiently reliability analyses of geotechnical installations can be performed by directly coupling geotechnical software with a reliability solver. An earth slope is used as the study object. The limit equilibrium method of Morgenstern-Price is used to calculate factors of safety and find the critical slip surface. The deterministic software package Slope/w is coupled with the StRAnD reliability software. Reliability indexes of critical probabilistic surfaces are evaluated by the first-order reliability methods (FORM). By means of sensitivity analysis, the effective cohesion (\( c^{\prime} \)) is found to be the most relevant uncertain geotechnical parameter for slope equilibrium. The slope was tested using different geometries. Finally, a critical slip surface, identified in terms of minimum factor of safety, is shown here not to be the critical surface in terms of reliability index.
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Abstract The pull-off test (POT) is a tensile strength testing method that is widely used in concrete/mortar and was recently applied to rock mechanics. The POT can be easily performed in both the ...
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Abstract Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement... more
Abstract Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement conditions. Extreme concrete surface textures, including smooth, rough and rough–wavy textures, were reproduced. Surface plowing was assessed via image analysis, laser scanning and extended multifocal micrographs. The experimental results showed that smooth concrete surfaces exhibited high values of interfacial–to–internal friction angle ratios, ranging 88–90%, due to the angular shape of sand particles. The rough concrete surfaces generated higher interface strength than smooth concrete surfaces; however, the interface strength was still inferior to the surrounding sand strength. Surface plowing, which identified a mixed shear plane at the sand–concrete interface, was developed as particles were detached from the surface, thus inhibiting the interface friction angle from reaching the sand friction angle. Higher sand–concrete interface strength was achieved as surface waviness increased, and interface friction angles greater than the surrounding sand friction angle were reached. Under a constant normal stiffness condition, significantly high interface strength is achieved due to the increase of the current normal stress, which was directly influenced by the initial normal stress, stiffness, surface roughness, mean sand diameter and relative density; surface waviness did not have a marked effect on the normal stress variation. Based on these results, multiple regressions were proposed to estimate the sand–concrete interface strength by the interfacial–to–internal friction angle ratio and the effect of the constant normal stiffness condition.
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Certain tunnels of Vitória-Mina Railway have presented rock fall problems which do not represent major risks, but can impair the railway operation. The TUNELCON Project, partnership between Vale SA and Escola Politécnica da Universidade... more
Certain tunnels of Vitória-Mina Railway have presented rock fall problems which do not represent major risks, but can impair the railway operation. The TUNELCON Project, partnership between Vale SA and Escola Politécnica da Universidade de São Paulo (EPUSP), seeks to study the geomechanical behavior of these tunnels trough laboratory tests, geological and geotechnical mapping and numerical analyses. Therefore, it is important to collect large amount of data regarding to the rock mass geological and geotechnical characteristics that will be useful in further analysis.In this article the results of the roughness characterization of different discontinuity sets showed high variability for the shear fractures and foliation while relief fractures presented more constant values. The roughness was characterized by profilometer (Barton profilometer) and by 3D terrestrial laser scanner (3DTLS) images and their results were compared. Several Discontinuities from drill cores samples and 3DTLS mapping were used for this investigation.
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The number of great magnitude tailings dam collapses has made society increasingly aware of the need to better understand the risk associated with tailings dams’ collapse. Also, the analysis and studies of prior disasters should define... more
The number of great magnitude tailings dam collapses has made society increasingly aware of the need to better understand the risk associated with tailings dams’ collapse. Also, the analysis and studies of prior disasters should define the risk profiles and lead to the adoption of more adequate and successful policies and measures to reduce hazards. For this, we evaluated the material post-failure behavior, the construction methods, the failure causes and the geographical distribution of tailings dams’ failures worldwide. The post-failure behavior was evaluated by the occurrence or absence of flow sliding recorded after the collapse. The historical risks were analyzed by the F–N curve. It was thus possible to better understand these structures' safety historically, as well as to analyze their relationship with the material’s behavior. The statistics indicate the correlation between flow behavior and the event consequences. A correlation was also observed deriving from upstream failures, certain materials, some causes of failure and flow sliding. The F–N charts analysis remarks that the unsafety of tailings dams is due to upstream dams since other construction methods present risks under acceptable ranges.
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abstract: Bridges and tunnels are large and complex structures that demand periodic inspections to assess their physical conditions. Although both have different designs and constructions from each other, a common problem they share is... more
abstract: Bridges and tunnels are large and complex structures that demand periodic inspections to assess their physical conditions. Although both have different designs and constructions from each other, a common problem they share is the drawbacks that their conventional inspections face. Moreover, conventional procedures not only are laborious, time-consuming, and costly, but also involve high and/or hard-to-reach places, often exposing the specialized inspectors to danger. To overcome these problems, the Unmanned Aerial Vehicle (UAV) is being explored to automate these inspections. Recently, the number of researches employing it within the civil infrastructure condition assessment has been growing in recent years, especially for the inspection of large and complex structures. Unlike the UAV-based bridge inspection that already has some review articles available in the literature, there are none yet for the tunnel inspection, to the best of authors' knowledge. Therefore, this...
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Onshore wind turbine foundations are subjected to large overturning moments. The wind action imposes cyclic and dynamic loading conditions which occur in extreme and service scenarios. Deep foundations, when used, transfer this large... more
Onshore wind turbine foundations are subjected to large overturning moments. The wind action imposes cyclic and dynamic loading conditions which occur in extreme and service scenarios. Deep foundations, when used, transfer this large overturning moment through a pile group which combines the axial and lateral resistance of all piles. The paper explored the key aspects of onshore wind turbine foundations in Brazil. The main reason to explore this subject is that several authors consider onshore wind turbine foundations a well-understood topic; however, limited data from actual situations have been published, especially in developing countries where wind energy projects have only recently started. Thus, a survey of Brazilian energy companies and foundation designers was conducted, and the first Brazilian database of wind turbine foundations was created. This database contains data from more than three thousand Brazilian wind turbine foundations. The key aspects, types and dimensions o...