Issue 189 by Leandro R. Alejano
We statistically analysed the chemical components present in waste water from mines in Galicia (N... more We statistically analysed the chemical components present in waste water from mines in Galicia (NW Spain). These elements pose a risk
to public health and the environment, most particularly in the event of a failure in the containment structure of a pond or dam.
The statistical processing of the data, which started with an analysis of the typical contaminants present in mining ponds and dams,
pointed to the potential limitations of using non-spatial models for spatially structured data.
Our results indicate the greater potential of the generalized linear spatial model over the generalized linear model for analysis of spatially
structured data. We also show how a misspecification of the model for analysing spatial data can lead to misleading conclusions, which
might lead, in turn, to poorly designed protective or corrective measures.
Papers by Leandro R. Alejano
IOP conference series, 2023
There are not many studies on jointed rock specimens, which can be considered small scale rock ma... more There are not many studies on jointed rock specimens, which can be considered small scale rock mass analogs. On the other hand, the scale effects in the mechanical properties of such samples have seldom been studied. With the aim of continuing previous research on intact granite rocks, the authors have carried out sets of 25 stress-strain triaxial compressive tests on 1 sub-vertical and 2 sub-horizontal 38 mm, 54 mm and 84 mm diameter jointed granite specimens at various confinements. Peak and residual strength values were obtained and compared to those recovered form intact rock samples. Results suggest that peak strength follows similar trends with scale to those observed on intact rock, even if lower strength values are logically recorded. Regarding residual strength, the obtained results are in line with those observed trends for standard size samples, showing a similar trend for all cases independently of scale, even if we observe larger variability for jointed samples. The authors have also compared the values fitting the generalized Hoek-Brown criterion for rock masses to better understand the behavior in relation to sample size. So scale effects clearly appear on jointed rock peak strength of jointed sample; even if residual strength seems hardly affected by scale.
Rock Mechanics and Rock Engineering
Understanding size effects is important to rigorously analyse the behaviour of rocks and rock mas... more Understanding size effects is important to rigorously analyse the behaviour of rocks and rock masses at different scales and for different applications. A number of empirical and numerical studies have included size effects on the uniaxial compressive strength of different rocks, but only few have focussed on the triaxial compressive strength. In this study, several triaxial tests were conducted on granite samples at different confinements (from 0.2 to 15 MPa) and sizes (from 30 to 84 mm in diameter). The most relevant strength parameters were recovered including peak and residual strengths, orientation and frictional response of shear bands. Size effects were observed to be less dominant at high confining pressures for both peak and residual strengths. The resulting data were analysed in the context of size-dependent rock strength theories. For peak strength analyses, the unified size effect law (USEL) and the improved unified size law (IUSEL) were used, in which the double trends,...
Geomechanics and Geophysics for Geo-Energy and Geo-Resources
We have designed and built a versatile testing device to perform hydraulic fracturing experiments... more We have designed and built a versatile testing device to perform hydraulic fracturing experiments under true triaxial conditions. The device, based on a stiff biaxial frame that can be installed in a servocontrolled press, can accommodate cube rock samples of up to 150 mm-edge. Using a low-permeability rock known as Blanco Mera granite, we have performed a series of tests across a range of confining pressures including hydrostatic, normal, and strike-slip regimes. We have verified the applicability of two simple fracture mechanics-based models for the interpretation of experimental results, and we have determined the value of tensile strength of the rock from the injection curves recorded. The orientation of the hydraulically-triggered fractures with respect to the applied stress has also been analyzed. Although the models proposed by Rummel and Abou-Sayed provided reasonably satisfactory results, especially for hydrostatic and strike-slip tests, the presence of heterogeneities and ...
Journal of Rock Mechanics and Geotechnical Engineering
Rock Mechanics and Rock Engineering
Large granitic boulders resting on steep slopes represent considerable safety hazards that largel... more Large granitic boulders resting on steep slopes represent considerable safety hazards that largely depend on the location of the contact surface characterized by the impression d, denoting the parallel distance between the contact surface and the original rock surface. On the other hand, this impression reflecting the often convex nature of the contact between boulders and resting platforms, cannot be measured precisely, so Factors of Safety (FoS) computed with this input may have significant uncertainties. Using geometric 3D analysis, here, we present the concept of computing FoS as a function of the impression d, admitting a much more reliable estimate of the actual hazards. Beyond introducing the FoS functions, we also identify all failure modes, some of which have not yet been investigated. We compute the FoS functions for the boulder Pena do Equilibrio, located in Spain. Our computations for FoS against sliding match all earlier results. However, we also compute FoS against top...
espanolEl angulo de friccion basico (ɸb) es un parametro esencial para la estimacion de la resist... more espanolEl angulo de friccion basico (ɸb) es un parametro esencial para la estimacion de la resistencia al corte de juntas de roca, de acuerdo a la ecuacion de Barton y a otros criterios sugeridos. Este parametro se puede obtener en laboratorio mediante el ensayo de inclinacion o tilt test. Sin embargo, aun no existe una metodologia sugerida o procedimiento generalizado para la obtencion de este parametro de manera experimental. En el presente estudio se investiga el efecto del desgaste, consecuencia de las sucesivas repeticiones del ensayo sobre la misma superficie de roca, asi como la posible influencia de la velocidad de rotacion de la mesa de inclinacion sobre los resultados. Se han estudiado cinco velocidades distintas, con cinco juntas para cada velocidad y cinco ensayos para cada junta, para el caso de un granito medianamente meteorizado. Los resultados indican que, si bien la velocidad de rotacion no afecta de manera significativa a los resultados, el efecto del desgaste jueg...
International Journal of Rock Mechanics and Mining Sciences, 2021
Slates are metamorphic rocks characterized by the pervasive occurrence of cleavage or foliation p... more Slates are metamorphic rocks characterized by the pervasive occurrence of cleavage or foliation producing a highly anisotropic mechanical behavior characterized by fissility. Deformability and strength of these rocks are therefore dependent on the cleavage plane orientations relative to the principal stresses. In this study, the failure and deformability of these rocks are experimentally investigated by means of a set of standard uniaxial and triaxial compression tests on samples cut with the cleavage forming different angles. Propagation velocity measurements have also been taken in a good number of specimens. Compression tests show that deformability and strength are clearly anisotropic for this rock and that failure through the cleavage plane is observed in the range of dip angles from 15 to 75 •. Transversely isotropic elastic parameters are fit based on improved existing approaches. Moreover, the strength of tested samples cut normal and parallel to foliation relevantly differ, something noted qualitatively in the past by some authors in some metamorphic anisotropic rocks. However, this difference has neither been explicitly reported for the case of other foliated sedimentary rocks such as shales, nor formalized in theoretical strength approaches. The triaxial compression experimental data on slates were fit with the Jaeger's plane of weakness (JPW) model. Strength criteria differentiating the strength in directions normal and parallel to foliation are proposed to adapt the JPW model to the observations in slate strength behavior. Other model improvement is proposed, the use of a non-linear strength criterion for the intact rock (Hoek-Brown), which shows to better represent observed strength laboratory results.
Tunnelling and Underground Space Technology, 2021
When carrying out compressive tests on rock specimens, a stress plateau is typically attained fol... more When carrying out compressive tests on rock specimens, a stress plateau is typically attained following peak strength within a strain range a few times larger than the strain at peak strength. This stress level is commonly known as residual strength. A large database of these tests on granitic rock specimens has been compiled and analyzed in detail with the aim of improving understanding of the residual strength of this type of rock. It is observed that physical scale does not significantly change this residual strength. This stress threshold is also shown to be independent of the initial level of jointing in the rock volume. The implication of these findings is that residual strength derived from rock specimen testing can be potentially extended to rock mass scale, at least for granitic rocks. Three one-parameter residual strength models have been used to fit laboratory test residual strength data of granitic rocks, and all of them are shown to reasonably approximate the actual data. Additionally, the residual laboratory strength parameters of all the varied studied granitic rocks for varying scale and pre-jointing tend not to be very different, covering a limited range of values. Ultimately, the potential errors in simple excavation analysis that might result from a priori assumptions regarding the residual strength of granitic rock masses are quantified.
IOP Conference Series: Earth and Environmental Science, 2021
Debris flows are dangerous natural processes that cause extensive damages to infrastructures and ... more Debris flows are dangerous natural processes that cause extensive damages to infrastructures and urbanized areas and can lead to loss of human lives. Their unpredictability, their extremely high motion and their magnitude are the main causes of these harms. Mitigation measures are fundamental for reducing the associated risk and protecting infrastructures in mountainous areas. Their design is still an open issue: there are many formulations to evaluating impact pressure. Moreover, the uncertainties in the determination of flow characteristics (velocity and thickness) are significantly high and difficult to quantify. In the European Union, the design of any type of structures involved in rock mechanics field must comply with EN-1997 Geotechnical Design (CEN 2004) (EC7). For debris flow countermeasures, EC7 requirements are very difficult to apply in practice since partial safety factors are not provided for these phenomena. However, the basic philosophy of reliability-based design (R...
IOP Conference Series: Earth and Environmental Science, 2021
The basic friction angle of rock joints is usually obtained from tilt tests, being the most commo... more The basic friction angle of rock joints is usually obtained from tilt tests, being the most common the laboratory tilt tests. This test has been standardized according to the ISRM. However, most of the times when calculating the shear strength of discontinuities, reference tables are used to obtain the basic friction value for the lithology under study. These tables omit some lithologies complicating the search of adequate references. An alternative, straightforward and economical way to obtain ɸb is through the field tilt test, which is carried out by sliding two blocks aside a joint. It is a well-known test, but there are few references to its implementation. In this test, unlike the laboratory tilt test, the samples are not "polished" and it is necessary to evaluate the roughness of the joint and the normal component to the weight of the upper blocks. The idea is to calculate the term of ɸb from the Barton-Bandis' equation and include the tilt angle α. Various tilt-test measurements were carried out with field blocks on both sides of the same joint, considering different lithologies (granite, limestone, andesite, dacite, coal and slate) and block sizes, evaluating the ideal ranges of applicability of the test.
Rock Mechanics and Rock Engineering, 2020
The preparation of standardized soft rock specimens to perform unconfined compressive strength (U... more The preparation of standardized soft rock specimens to perform unconfined compressive strength (UCS) tests is typically difficult, expensive and time-consuming. Needle Penetration Test (NPT) was originally developed in Japan as an alternative for the indirect estimation of UCS of soft rocks. The needle penetrometer is a simple, portable and non-destructive testing device that measures applied load and penetration depth for the rock to calculate the needle penetration index (NPI). A complimentary, portable and widely used destructive test is the point load test (PLT), which measures regular and irregular specimens by the application of a concentrated load using two coaxial conical platens that yield the point load strength index (IS(50)). We investigated and compared the NPT and PLT in terms of measuring changes induced by water saturation and obtaining UCS and the static Young's modulus (Est) for dry and saturated soft sedimentary rocks. The results point to significant correlation functions from which to infer UCS and Est in terms of NPI and IS(50) in dry and saturated soft rocks. Furthermore, both NPT and PLT are suitable tests for evaluating changes in strength and deformability induced by water saturation. We also found a good correlation between the NPI and Is(50) .
Landslides, 2019
After a recent forest fire, a weathered granite rock slope located in the northwest of Spain may ... more After a recent forest fire, a weathered granite rock slope located in the northwest of Spain may become increasingly susceptible to rockfalls. This study presents a multi-approach assessment of rockfall hazard, with some features deserving particular attention. First, the geomorphological context represented by a weathered rock mass with multiple dispersed blocks presenting various potential instability mechanisms. Secondly, the presence of a hillfort behind the slope and a small village at its toe, limiting the available solutions for rockfall protection. Finally, the combination of different remote sensing techniques (unmanned aircraft system topography and light detection and ranging) with a semiautomatic geostructural analysis has been successfully applied to obtain both a 3D point cloud of the wide area under study in addition to an estimation of mean block volume for rockfall simulations. Additionally, the design and implementation of a protective measure (rock dynamic barrier) have been addressed.
International Journal of Rock Mechanics and Mining Sciences, 2019
Granitic boulders are widespread geomorphological elements, particularly found in humid granitic ... more Granitic boulders are widespread geomorphological elements, particularly found in humid granitic areas. Although they seldom represent a hazard for people or infrastructures, sometimes their location in steep or natural slopes may jeopardise their stability and potentially affect people or infrastructures. In addition, their complex geometry makes the instability mechanisms difficult to identify, so it is even more difficult to compute factors of safety regarding their stability. In this paper, the authors analyse potential failure mechanisms of granite boulders based on analytical mechanic calculations and physical tilt tests, permitting understanding the phenomena under scrutiny. Then, they study the stability of one of these boulders: the Pena do Equilibrio or equilibrium rock. To do that they resort to standard geotechnical characterization and advanced geometrical characterization derived from UAV photogrammetric and 3D Laser Scanning of the boulder. The presented results exemplify how the application of these recently available topographic technologies, in combination with rock mechanics approaches, enable a rigorous analysis of the stability of granite boulders.
Procedia Engineering, 2017
The complete stress-strain response of a number of intact rocks-including igneous, metamorphic an... more The complete stress-strain response of a number of intact rocks-including igneous, metamorphic and sedimentary ones-has been studied based on more than 300 compressive uniaxial and triaxial strength tests. Obtained results have been typically interpreted to register peak and residual strength as well as other post-peak parameters. Particular attention was given to the study of dilatancy. Dilation angle of these intact rocks was fitted to two pioneering but still recent dilatancy models (Alejano & Alonso 2005; Zhao & Cai 2010), having the feature of being plastic-shear-strain and confinement-stress dependent. The aim of this paper is to identify various dilation trends according to the type of rock tested and to check the ability of the models to accommodate actual results. This can be the base to further extend these models to the rock mass scale. To do that, the dilation angle database produced in our laboratory and some results from other tests taken from literature have been compiled in order to explain the main behavioral trends of this parameter according to the addressed models. These approaches are intended to insight rock behavior models emphasizing the post-failure stage as well as to contribute to more realistic but still practical dilatancy models.
Journal of Rock Mechanics and Geotechnical Engineering, 2014
Rock Mechanics for Resources, Energy and Environment, 2013
In 2010, the Eurocode for Geotechnical Design, EN-1997-1:2004 (CEN, 2004), informally known as Eu... more In 2010, the Eurocode for Geotechnical Design, EN-1997-1:2004 (CEN, 2004), informally known as Eurocode 7 or EC7, became the Reference Design Code (RDC) for geotechnical design - including rock eng ...
DYNA, 2015
We statistically analysed the chemical components present in waste water from mines in Galicia (N... more We statistically analysed the chemical components present in waste water from mines in Galicia (NW Spain). These elements pose a risk to public health and the environment, most particularly in the event of a failure in the containment structure of a pond or dam. The statistical processing of the data, which started with an analysis of the typical contaminants present in mining ponds and dams, pointed to the potential limitations of using non-spatial models for spatially structured data. Our results indicate the greater potential of the generalized linear spatial model over the generalized linear model for analysis of spatially structured data. We also show how a misspecification of the model for analysing spatial data can lead to misleading conclusions, which might lead, in turn, to poorly designed protective or corrective measures.
Harmonising Rock Engineering and the Environment, 2011
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Issue 189 by Leandro R. Alejano
to public health and the environment, most particularly in the event of a failure in the containment structure of a pond or dam.
The statistical processing of the data, which started with an analysis of the typical contaminants present in mining ponds and dams,
pointed to the potential limitations of using non-spatial models for spatially structured data.
Our results indicate the greater potential of the generalized linear spatial model over the generalized linear model for analysis of spatially
structured data. We also show how a misspecification of the model for analysing spatial data can lead to misleading conclusions, which
might lead, in turn, to poorly designed protective or corrective measures.
Papers by Leandro R. Alejano
to public health and the environment, most particularly in the event of a failure in the containment structure of a pond or dam.
The statistical processing of the data, which started with an analysis of the typical contaminants present in mining ponds and dams,
pointed to the potential limitations of using non-spatial models for spatially structured data.
Our results indicate the greater potential of the generalized linear spatial model over the generalized linear model for analysis of spatially
structured data. We also show how a misspecification of the model for analysing spatial data can lead to misleading conclusions, which
might lead, in turn, to poorly designed protective or corrective measures.