Ebook: Integrating Innovations of Rock Mechanics

This proceedings volume contains papers of the 8th South American Congress on Rock Mechanics (SCRM) held in Buenos Aires (Argentina) from 15 to 18 November 2015. The VIII SCRM was a Regional Symposium for South America of the International Society for Rock Mechanics (ISRM). Previous congresses have been held in Colombia (1982, 2006), Brazil (1986, 1998), Venezuela (1990), Chile (1994) and Peru (2010). After having traveled much of the continent, it is the first time that this congress was held in Argentina.

On this occasion, Buenos Aires-2015 merged three important events for the geoprofessionals. In parallel, SAIG, the Argentinean Society of Geotechnical Engineering, organized the 15th Pan American Conference on Soil Mechanics and Geotechnical Engineering (XV PCSMGE), the 6th International Symposium on Characteristics of Deformation of Soils (IS-BA2015) and the XXII Argentinian Congress of Geotechnical Engineering (CAMSIG XXII). The motto of the Congress, Integrating innovations of rock mechanics and rock engineering into the geotechnical world, indicates cooperation links within the geotechnical community.

This synergy brought together international experts, researchers, academics, professionals and geo-engineering companies in a unique opportunity to exchange ideas and discuss current and future practices in the areas of soil mechanics, rock mechanics; and its applications in civil, energy, environmental, and mining engineering.

Our goal and commitment was to organize meetings that will strengthen the link between academics and practitioners from North and South America.

On behalf of the Organizing Committee, the editors express their appreciation for the contribution made by all the supporters, sponsors, ISRM National Groups, authors, and staff of secretariat, who have made this congress a success.

Ricardo J. Rocca

Roberto M. Flores

Alejo O. Sfriso

Buenos Aires, 15–18 November 2015

The disturbance factor (D) included in the Hoek-Brown criterion represents a strength reduction parameter associated to the damage induced in large open pit slopes as a result of the blasting process and also as a consequence of the stress relaxation and stress rotations induced by the excavations during the mining process. The spatial distribution of the D factor, as well as its value, remain unresolved issues in the current rock mechanics practice applied to slope stability analysis. While it is reasonable to expect that in the long term, numerical modeling based on lattice formulations or strain softening constitutive models will be able to address this issue properly, the current state-of-the-practice (using both limit equilibrium and numerical modeling approaches) will remain applicable for some time. Current methods would therefore benefit from more robust guidelines to define the extent of the disturbed zone, as well as the distribution of strength degradation of the rock masses within a mined slope. In this study, an empirically-based guideline is proposed for the distribution of disturbance with depth in a slope. Furthermore, a first step is made at providing a mechanical interpretation of the disturbance of large open pit slopes in medium to hard rocks due to loss of confinement and is aimed at defining the extent of disturbance using lattice modeling. As the final purpose of the study is identifying the real effect of the disturbance in the strength properties and its location with respect to the slope surface, some initial attempts are also made to measuring the strength of undisturbed and disturbed rock mass samples using a Synthetic Rock Mass approach.

The West Wall of the Chuquicamata open pit has been historically referenced as an example of block toppling behavior, particularly in the upper part of the slope, located specifically in the material known as Fortuna Granodiorite and containing structural systems of significant persistence which dip into the slope at a somewhat steep angle. This rock mass is, in turn, supported on a strip of weak material associated to a shear zone located to the west of the main regional feature that defines the orebody, named the West Fault. Through the years, this failure mechanism has led to metric displacements which have accumulated and which continue to play a relevant role in the geotechnical design of the open pit. The mechanism, however, has been properly managed by the Geotechnical Direction staff at the mine, allowing the development successive pushbacks. Of relevance to the study presented in this article is the observation that whenever the mining plan of the pit involves excavations at the toe of the west wall slope (particularly in the referred shear zone), a correlation is observed with the activation of the slope, in terms of increased deformation rates for the wall. The observed behavior suggests that the interpretation of the west wall stability by means of the traditional factor of safety analysis is likely inadequate, as the slopes would be considered marginally stable and mining could have not been developed over the centennial life that the mine has had so far. Instead, a time dependent deformational approach seems to be a more appropriate option for dealing with slopes showing toppling behavior. A viscoelastic constitutive model is normally used to assess phenomena such as creep. This study summarizes the results obtained from a UDEC model developed for calibrating the observed behavior of prisms installed in the West Wall with readings ranging between years 1995 through 2013.

A execução de empreendimentos mineiros subterrâneos é uma atividade de alto risco que precisa de estudos geológicos/geotécnicos em diversos graus de detalhe. Isto é necessário para diminuir o potencial de instabilidade do maciço rochoso durante a operação extrativa, no caso em específico pelo método de câmaras e pilares, visando obter uma estimativa dos vãos máximos (spam), cálculo de resistência dos elementos de suporte naturais (pilares) e previsão de elementos de fortificação adicionais (tirantes e outros).

Por meio de dados de geologia regional, furos de sondagem e das próprias escavações, o estudo de caso da Mina Pilar de Goiás da Brio Gold contempla a caraterização das propriedades reológicas das rochas foliadas (xisto carbonoso/xisto sericitico), a distribuição da deformação frágil e a definição de rasgos estruturais maiores como dobras, falhas regionais e padrões de fraturamento associados.

Realizou-se análises de equilíbrio limite modelando os potenciais eventos de formação de cunhas, focando na interação da foliação com os diferentes elementos estruturais identificados.

A interação das atuais escavações com as informações estruturais detalhadas no ambiente e o histórico de eventos de queda de rocha registrados, foram utilizados para gerar setores de interesse para o mapeamento geotécnico (RMR e Q), possibilitando um zoneamento das áreas com caraterísticas similares.

Finalmente, essas regiões predeterminadas são consideradas como zonas de potencial risco geotécnico, permitindo definir parâmetros de estabilidade, tais como: orientação das escavações, dimensões máximas das câmaras e dimensões mínimas dos pilares a serem planejadas nas futuras áreas de produção.

Aunque el entusiasmo por las clasificaciones empíricas de macizos rocosos ha decaído en el último tiempo, los sistemas Q, RMR, MRMR y GSI se mantienen plenamente vigentes, siendo especialmente útiles en las primeras etapas de los proyectos de ingeniería de rocas. En este artículo se destacan errores que con frecuencia se cometen en la descripción geotécnica de testigos de roca, específicamente los relacionados con el grado de fracturamiento y la condición de las discontinuidades estructurales. La estimación de la calidad geotécnica de macizos rocosos puede resultar de tal deficiencia, que no permita decidir la continuidad de un proyecto de ingeniería en particular.

In underground mine projects, the in situ stress knowledge is essential, since those need, directly or as an input, the stress orientation and magnitude for the underground excavations design, their support and reinforcement, numerical modeling construction, mine method and mine sequence selection, rockburts prediction and others. The in situ stress knowledge is generally based on in situ stress measurements, as the overcoring technique. Since it has a high cost, generally this kind of measurements is limited to some measurements.

Nevertheless, different information can be used to the stress comprehension known as indirect and indicative techniques, like discing and breakout. The analyses and comparison of the direct measurements with discing and breakout information provided to the Cuiaba Mine considerable data for its in situ stress model construction.

Structural instabilities in open pit walls need to be assessed carefully for both safety and economic issues. Unstable wedges and daylighting blocks may be identified through three-dimensional (3D) image analysis, and determined in a first approximation by a discrete fracture network generation plugged into a polyhedral (rock block) model. To complete this preliminary assessment, a methodology for predicting failure inside the rock matrix is proposed by coupling discrete fracture network (DFN) modelling with the discrete element method (DEM). An identified wedge collapse that occurred in a coal mine is used to set up and to validate the model. In this case, the failure surface is shown to be well predicted by the progressive failure mechanism that develops from the toe of the structure inside the intact rock matrix. The DFN-DEM modelling is shown to be a complementary tool to assess rock slope stability in presence of non-persistent discontinuities.

The Province of La Rioja has geological features that give it great potential in dimensional stones. Some of these deposits are currently stalled due to problems to get the market. In order to study the effect of geomechanical properties of rocks in their ornamental quality, three sites were selected: a) Imperial Riojano Red Granite, b) Black Alcázar Granite c) Sierra lilac or blue Mara of Sierra de los Quinteros Granite.

To characterize the physical and mechanical properties of these rocks, the following studies were conducted in laboratory: petrographic characterization, physical indexes (dry and saturated density and % absorption), abrasion tests, uniaxial compressive strength in cubic samples and flexural strength on three and four points.

The results obtained shown that the geomechanical properties of lilac and black granites have very good proper for ornamental uses. The test indicates that these rocks are in the range of good quality granites in terms of physical and mechanical properties. The imperial red granite shows a good correlation between the microfracturing and the values obtained from mechanical and physical tests that make a lower quality of this rock. The black granite has very good properties for ornamental purposes, but the levels of jointing at a deposit scale, seriously limit the possibility to produce sized blocks required by the industry. One option to use this stone could be the production of small blocks for tile production but currently there is no market for that in Argentina.

This research provides the first steps in studying of Rock Mass – Shotcrete Interface behavior in creep process like the adherence generated in the interaction of both, which is determined by applying the criterion of shear strength for rough joints of Barton using destructive techniques like direct shear tests in samples physically simulated in laboratory.

Through the simulation, which allows designing models of real systems to experiment and understand the system behavior under evaluation, it was come to recreate physically in laboratory the parameters obtained during the rock mass geomechanical mapping. Parameters like the compressive strength and roughness joints were physically simulated using a high strength concrete at an age of 120 days. For shotcrete, it was come to assemble in laboratory a machine that simulates the process through compressed air and gravity flow.

Rock Mass – Shotcrete Interface at low age was simulated physically in 20 test samples were subjected by direct shear tests, in groups according to the different low ages of shotcrete.

A partir de la información obtenida de la instrumentación colocada en una excavación a cielo abierto y aplicando el método de análisis inverso, se presenta en este artículo la metodología empleada en la determinación de los parámetros geomecánicos del macizo rocoso donde se desplantó dicha excavación. Tomando en cuenta los resultados de la instrumentación, el modelo geológico definido durante la construcción, los datos de laboratorio de la roca intacta y mediante el uso del método de elemento finito, fue factible reproducir el comportamiento deformacional de la masa rocosa, cuya respuesta permitió estimar los parámetros geotécnicos necesario para evaluar la estabilidad de la masa rocosa en una etapa posterior a su construcción.

En el marco del seguimiento de la obra de construcción de la RN 150-Tramo Ischigualasto-Río Bermejo-Sección II-A1, perteneciente al Corredor Bioceánico Porto Alegre-Coquimbo, provincia de San Juan, encargada por Vialidad Nacional a la Escuela de Ingeniería de Caminos de Montaña (EICAM), UNSJ, se presentó un problema bajo la fundación del estribo de margen izquierda del puente sobre el río León. El mismo se encuentra fundado sobre areniscas duras pero que presentan diaclasas verticales muy abiertas que apoyan sobre lutitas meteorizadas que suprayacen a areniscas sanas. A medida que se iba construyendo la estructura, y debido a las tareas de excavación y la exposición al medio ambiente, las diaclasas se abrían cada vez más comprometiendo la seguridad del conjunto estribo-talud. En este artículo se plantea una alternativa tendiente a la estabilización del talud por delante del estribo mediante un muro de hormigón armado anclado al macizo rocoso y fundado sobre las areniscas sanas. Se hace un análisis de estabilidad global con el uso de un programa elaborado por la EICAM que considera la resistencia al corte no lineal de macizos rocosos diaclasados y un dimensionamiento del muro de hormigón armado anclado al macizo rocoso. El análisis se hace considerando cargas estáticas y dinámicas teniendo en cuenta la alta sismicidad de la zona.

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.

The geological and geotechnical characteristics of the proposed site for General Mugica multipurpose dam (Mexico) strongly conditioned its basic and executive design. The presence of a paleo depressed relief wrought in volcanic rocks (andesites and volcanic breccias) covered by deposits of fluviovolcanic origin (lahars), from the quaternary age, on the right margin of the project, imposed restrictions in terms of the load capacity of the foundation, deformability and permeability. This condition on the right margin forced to modify the initial concept of a comprehensive RCC dam about 90 m height, for an RCC mixed dam on the left margin and river bed, and clay core rockfill on the right margin. The permeability problems of the lahar and the implications of groundwater flow (hydraulic gradients and uplift pressure) in downstream slope stability were resolved by a drainage gallery excavated in the lahars deposit downstream of the dam axis.

This paper presents an example of 3DEC modelling of a rock tunnel using geological mapping obtained from 3D images of terrestrial laser scanner and the discrete fracture network approach. Three main discontinuity sets were identified in an 8-m-long section of a tunnel constructed in gneiss. The amount of discontinuity data obtained by 3D Terrestrial laser scanner mapping allowed the application of several sophisticated discontinuity analysis (orientation, size and frequency), and probability density functions were defined. These functions were used as input to discrete fracture network modeling, leading to a more representative 3DEC block model. Thus, if the mechanical characterization of the rock mass is also properly made, this approach can be used for stability analysis in rock mechanics. Specifically, it could be very useful for analyzing sections of uncoated tunnels in which the rock mass is strongly fractured.

The geotechnical characterization of the rock mass for rock-embedded pile foundations describes the particularities and their conditioning factors, in this type of project ranging from prospecting to completion of the foundations. Depending on the investigations, the project may be designed and implemented using a better safer, more economical and faster technique. The investigation activities involved: a) site: determining the Rock Quality Designation (RQD)and recovery using test cores, and b) laboratory: determining the physical indices (dry and saturated specific mass, porosity and water absorption), and uniaxial compressive strength, and petrographic analysis. The characterization of the rock mass involved in building the foundations does not finish at the design phase but continues steadily as the project progresses, with the controlled accuracy to refine methods, re-dimension structures and adopt solutions for the overall project. Based on this, expedite rock drilling was also accompanied for the geotechnical characterization and control of the pile foundations, which was a good control tool for this type of foundation. It is also used for confirming the cap rock and verifying less resistant layers, before or during pile driving, simplifying the services, at a faster rate and lower cost. The analysis of the physical indices was compatible with the indices existing for this type of rock and the analyzed rock masses demonstrated good characteristics to support a foundation.

National Road 150 passes through the central region of Argentina and is part of a bi-oceanic corridor from Brazil to Chile. In Sierra de Valle Fertil it has traversed sedimentary rock formations where they have built five bridges and six tunnels. During construction, instabilities phenomena were seen in both tunnels and surface works. In tunnels different behaviors were observed on hard rock and soft rock. Slope instability processes include mass displacement and failures due to decompression generated by excavation. Some reported cases occured during the execution of the work, including various types of failures. In many sectors, rock masses showed a high degree of weathering. Analyses for the design and mitigation actions undertaken are described. Details emerged in the foundation of the bridges that make the section also arise.

The highway BR 163 near the city Nobres, Mato Grosso State in Brazil has slopes with falling arenite blocks (fig. 1). The solution to this problem was a metallic mesh with a patterned of anchors. The software MACRO 1, from Maccaferri, was used to design the system. A secured drapery system, consisting of rockfall netting and a systematic nailing scheme, is designed to stabilize surficial material on an exposed rock face. The design procedure can be very complicated because the geomechanical models are very complex or unrealistic, and obtaining accurate input data is rather problematic. This paper presents a simple design approach for secured drapery system, which combines the field experience of geologists and engineers on one hand, and the results of full scale drapery field tests on the other.

La Isla de Madeira es territorio insular de Portugal, situada en el Océano Atlántico sobre la costa africana, es una isla volcánica, con una longitud de unos 50 km y relieve muy escarpado. Actualmente dedicada esencialmente al turismo, la isla soporta una población de unas 250.000 personas. En los últimos 20 años el gobierno autónomo se preocupó por desarrollar la infraestructura de caminos y obras hidráulicas. Estas obras implicaron la construcción de un gran número de túneles. En este trabajo se presentan algunos casos históricos de túneles viales recientemente construidos, dentro del mencionado encuadramiento socio-ambiental, características de los terrenos, datos históricos y referencias a túneles pioneros. Son desarrollados, en particular en este trabajo, el proyecto del túnel urbano del nuevo Acceso al Puerto de Funchal. En la parte (II) se presentan los túneles de la circunvalación de Madalena do Mar y el túnel 1 de la Vía Rápida construida en la cota 500.

La Isla de Madeira es territorio insular de Portugal, situada en el Océano Atlántico sobre la costa africana, es una isla volcánica, con una longitud de unos 50 km y relieve fuertemente montañoso. La comunicación sobre túneles viales de la isla se ha dividido por cuestiones de espacio en dos partes. En la Parte I se presenta un encuadramiento que es válido para ambas partes. De los túneles construidos en los últimos 20 años, túneles modernos, se presentan en el presente trabajo los túneles de la circunvalación de Madalena do Mar y el túnel 1 de la Vía Rápida construida en la cota 500.

Slopes instabilities pose a significant risk to infrastructures and development especially in mines and mountainous areas. The management of geohazards in France takes place in a wide range of environments exposed not only to rockfall, but also avalanche, flooding, earthquake or volcanoes, from high mountains to tropical islands territories. Therefore a specific approach has been developed from decades of experience (since 1860) and now known to be one of the most conservative in Europe. Indeed risks are being increased in the French Alps by global climate change (Mediterranean storms) at the same time as the density of infrastructure, mines or industrial projects increase. Over recent years research and new developments are increasing knowledge of slope stability, leading to new engineering methods and mitigation options especially in the range of dynamic barriers conception or high energy passive bunds. Experience between private companies and public services have been applied. This diversity through centuries of experience and some major disasters, led to a balanced management strategy always bringing in pioneering measures such as recent European and French guidelines. Finally, operational feedback of some cases studies of roads and industrial sites protection are described as example. This shows mainly the importance of the analysis process through fine engineering studies and the combination of different protective strategies and lightweight preventive measures.

Drilling activity has radically increased in unconventional shale gas reservoirs. Non-aqueous based fluid (NAF) is frequently chosen as drilling fluids in these shale plays. While NAFs can bring benefits such as shale stabilization, lubricity, and contamination tolerance, environmental concerns and related costs are a problem. These difficulties let the operators to search for different fluid systems such as water-based muds (WBM).

Even though there is some operational alikeness, there exist a wide range of downhole conditions for shale plays such as shale mineralogy and bottom-hole temperature. Thus, a single water-based solution to aim shale plays generally is not a realistic option. Instead, a customized approach that formulates a water-based mud system for a specific shale play has been attended. Customization depend on some factors of a given shale play such as the shale morphology and lithology, drilling considerations, and other reservoir-specific variables.

In this study, two different WBMs investigated for Silurian Dadas shale formation found at south east Turkey. Full laboratory development, rheological and filtration testing are described. Additionally, the contamination and interaction of the drilling fluids systems with shale samples are examined. The experimental results shows proper rheological and filtration properties and these muds may be an alternate to NAFs with enhanced environmental and economic benefits. This study broadens our view and discusses the development of water based muds for other shale plays which have similar properties as Silurian Dadas Shale.

The economic feasibility of the exploitation of unconventional oil and gas resources is enhanced when it is possible to analyze a priori, with a reasonable accuracy, the effects of different hydraulic fracturing schemes (different fracturing fluids, different proppant concentrations, etc.) and compare them with the results in terms of the predicted production, enabling therefore the selection of the optimal alternative. Two basic ingredients for these analyses are a reliable numerical technique and an adequate geomechanical characterization of the reservoir.

The use of the Discontinuous Galerkin Method (DGM) to simulate fracture processes is discussed, with the perspective of implementing this technique to simulate the hydraulic fracturing of shale formations. It is important to remark that resulting models capture the proper fracture mechanical physics required to model nucleation and propagation of fractures.

Two examples are discussed. First, the well-known Brazilian Test is modelled; in this case the dominant phenomenon is fracture nucleation. Second, a Brazilian Test including a slot is modelled, this is a typical fracture mechanics test used for studying fracture propagation in rocks.