Leandro Alejano

University of Vigo | UVIGO · Department of Natural Resources and Environment Engineering

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-perme-ability rock known as Blanco Mera granite, we have pe...

This study aimed to explore and compare the application of current state-of-the-art machine learning techniques, including bagging (Bag) and rotation forest (RF), to assess landslide susceptibility with the base classifier best-first decision tree (BFT). The proposed two novel ensemble frameworks, BagBFT and RFBFT, and the base model BFT, were used...

The convergence-confinement method (CCM) is a simplified widely utilised tool for assessing the interplay between the rock mass behaviour and the support effect, so it is quite helpful for tunnel support design purposes. However, the direct application of this technique has shown some limitations, many of which are directly related to the three-dim...

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 con...

Toppling of individual rock blocks resting on an inclined surface has often been observed in nature. This instability mechanism has typically been analysed for simple block geometries, considering the contact between the block and the base where it lies is a planar surface. In this study, the authors analyse the case where this contact is a regular...

The main aim of this study is trying to contribute to a better understanding of the role of surface roughness basal planes on toppling-related instability phenomena. In this way, the authors focus on the stability against toppling of a single block resting on a regular rough surface. To do that they have first artificially created sample rock block...

Wildfires and rockfalls are among the major hazards in forested mountainous regions across Europe. Understanding processes and conditions that lead to rockfalls during and after a wildfire in different geological contexts is, therefore, of great relevance. The increase of rockfalls associated with the occurrence of wildfires is connected to several...

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...

Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confineme...

This study investigates the tensile failure mechanisms in granitic rock samples at different scales by means of different types of tests. To do that, we have selected a granitic rock type and obtained samples of different sizes with the diameter ranging from 30 mm to 84 mm. The samples have been subjected to direct tensile strength (DTS) tests, ind...

Roofing slate was traditionally quarried in Spain for roofing purposes since the Middle Ages. 40 years ago, and due to an increasing market demand from European countries, convenient prices and depletion of old quarries, producers envisaged the underground exploitation of these deposits. Nowadays, there are some underground room and pillar roofing...

RESUMEN Comprender las condiciones que producen los desprendimientos de rocas durante y después de un incendio forestal, es un gran reto al que se expone la comunidad científica, con el fin de precisar el riesgo por este tipo de eventos. El aumento de desprendimientos de rocas asociados con los incendios forestales está relacionado con varios facto...

Highlights A review of the book “Convergence-Confinement Method for Tunnel Design” is provided. The book is put in the context of tunnel design methodologies. The contents of every chapter are briefly summarized. A very positive assessment is eventually issued.

Los diseños geotécnicos se basan en hipótesis y aproximaciones no siempre fiables, por lo que las incertidumbres del comportamiento de estructuras geotécnicas suelen ser mayores que las que se dan en otras estructuras de ingeniería. Así, las observaciones in situ y, en particular, la medición de magnitudes físicas específicas son el mejor antídoto...

An accurate evaluation of the shear strength of discontinuities is frequently a key aspect for determining the safety of mining and civil engineering works and for solving instability issues at rock mass scale. This is usually done by using empirical shear strength criteria in which the basic friction angle (φ b ) is a relevant input parameter. Til...

In numerical modelling, selection of the constitutive model is a critical factor in predicting the actual response of a geomaterial. The use of oversimplified or inadequate models may not be sufficient to reproduce the actual geomaterial behaviour. That selection is especially relevant in the case of anisotropic rocks, and particularly for shales a...

Se presenta en este estudio una caracterización detallada de una pizarra prestando especial atención a su anisotropía en términos de deformabilidad y resistencia a partir de ensayos de resistencia a compresión simple y triaxial en laboratorio. La pizarra es una roca metamórfica que presenta una marcada foliación o esquistosidad. Para realizar el es...

Granite boulders are characteristic geomorphological structures formed in granitic terrains. Due to their formation process associated with typical spheroidal weathering phenomena, they tend to show more or less ellipsoidal shapes prone to instability, and they often lie on small contact surfaces. Analyzing the stability of these boulders is not a...

We present the devlopment of low cost hydraulic fracturing triaxial devics

Prediction of the shear strength of rock discontinuities is usually performed by resorting to empirical shear strength criteria that depend on different inputs, some of which can be estimated through laboratory tests. Even though these tests are usually developed with rock materials, concrete is often used to make joint replicas. A relevant paramet...

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...

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 deforma...

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 s...

Scale or size effects of the uniaxial strength response in rock samples have been studied in detail in the past, so a good number of studies on different rocks are available. However, analyses on triaxial strength scale effects in rocks are scarce and they seldom address failure criteria (i.e. Hoek-Brown) evolution with specimen size. This obvious...

Probably, the most relevant issue in stability analysis of rock slopes is the correct identification of the potentially occurring failure mechanism, which should be mechanically analyzed to assess stability, later on. Traditional rock slope stability approaches consider planar, wedge, rotational and toppling failure as potential instability mechani...

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 infrastr...

When carrying out uniaxial, standard triaxial, or true triaxial compressive tests on rock, the strain response of the specimens can be measured directly or indirectly. The most commonly used devices are strain gauges (local direct measurements) and displacement sensors (global indirect measurements). Strain gauges are glued to specimens and directl...

This study investigates the existence and scope of scale effects over several eomechanical and geophysical properties of intact rock: uniaxial compressive strength, tensile strength, static moduli, ultrasonic pulse velocities and dynamic moduli. The study is focused in two relevant rocks of the Forsmark site and includes several experimental survey...

Twelve fracture toughness (KC) tests of specimens in granite to granodiorite (rock type 101057), sampled from a ground surface rock block of the Forsmark future high-level radioactive waste disposal site, have been performed using the ISRM’s SCB suggested method and the results have been compared with the newly developed pCT test methodology. Detai...

Understanding processes and conditions that lead to rockfalls during and after a wildfire in different geological contexts is crucial since this phenomenon is one of the major hazards in mountainous regions across Europe. Spain is one of the European countries with the highest rate of wildfires, and rockfalls cause high economic and social impact,...

The residual strength of rocks and rock masses is an important parameter to be constrained for analysis and design purposes in many rock engineering applications. A residual strength envelope in principal stress space is typically developed using residual strength data obtained from compression tests on many different specimens of the same rock typ...

In this paper we present a physical modelling approach where the stability of rock blocks against toppling in the field can be estimated using a tilt table, engineered rock models and 3D-printed small-scale versions of a natural rock boulder. To achieve this goal, first, simple geometry rock elements are tilted and results interpreted according to...

The preparation of standardized samples of soft rocks for the development of uniaxial compressive strength (UCS) test is usually difficult, expensive and time-consuming. Needle penetration test (NPT) was originally developed in Japan as an alternative for the indirect estimation of uniaxial compressive strength of soft rocks. The needle penetromete...

Modelling of rock masses is important to assess the geomechanical behaviour of oil & gas reservoirs, especially in fractured tight reservoirs. The presence of discontinuities will significantly influence the general behaviour of the rock masses. In order to achieve realistic simulation process a good knowledge of rock behaviour is required together...

The presence of logan stones or pedestaled boulders is common in granitic environments. There are hundreds of examples of logan stones, many of them being next to inhabited areas, roads, main trails in natural parks and other zones where the fall of these structures could cause major damage. On the other hand, some of these boulders represent a tou...

The main aim of this study is the setting up of a laboratory system capable of testing fissured rock specimen permeability at different stress levels. To achieve this objective, a hydraulic press frame with associated Hoek's cell has been upgraded with servo-controlled pumping, pressure meter and external liquid weighing scales. Accordingly, and on...

Saw-cut rock surfaces, classically utilized to estimate basic friction angle of discontinuities by means of tilt test and other procedures, may seem planar to the naked eye. Nevertheless, they actually present roughness at a micrometric scale. Aiming at characterizing some of these saw-cut rock surfaces and assessing the possible implications betwe...

This study presents a calibration process of three-dimensional particle flow code (PFC3D) simulation of intact and fissured granite samples. First, laboratory stress-strain response from triaxial testing of intact and fissured granite samples is recalled. Then, PFC3D is introduced, with focus on the bonded particle models (BPM). After that, we pres...

Granite boulders are characteristic geomorphological structures formed in granitic terrains. Due to their formation process, they tend to show more or less ellipsoidal shapes prone to instability and they often lie on small contact surfaces. Analyzing the stability of these boulders is not a straight-forward task. First these boulders may topple or...

Various devices can directly or indirectly measure strain and record the deformational response of rock materials in uniaxial compressive strength tests. Strain gauges glued to specimens directly measure electrical resistance, while displacement sensors, typically linear variable differential transformers (LVDTs), indirectly measure linear displace...

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-des...

Control and monitoring of laboratory tests in the field of rock mechanics are usually expensive due to a wide variety of applications, normally carried out with very specific equipment (UCS and triaxial testing, tilt-test, permeability...). This fact may represent an issue for laboratories located in developing countries, but also for companies or...

This paper presents a case study of the stability analysis of over-tilted benches in an or-namental granite quarry. In order to facilitate quarrying of granite for ornamental purpos-es, the face of the benches of the exploitation are oriented parallel to the strike of the rift plane and to the so-called grain plane. The rift and grain are weakness...

The International Society for Rock Mechanics and Rock Engineering (ISRM) recommends to use the ISRM Suggested Methods (SM) to avoid problems during tests. In any case, fulfilling SM requirements does not ensure a proper result each time they are applied due to the natural variability of the rocks. Between others, there are some requirements regardi...

En este capítulo se muestran las técnicas y sensores que permiten realizar vigilancia y monitoreo de taludes.

In the European Union since 2010, the design of any type of structures must comply with EN-1997 Geotechnical Design (CEN 2004) (EC7) referring to engineering projects in the rock mechanics field. However, the design of debris flow countermeasures in compliance with EC7 requirements is not feasible: EC7 uses partial safety factors for design calcula...

The laboratory equipment is commonly expensive, making its acquisition difficult for laboratories and universities with low budgets. This problem could be solved with the use of open source software and hardware. Last decade, different initiatives were born that promulgate the use of these technologies for the design and construction of low-cost de...

In this work is presented an empirical-analytical method for the design of rock pillars in the underground mining of gold veins in Colombia. The proposal is focused in the observation of the failure mechanisms of existing pillars from real mines, field surveys, experimental rock mechanics and static analysis. The definition of the size of the pilla...

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 d...

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 first commercial underground rock caverns for hydrocarbon storage in South East Asia, the Jurong Rock Caverns Project (JRC Project), have recently been completed in Singapore. The storage capacity of 5 caverns is 1.47 million cubic meters and 3.5 million cubic meters of rocks were excavated in this project. Geologically, it was excavated in low...

En este capítulo se describen las técnicas disponibles para proteger al macizo rocoso de las voladuras de producción.

One of the main inputs when estimating the shear strength of rock discontinuities, according to most existing strength criteria, is what is known as the basic friction angle, which is a parameter that responds to the frictional resistance of a planar, unfilled, and nonweathered rock joint. The basic friction angle can be estimated according to vari...

En este capítulo se describen los métodos existentes para estabilizar taludes

En este capítulo se describen los métodos existentes de drenaje de taludes

This paper summarizes a study carried out at the University of Vigo on the mechanical behavior of cylindrical specimens of eight different rocks, focusing on both pre-and post-peak behavior. First, more than 200 intact standard NX-sized specimens were tested under unconfined and confined conditions. Complete stress-strain curves were obtained for e...

En este capítulo se presentan las técnicas disponibles para evaluar el riesgo de accidentes por desprendimientos o caídas de rocas, entre ellas una desarrollada en la Universidad de Vigo específicamente para canteras. También se presenta una metodología sencilla de control de desprendimientos basada en la geometría de los taludes.

En este capítulo se dan las bases de los métodos estadísticos más usados en mecánica de rocas. También se da a conocer el carácter epistémico de algunos de los parámetros usados en mecánica de rocas, lo que dificulta la aplicabilidad del Eurocódigo-7 a la mecánica de rocas.

En este capítulo se trata sobre la aplicación de métodos numéricos en mecánica de rocas. Se da a conocer las bases en las que se fundamentan los distintos métodos y se dan reglas generales para la consecución de modelos numéricos exitosos

A database of post-peak triaxial test results was created for artificially jointed planes introduced in cylindrical compression samples of a Blanco Mera granite. Aside from examining the artificial jointing effect on major rock and rock mass parameters such as stiffness, peak strength and residual strength, other strength parameters related to brit...

Tilt tests have been used in situ and in laboratory as a practical technique to estimate the basic frictional component of rock discontinuities. A number of studies on tilt test results carried out by several authors revealed an unexpected variability of the results. To clear this issue, a statistical approach intended to allow a better understandi...

A key issue in rock slope stability analysis is the identification of the potential failure mechanisms, which are then mechanically analyzed. Traditional rock slope stability approaches typically contemplate planar, wedge, circular or rotational and toppling failure as potential instability mechanisms. For the case of toppling; block, flexural and...

Una vez conocidas las potenciales roturas que se pueden producir en taludes, es necesario conocer las técnicas disponibles para analizar esas potenciales roturas. Comenzamos en este tema con la más sencilla, la rotura plana, que si bien no es muy común, sí es fácil de comprender y permite introducir conceptos que se utilizarán en otros tipos de ro...

Una vez conocidos los fundamentos del comportamiento mecánico de las rocas, las discontinuidades y los macizos rocosos, llega el momento de aplicarlo al análisis de la estabilidad en taludes en roca. El primer paso en ese análisis es la identificación de los posibles mecanismos de rotura que se pueden producir en taludes, por ello en este tema se p...

Continuamos mostrando las técnicas disponibles para analizar las roturas en taludes. En el caso de este tema se describe cómo analizar las roturas por vuelco y las roturas por discontinuidades paralelas al talud (roturas de talud de muro).

Finalmente, en este tema se muestran las técnicas disponibles para analizar las roturas circulares.