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The laboratory tests and Particle Flow Code numerical simulation of triaxial compression are conducted to analyze fractal dimensions of fracture surface, strength properties, energy dissipation, da...

This article, based on a keynote lecture given at the Finnish Rock Mechanics Day 2019, discusses how structured risk management can be implemented to rock engineering projects. The suggested procedure is based on ISO 31000 and a recently published methodology for practical implementation of the standard to geotechnical engineering projects. The main message is that structured risk management is a key tool to achieve high-quality rock engineering structures. A key component for many projects will be the use of the observational method to cost-effectively reduce the lack of knowledge of the ground conditions during construction of the facility. QC 20201118

Water saturation, organic matter content, and fractures are important factors influencing the physical properties of shale. In this study, shale samples were subjected to heating at 1 °C/min and then gradual cooling. An initial suite of tests was conducted at temperatures of 100 °C, 200 °C, 300 °C, 400 °C and 500 °C. The P-wave and S-wave velocities were measured, rock mechanics parameters were calculated, and then the uniaxial compressive strength test was performed. The mineral composition changed at 500 °C and the montmorillonite transformation of the shale to illite and rock diagenesis were gradually enhanced. Under the condition of heating, shale water saturation and organic matter content were reduced. The difference in the thermal mineral grain (thermal expansion anisotropy and inhomogeneous thermal expansion.) caused the corresponding changes in the internal structure of the rocks. When the changes exceeded those of the rock itself to some extent, they tended to produce microcracks within the rock, resulting in a change in the rock mechanics parameters. The results provide the fundamental parameters for rock mechanics and an important guide for high-temperature wellbore stability and hydraulic fracturing.

This paper presents a new challenge under study in Brazil: the offshore storage of natural gas and CO2 in salt (halite) caverns opened by solution mining in shallow and ultradeep water. The salt rock mechanics in Brazil started with the underground mining of sylvinite (NaCl.KCL) overlying tachyhydrite (CaCl2.MgCl2.12H2O) and research initiated in the 1970s (Costa 1984), to enable the mining of this ore. Applying a numerical simulation of drilling and excavation, the exploration and operation of mines were possible for more than 35 years. The same technology has also been used in the stability analysis of several salt caverns opened by solution mining of halite (NaCl). With the discovery of the giant pre-salt reservoirs in Brazil, underlying about 2000 m of stratified salt rocks, with the presence of tachyhydrite, all the knowledge acquired in the conventional and solution mining designs was ready to be used. More than 200 pre-salt wells have been designed and drilled successfully using the same methodology and computer codes. These approaches are proposed here as a solution to the presented challenge.

Rock mechanics projects, excavations and rock mass monitoring are day-by-day concerns of professionals and scientists of rock engineer. Technological advances observed in the 20 and 21 centuries provided high precision equipment capable of establishing deformation and estimating the rock mass stress remotely and in real time. In addition, in order to confirm and study the data obtained with theses equipment, numerical programs of modeling became more accessible to schools, research centers and private companies. Monitoring an excavation requires, besides understanding fully the rock structure, precise definitions and goals: why, how, where. This article discusses concepts of monitoring, modeling and calibration, as well as presents examples of applications where these questions were successfully answered.

Wellbore stability evaluation is one of the important applications of rock mechanics and should be regarded to prevent instabilities that may develop in the wells for various reasons (such as complex field conditions, interaction between rock and drilling fluid, directional drilling etc.). The saturation of rocks by drilling fluids causes significant changes on mechanical properties of rocks. However the level of these variations may be changed due to drilling fluid compositions. In this study, the effect of these variations on wellbore stability was examined for different well profiles. In order to assess the effect of saturation on stability of wellbores, three different drilling fluid compositions (bentonite, KCl and polymer based muds) were considered. The results of assessment suggested that the saturation by bentonite and KCl based drilling fluids create adverse effect on critical fracture and collapse pressures. However the pressure values determined as a result of saturation by polymer based drilling fluid are close to those obtained for dry condition. It should be also stated that the range of mud pressure ensuring the stability of wellbore is also significantly affected by variation of collapse and fracture pressures calculated under drilling fluid saturation.

The mineralogical composition and textural features of rocks are principal controls on rock engineering properties. A challenging rock material for engineers is represented by the evaporites, typically composed of gypsum, anhydrite and halite-rich sediments. In Abu Dhabi city vicinity, the bedrocks consist of evaporites and carbonate rocks that are partly covered by recent eolian sands and fluvial deposits. This contribution characterizes the petrographical and geoengineering properties of evaporitic rocks from Abu Dhabi city vicinity, United Arab Emirates since there are no published data available. Construction sectors in this city vicinity regularly face technical difficulties and foundation instabilities associated with evaporite bedrocks supporting foundations of buildings and infrastructures due to expansion and dissolution of evaporites. The data collected in this study includes (i) the mineralogical composition and textural features of the evaporites, and (ii) a list of geoengineering characteristics of evaporite rocks aimed to assist engineers and decision makers in resolving foundation problems at construction sites. Petrographic descriptions were obtained using polarized-light microscope, scanning electronic microscope (SEM), x-ray diffraction (XRD) and x-ray fluorescence (XRF) methods. Rock mechanical tests included Unconfined Compressive Strength (UCS), Point Load Index (PLI), Indirect Tensile Strength (ITS), Schmidt Hardness Value (SHVRB) and Slake Durability Index (SDI), performed according to the International Society of Rock Mechanics (ISRM) and the American Society for Testing and Materials (ASTM) standards. Varying degrees of correlation (weak to strong, positive to negative) exist between the geoengineering parameters, probably reflecting the influence of petrographical properties of evaporitic rocks on these parameters.

Development of equipment, which provides access to underground mineral deposits and their extraction, requires the use of all the accumulated experience and advanced scientific research in the area of mechanical rock cutting. The most important issues of using mechanical rock cutting tools are their wearability and consumption, which have an impact on technical and economic indicators of project efficiency. The paper describes Russian and foreign practices of estimating tool wear resistance, expressions to determine critical cutting speed, methods to evaluate tool consumption. It is demonstrated that wearability of mechanical tools and associated effects are to a large extent defined by rock abrasiveness. It is highlighted that in Russia the index is calculated using Baron-Kuznetsov method, which is briefly described in the paper. In many countries with a highly-developed mining industry, rock abrasiveness is estimated with a Cerchar Abrasiveness Index (CAI), recommended by the International Society for Rock Mechanics. Its description is also presented in the paper.

This paper is based on an invited lecture presented at the ARMA (ARMA-American Rock Mechanics Association) 2018 Rock Mechanics/Geomechanics Symposium, Seattle, WA. June 17–20, 2018. At the time of the invitation, the author was preparing an “Appendices” to a book (Sikora (2018) Charles Fairhurst—The Long Shadow published (via Amazon) by Itasca Consulting Group) to be published by Itasca Consulting Group—but page limitations required that the “Appendices” be eliminated. The invitation from ARMA provided an ideal opportunity to present the essence of the notes to professional colleagues. This paper attempts to expand on the presentation in Seattle. At the International Society for Rock Mechanics (ISRM) in 1962, Dr. Muller emphasized the central importance of large-scale discontinuities and anisotropy in rock engineering, and the need to establish a discipline distinct from the continuum fields of elasticity and plasticity. With the benefit of over 50 years of hindsight, it is clear that both elasticity and plasticity are important in rock mechanics—but discontinuities, especially on the scale of engineering projects, can be critical. Having been involved with the development of rock mechanics at the University of Minnesota since the late 1950s; with Professor Cundall as a faculty colleague since 1972; and with the founding of Itasca Consulting Group in 1981, the topic of discontinuities in rock has been a prominent long-standing concern to the ‘Minnesota group’. Theoretical developments in mechanics are often stimulated by experimental observations in classical ‘bench-scale’ laboratories. Thus, elasticity theory was stimulated by Hooke’s experiments (1678) and plasticity by Tresca’s experiments (1864). Even if it was possible to construct a laboratory to test ‘specimens’ of a rock mass on a scale sufficient to include large discontinuities, separation from the rock mass would remove in situ forces from the specimen, resulting in unknown changes to the specimen. What are the options to establish the constitutive behavior of the rock mass? Where is the laboratory? This paper discusses past attempts to answer this question and suggests a direction for the future.Rock in situ is unlike any other material encountered in engineering. Typically, it will vary in age from several hundreds of millions to as much as a few billions of years. Rocks of different composition and mechanical properties are often adjacent to each other. Subject to changing tectonic forces and gravity over this period, the rock mass is mechanically complex, and usually contains systems of fractures and mechanical interfaces, varying from grain boundaries to tectonic plate boundaries. Within this range, discontinuities comparable in size to the dimensions of engineering projects in rock are of particular concern to designers. The International Society for Rock Mechanics [Recently re-named International Society for Rock Mechanics and Rock Engineering. The acronym (ISRM) has been retained] was formed in 1962 to focus attention on the need to develop mechanic-based design procedures to give due consideration to such discontinuities. The paper reflects on approaches taken to address this concern in the almost 6 decades since formation of ISRM. Early efforts concentrated on testing of large physical models in a laboratory, plus a variety of efforts to incorporate discrete discontinuities into continuum mechanics. Particular attention is given to the development of the Discrete Element Method (DEM), introduced by Cundall (Proc Symp Int’l Soc Rock Mech 2:129–132, 1971). Examples of the application of DEM to practical design problems and conclusions drawn from them are discussed. In some cases, results show important differences with the current procedures and empirical rules. Although most of the examples shown are drawn from mining, references are made to applications in other engineering fields, especially Civil Engineering and recent developments in Enhanced Geothermal Systems. Currently, the principal limitation to widespread application of DEM to rock engineering design problems is computational speed. This problem is one faced in many scientific and engineering disciplines, so it is anticipated that solutions will be developed in the coming several years. In the meantime, simpler representations of discrete fracture systems are used to develop valuable general insights to inform practical designs. Recent leadership by the US Department of Energy in rock mechanics research through FORGE and SubTER [Frontier Observatory for Research in Geothermal Energy (FORGE); Subsurface Science, Technology, Engineering, and R&D Crosscut (SubTER).] offers hope that the importance of subsurface engineering to the US is being recognized. A problem, mentioned recently by Hoek (2018) that needs to be addressed in the United States is that of developing an engineering workforce capable of applying analytical and numerical techniques sensibly to design in rock.

Volume fracturing in horizontal wells represents a principal technology in the effective economic development of unconventional shale oil and gas reservoirs. However, the number of intervals that were effectively fractured by this technology only account for 20%–50% of the total designed sections. Fracture development characteristics and the factors controlling artificial fracture growth in organic-rich shale require detailed evaluation; this cannot be accomplished using microseismic monitoring technology or well-log interpretation. In this paper, formation processes of micro- and nano-scale fractures in the organic-rich shales of the Lucaogou Formation, Jimusaer Sag, Junggar Basin, northwestern China, were presented. The study focused on the application of in situ, nano-scale CT imaging technology, in combination with rock mechanics analysis. Results allowed the visualization of fracture growth in the shale reservoirs, and revealed the influence of organic matter, mineral composition, and pore structure on the formation and distribution of artificial fractures. A three-dimensional dynamic growth model of micro- and nano-scale fractures in organic-rich shale was established. Data revealed that the Lucaogou Formation shale contained dolomite and illite intragranular pores, with a low abundance of organic pores; pore size ranged between 200 nm and 2 μm. Micro- and nano-size fractures were observed. The development of artificial fractures was positively correlated with the loading stress. The initiation stress of new generated fractures was 475 mN, which could break up dolomite, albite, K-feldspar, and the original pore system as well. The original pore system was generally conducive to fracture extension and expansion. As loading stress increased from 50 mN to 515 mN, the sample extension increased from 2 μm to 14 μm, and artificial fracture width increased from 0.3 μm to 10 μm. The total porosity increased from 5.45% to 8.35%, and volume growth rate reached 53.2%. These findings provide valuable insights into the study of fracture growth in organic-rich shales, and have implications for the design of hydro-fracturing in organic-rich shales.

Proppant distribution is an important topic, because it is closely related to the success or failure of hydraulic fracturing treatment. Although, many proppant transport models have been published, there is still relatively limited research on proppant distribution between the created fracture network in shale especially during the post-treatment shut-in periods. In this paper, based on the intercoupling of particle hydrodynamics, fluid hydrodynamics, and poro-elastic rock mechanics, a mathematical model regarding the transport of liquid-solid phases has been established to simulate the behavior of the proppant transport and the carrying fluid migration in the fractured shale network during the well shut-in. The coupled model takes main hydraulic fractures, secondary induced fractures and matrix into account, namely a three-dimensional triple-porosity medium. All the important processes in fractured shale network can be explained by the liquid-solid transport simulation with the coupled model, including (1) liquid transport driven by viscous and gravity forces, (2)proppant particle transport driven by the horizontal forces of drag, inertia and collision, and the vertical gravity and buoyancy, and (3) hydraulic-fracture closure, which is considered as a poro-elastic rock deformation during the shut-in periods. Based on the conservation of mass and momentum, the liquid-solid transport coupled with rock deformation, are described by a set of partial differential equations, which are solved by the semi-implicit finite-difference method. The evolution of the proppant concentration and fluid pressure profiles is calculated. The fluxes of the proppant and proppant-carrying fluids between the main fracture and secondary fracture during the post-stimulation well shut-in are also calculated. The influences of proppant properties (concentration, density and size) and proppant-carrying fluid properties (viscosity and density) on the proppant distribution are investigated. The results of this study are expected to provide a better understanding of the proppant and proppant-carrying fluid distribution for different physical properties of proppant and carrying fluids, and explain which is the predominant factor influencing the proppant distribution during the shut-in periods.

This research was partially supported by Mining and Petroleum Engineering Department, Faculty of Engineering Al-Azhar University, Egypt, that provided machines to finish the research.

Application of modem stress analysis methods for coal pillar design require estimates of the in situ mechanical properties of coal. The yield behaviour of coal and its influence on the determination of coed pillar strength, however, is not well understood.A series of triaxial compression tests on 61, 101, 146 and 300 mm diameter samples was carried out to investigate the effects of scale on the mechanical behaviour of coal. The experimental study involved the development of specialised procedures for the characterisation, handling and preparation of the coal samples. To provide reliable and reproducible test results it was necessary to adopt a triaxial testing method that utilised techniques developed for jointed rock samples.The "inherent variability" of laboratory coal strength data was found to be related to the degree of cleating or brightness of the coal samples. Using this observed relationship, a method for estimating in situ coal seam strength based upon "indicative" intact properties of coal and seam brightness profiles was developed. The peak strength criterion for in situ coal uses the parameters σc, m and s of the Hoek-Brown empirical strength criterion for rock masses.The results of the experimental program have shown that, depending on the magnitude of the confining stress, the deformation behaviour of coal alters significantly with a change from an axial splitting to shearing mechanism of failure. The post-yield sample deformation measurements also indicated that the coal behaved in a non-associated manner. A flow rule was derived to incorporate stress-dependent dilation parameters, α and β, which are related to the Hoek-Brown parameters, m and s.The coal strength and deformation criteria were implemented in a series of three- dimensional numerical modelling experiments to estimate pillar strength. Comparisons with in situ pillar strength data are made, and the application of the criteria for different coals seams is discussed.

Tunnel construction is gradually developing to areas with high in situ stress; the deeper the tunnel construction, the more intense the earthquake disturbance. Under the background of frequent earthquakes, the seismic characteristics of tunnels become an important content related to the safety and stability of engineering structures. In view of the key problems of seismic response and vibration reduction measures for complex deep buried tunnels, the methods of advanced grouting and foam concrete aseismic are studied in this paper. Firstly, through geological survey, the in situ stress and geological conditions of the study area are analyzed. The structural characteristics of surrounding rock and related rock mechanics parameters are analyzed. The failure criterion of concrete lining under dynamic load is studied theoretically, and the relevant numerical calculation parameters are modified. A numerical model based on viscous boundary conditions is established. Through numerical calculation, the seismic response of tunnel surrounding rock and lining under different damping measures is analyzed. The research results have theoretical research value and social and economic benefits for ensuring the safety and stability of tunnel structure and improving the seismic fortification level.

Hydropower is the energy generated by transforming the force of water into electrical energy. To take advantage of this power, large hydraulic infrastructures are built that are suitable for extracting the maximum potential from this renewable, emission-free, and domestic resource. The goal of this chapter is to have an overview of the worldwide research trends related to hydropower. All publications indexed in the Scopus database with this term in the title, abstract, or keywords are studied, obtaining more than 23,000 records. The subject categories have been analyzed, and the most important ones were: Engineering, Environmental Science, Energy, and Earth and Planetary Sciences. With regard to the temporal evolution of the number of publications, two periods have been detected, up to the year 2000 and after that; the latter period has an exponential growth. In terms of countries, it has been observed that this ranking is led by China, the United States, Germany, the United Kingdom, India, and Brazil. The main institutions with at least 200 publications were 15, all from China except one from Norway. Study of the keywords made it possible to detect nine clusters that were considered significant and that establish the research trends in this field: Small Hydropower, Energy Optimization, Rock Mechanics, Dams & Reservoir, Engineering, Fish, Hydrology, Simulation, and Agriculture. In short, this book chapter provides a global overview and new research opportunities in the field of hydropower.

Usual design of building foundations is performed based on prescribed serviceability and strength criteria as laid down by various standard codes adopted by different countries. Generally, the total settlement of a foundation is described under the serviceability criterion; whereas a strength criterion is described by bearing capacity of the soil or rock underlying the foundation. Both of these safeguard a foundation from its stability and structural integrity point of view against the acting design loads that may appear during its lifetime. The important most function of a foundation is to transfer super-structure load to the underlying strata which are composed of either soil or rock or both in layers. Engineering properties of both soils and rocks vary geo-spatially in small to large scale. In view of the wide spectrum of soil/rock characteristics, the analysis and design of foundations are provided by understanding of basic soil and rock mechanics principles. Although a detailed analysis of site-specific solutions is a must for a vital and large-scale project as well as for a problematic site condition. Building codes present the most relevant guidance in design and construction of foundations. An attempt has, therefore, been made in the present study to revisit and compare foundation design methodology, by studying and investigating three popular design codes, namely Indian Standard Code (IS code), American Concrete Institute Code (ACI) and International Building Code (IBC) by the International Code Council (ICC). In this study, the basic technical information on (i) ‘general behavior of soil and rock,’ i.e., nature of soil, rock types, stability and properties along with its behavior under foundation, (ii) ‘effect of groundwater,’ i.e., the effect of underground water on foundation, (iii) ‘foundation settlement,’ i.e., foundation failure modes, (iv) ‘preventive and strengthening measures,’ i.e., improvement of bearing capacity of strata through stabilizing methods, etc., have been covered in brief.

Early attempts to predict the creep response of rock salt around underground rooms at the Waste Isolation Pilot Plant (WIPP) produced closure estimates that were one-third to one-fourth of values measured in situ (Morgan et. al., 1985). A subsequent study (Morgan, et al., 1986) of the WIPP reference elastic secondary creep model (Krieg, 1984) used to make these predictions revealed that room closures and even closure rates could be increased by reducing the elastic constants. This study also indicated that a vertical cylindrical shaft configuration could be substituted for more complicated and expensive rectangular room configurations in studying constitutive parameters for rock salt. Sjaardema and Krieg (1986) used these results to determine how much the WIPP reference value of Young's modulus E had to be reduced to increase the creep closure and closure rate of a hypothetical borehole in rock salt by factors of 3.5 to 4. They found that E had to be divided by 12.5 to produce the desired results. 12 refs., 5 figs.

Artificial intelligence (AI) is well-known as a robust technique that can support and improve the quality of human life. In the mining industry, applications of AI changed the sciences and technologies, as well as the performance of the mining industry, especially in mining and geological engineering. Smart mines were introduced and widely applied around the world with advanced technologies based on the applications of AI. This paper aims to provide a comprehensive view of AI applications in mining and geological engineering, as well as the ideas for studies in the future. The paper focuses on the published papers of AI applications in rock mechanics, mining method selection, mining equipment, drilling-blasting, slope stability, environmental issues, and relevant geological engineering. The advantages and disadvantages of AI applications in mining and geological engineering will be analyzed and discussed in detail.

Failure criteria of rock mass is the most important base for designing of surface and underground structures. However, behavior of jointed rock mass and its failure criteria are the controversial subjects of rock mechanics. Main reasons for this discussion are problems during or after the geotechnical application. However, some of the experimental and theoretical approaches are often preferred as they are practical, compatible with engineering considerations, and assist in decision-making process. On the other hand, the differentiation in the scale of the geosystem, which varies depending on the scale of geotechnical application, building process, and time, means that the failure conditions will also change. It is clear that the Mohr-Coulomb failure criterion, which is widely used in practice, cannot exactly represent discontinuous geo-environments (fractured rock) consisting of joint systems. Since the rock generally has a discontinuous character, it has been researched since the 1970s, and the Hoek-Brown failure criterion, put forth in the 1980s and modified many times until today, is widely accepted in application. Nevertheless, it is known that the empirical parameters used in this failure criteria proposed for different types of rocks are also open to discussion. In this paper, the results of the mechanical tests conducted on the previously-fissured model material, which is physically similar to rock mass are discussed. Marble samples whose grain boundaries were disturbed by cyclic thermal treatment were used as the model material. Post-failure curves of model material obtained from continuous failure state triaxial tests were compared with Hoek-Brown Failure Criteria. In conclusion, it was shown that the failure envelopes representing intergranular failure in the post-failure phase were similar and comparable to the Hoek-Brown Failure Criterion. However, it is found out that the post-failure strength in low confining stress may be lower than that of estimation by the Hoek-Brown criterion. Experimental studies have also shown that intergranular failure will develop among structural weaknesses in rock masses, and therefore the strength parameters commonly used in practice will depend on the size of geo-application.

This study presents a fuzzy logical decision-making algorithm based on block theory to effectively determine discontinuous rock slope reliability under various wedge and planar slip scenarios. The algorithm was developed to provide rapid response operations without the need for extensive quantitative stability evaluations based on the rock slope sustainability ratio. The fuzzy key-block analysis method utilises a weighted rational decision (multi-criteria decision-making) function to prepare the ‘degree of reliability (degree of stability-instability contingency)’ for slopes as implemented through the Mathematica software package. The central and analyst core of the proposed algorithm is provided as based on discontinuity network geometrical uncertainties and hierarchical decision-making. This algorithm uses block theory principles to proceed to rock block classification, movable blocks and key-block identifications under ambiguous terms which investigates the sustainability ratio with accurate, quick and appropriate decisions especially for novice engineers in the context of discontinuous rock slope stability analysis. The method with very high precision and speed has particular matches with the existing procedures and has the potential to be utilised as a continuous decision-making system for discrete parameters and to minimise the need to apply common practises. In order to justify the algorithm, a number of discontinuous rock mass slopes were considered as examples. In addition, the SWedge, RocPlane softwares and expert assignments (25-member specialist team) were utilised for verification of the applied algorithm which led to a conclusion that the algorithm was successful in providing rational decision-making., Earth sciences, Mathematics, Engineering, Applied mathematics, Geotechnical engineering, Artificial intelligence, Geomechanics, Geological engineering, Rock mechanics, Discontinuous rock slope, Stability analysis, Discontinuity network, Fuzzy logic, Multi-criteria decision-making, Weighted decision functions

Uniaxial compressive strength (UCS) and some physical properties of rock materials are very important input parameters used in rock mechanics and engineering. Samples with standard shape and dimension are used in physical and mechanical tests. However, it is difficult to determine the UCS values in case of difficult sample preparation conditions. To overcome this limitation prediction of UCS values from indirect test methods is preferred. One of the most common parameters used to predict the UCS values of rock materials is surface hardness. In this study, the usability of hardness values (HL) of selected ignimbrite, travertine and syenite rocks in the prediction of some physical and mechanical properties were investigated by using the Leeb hardness test which has much lower impact energy than the Schmidt hardness hammer has. Firstly, petrographic and some physical and mechanical properties of the samples were determined and then the HL measurements of all samples were taken. Test results were correlated and correlation equations for dry (gamma(dry)) and saturated (gamma(sat)) unit weights, apparent porosity (n(A)), water absorption (w(S)), sonic wave velocity (V-P) were presented and prediction equation of UCS from HL measurements were proposed. In the context of the study, the effect of L/D ratio on HL measurements were also investigated and minimum length to diameter (L/D) ratio of 1.5 on samples with 50 mm in diameter was suggested for consistent HL measurements.

There is no dispute about the advances in numerical modelling for rock mechanics applications following its debut in engineering science some 50 years ago. Significant strides have been made since the days of punch cards and line printers, with modelling tools now being easy to use and capable of replicating many, but not all, aspects of rock behaviour. This paper explores some common rock mechanics problems in underground mining, and how these have been addressed through numerical modelling. The described issues include pillar design, ground support, caving prediction and ground subsidence, and mining-induced seismicity. Examples of how modelling technology has evolved over the years are given, while also pointing out current gaps and limitations in the technology. Finally, an outlook for the future is presented, including some of the challenges we are facing. An increased fundamental understanding of many rock mechanics issues is still required, but eventually one may envision a deep integration of rock mechanical modelling into mine planning and production, for a more sustainable future mining.

This paper summarizes the main observations related to geotechnical properties and tool changes that characterize the different tunnel drives in a database of 33 km of EPB tunnel records from the Barcelona area. The data have been examined in detail with regard to cutting tool replacement and performance of the mechanized excavation. The database includes tunnels in soft soils, in hard and medium rocks and in mixed soil-rock conditions; tool changing records and geotechnical properties. Transverse and longitudinal geotechnical heterogeneity are accounted for systematically. Longitudinal heterogeneity is used to subdivide the drives in the database into homogeneous units. Transverse (within section) heterogeneity is described by a set of newly developed impact factors FI.

The increasing complexity of reservoirs, particularly shale reservoirs, demands accurate information on the formation composition, mineralogy, and mechanical parameters for effective exploitation. The development of geochemical and geophysical logging technology allows the investigation of the correlations between the elemental, mineral contents, and the mechanical parameters of shale. Taking the Lower Cambrian Niutitang Formation shale in the Fenggang block in northeastern Guizhou as an example, 889 data sets of the main elemental (Si, Ca, Fe, S, Ti, Gd, K, Mg, and S) concentrations and minerals (carbonate, pyrite, clay, quartz, feldspar, and mica) from Elemental Capture Spectroscopy logging and rock mechanics parameters (dynamic Young's modulus, dynamic Poisson's ratio, shear modulus, bulk modulus, and brittleness index) determined via Sonic Scanner logging data in the target zone of the study area are collected. We investigated the relationships between the mechanical parameters and the elemental, and mineral concentrations by Spearman rank correlation analysis. The influence of different Si concentrations on the mechanical parameters of the rock (positive/negative, and significance) is discussed based on the mineral contents determined via X-ray diffraction of 24 experimental samples. When 22.1%