bluuebunny/crossref_metadata_2025 huggingface dataset:
Absenteeism, Dropout, and On-Time School Completion of Vulnerable Primary School Students in Ethiopia: Exploring the Role of Adolescent Decision-Making Power in the Household, Exposure to Violence, and Paid and Unpaid Work
Authors: Woldehanna Tassew , Endale Kefyalew , Hamory Joan , Baird Sarah
Published: September 2021

While Ethiopia has seen a rapid expansion of school enrollment over the past 25 years, especially in primary education, dropout, absenteeism, and grade repetition remain key challenges to achieving the education-related Sustainable Development Goals. This article uses the 2017/18 Gender and Adolescence: Global Evidence (GAGE) survey of 6800 Ethiopian adolescents and regression analysis to examine how exposure to and /or experience of violence (from peers and at home), adolescent decision-making power in the household, and paid and unpaid child work are related to absenteeism, dropout, and on-time completion in primary school. The findings provide empirical evidence on the positive association between adolescent decision-making power in the household and educational outcomes and the negative relationships between adolescent education and both exposure to and /or experience of violence and paid and unpaid child work. We explore variations in the magnitude and robustness of these associations across gender, age cohort, and rural/urban residential location. Our findings suggest that programs which enhance decision-making power of adolescents in the household reduce exposure to and/or experience of violence among peers and at home and reduce participation in paid and unpaid child work which can improve adolescent educational attainment.
Trophic gauntlet effects on fisheries recovery: a case study in Sansha Bay, China
Authors: Xie Bin , Huang Cheng , Wang Ya , Zhou Xijie , Peng Guogan , Tao Yancheng , Huang Jiaju , Lin Xiaoqing , Huang Lingfeng
Published: September 2021

Low biological productivity causes ecosystem energy deficiency. Sansha Bay is an important spawning and nursery ground for migratory fish in the East China Sea (ECS). There is significant mariculture in this area, but stock enhancement programs and seasonal fishery closures have failed to recover populations of the commercially important species,
Larimichthys crocea
. We want to figure out the potential reason of unsuccessful
L. crocea
resource in recent 30 years. In this study, the trophic status of
L. crocea
, the food source proportions of
L. crocea
and zooplankton, and the food web structure and functioning of Sansha Bay was analyzed. A high nutrient low chlorophyll phenomenon was observed: this prevented harmful algal blooms, and phytoplankton growth was restrained by intensive macroalgal culture, resulting in a low abundance of zooplankton in Sansha Bay. Phytoplankton was the most important food source of zooplankton, and zooplankton was the greatest food source of juvenile
L. crocea
. Analyzed
L. crocea
suffered from starvation. Crucially, most of the phytoplankton was not used efficiently in the Sansha Bay ecosystem. This study suggests that trophic bottleneck, caused by food limitation, is a potential reason for unsuccessful fishery recovery in enclosed bay with macroalgal culture.
Scalar-pseudoscalar pair production at the Large Hadron Collider at NLO+NLL accuracy in QCD *
Authors: Li He-Yi , Zhang Ren-You , Zhang Yu , Ma Wen-Gan , Long Ming-Ming , Li Shu-Xiang
Published: September 2021

We thoroughly investigate both transverse momentum and threshold resummation effects on scalar-pseudoscalar pair production via quark-antiquark annihilation at the

Large Hadron Collider at QCD NLO+NLL accuracy. A factorization method is introduced to properly supplement the soft-gluon (threshold) resummation contribution from parton distribution functions to the resummed results obtained by the Collins-Soper-Sterman resummation approach. We find that the impact of the threshold-resummation improved PDFs is comparable to the resummation effect of the partonic matrix element and can even predominate in high invariant mass regions. Moreover, the loop-induced gluon-gluon fusion channel in the type-I two-Higgs-doublet model is considered in our calculations. The numerical results show that the electroweak production via quark-antiquark annihilation dominates over the gluon-initiated QCD production by

orders of magnitude.
Computational tools for the analysis of circular failure of rock slopes
Authors: Carranza-Torres C
Published: September 2021

Among other types of failure in slopes created by excavation or filling, circular (also referred to as rotational) type of failure plays an important role in the design and stability analysis of high rock slopes, such as those encountered in deep open pit mines. When a rock slope of significant height involves predominantly one type of jointed rock mass, the scale of the problem is frequently such that the rock mass (intact rock and rock discontinuities) can be regarded as a homogeneous isotropic material. In such case, if the rock slope is unstable and collapse occurs, circular (or rotational) failure as in failed slopes in soils is also observed for the rock slope. One main goal in practical design of deep open pit mines is to determine safe inclination angles for the pit faces to be excavated to avoid failure. Computational tools for quick assessment of the stability conditions, in particular determination of factor of safety and location of the critical circular failure surface, are useful during the preliminary stages of open pit design. Among others, such tools allow the engineer to gain insight in the role that the different variables controlling the problem have in defining the stability conditions for the rock slope. This paper provides first an overview of typical numerical techniques used to assess the stability of high rock slopes. For the case of slopes in rock masses that are assumed to obey the Mohr-Coulomb or the Hoek-Brown failure criteria, the paper discusses how application of transformation rules leads the criteria to be re-casted in dimensionless form, so when these are applied to the solution of slope problems, the results (factor of safety and coordinates that define the location of the critical circular failure surface) can be summarized in dimensionless compact forms. The paper presents then computational tools in the form of dimensionless charts and computer spreadsheets for stability analysis. These are developed from numerical limit equilibrium models that use the mentioned transformation rules. Among others, the computational tools allow the concept of mechanical similarity of rock slopes to be naturally introduced. Finally, the paper presents various rock slope examples that illustrate the use of the computational tools. In these examples, results from limit equilibrium models are also compared with results obtained with full numerical analysis, in particular with finite difference models implementing the shear strength reduction technique.
Elastic anisotropic behaviour related to crack distributions in two gneisses
Authors: Rotonda T
Published: September 2021

Stress-strain response of foliated rocks shows that mechanical behaviour and degree of anisotropy are influenced by the spatial arrangement of phyllosilicates. But the anisotropy of these rocks is essentially due to the characteristics and distribution of cracks aligned with mica beds. At the laboratory scale, the elastic symmetry can be represented by the transverse isotropy, with the lowest elastic modulus perpendicular to the plane of aligned microcracks. These issues are discussed with reference to experimental data obtained for two gneisses of the same geological formation. The gneisses show a quite similar strength behaviour, but very different deformabilities. The measures of dynamic and static deformabilities under loading prove the influence of the progressive closure of open cracks on the compliance tensors of both gneisses. The relationship between the elastic parameters and the characteristics of the crack distributions is discussed in the framework of non-interacting crack models. Assuming the presence of two different sets of cracks, crack densities have been estimated. The different deformabilities of the two gneisses can be ascribed to their different microcrack distributions. The degree of anisotropy due to cracks reduces as stresses increase, differently for the two gneisses.
Stability evaluation of cut slopes in highly weathered schists using limit equilibrium, kinematical and empirical methods
Authors: Janevski B , Jovanovski M
Published: September 2021

1. Extended abstract

The traditional limit equilibrium method and the kinematic analyses are the first choices in the geotechnical practice for the assessment of the slope stability of a particular rock slope. The reason is that very few empirical methods exist for this purpose.

This paper presents results of the slope stability assessment with limit equilibrium, kinematical and empirical methods for over 50 deep cut slopes in highly weathered schists along the A2 motorway section Kicevo-Ohrid in RN Macedonia. The research area is mainly composed of phyllite, sericite schists, quartz-sericite schists and graphitic schists. These rocks are highly weathered, tectonically disturbed and often folded, which means they are prone to local deformations, especially in aspects of the long-term impact of atmospheric influences and the existence of unfavourable joint sets. Although most of the failures that occurred had local character, on several cut slopes global failure occurred. The slope stability assessment of the subject rock formations is a difficult challenge because the highly weathered phyllite and schists are difficult to be characterised, considering the uncertainties associated with the material anisotropy and the network of discontinuities.

This study employs different failure mechanisms of cut slope stability in complex geological media. The rock masses were modelled according to the generalized Hoek-Brown criterion while the joints behaviour was modelled using the Barton-Bandis shear strength criterion. Rocscience software package was used for executing the limit equilibrium analyses and the stability analyses along discontinuities. The relatively new and intuitive empirical method Q-slope was applied for the stability assessment of the excavated rock slopes.

According to the results and the findings, it can be emphasized that although the limit equilibrium analyses showed relatively stable slopes, significant failures on several cut slopes occurred on site. The stability conditions on site were confirmed with the kinematical analyses and the Q-slope method.

The final decision of the slope geometry should be made after the inspection of the excavated surfaces because it is very difficult to register the discontinuity conditions before the construction phase starts. The best way to assess the stability condition is with a combination of different tools and methodologies, especially when we face highly weathered rock formations.

The next step of this research will be to propose a methodology, where the long-term rock slope stability and the associated level of risk will be evaluated using graphical diagrams.
An Overview of carbonate complex characteristics on dam sites along The Neretva River
Authors: Jazvin E , Ćpago A , Jovanovski M
Published: September 2021

1. Extended abstract

An extensive inventory of engineering rock properties presents an essential feature for characterization of the site which is of vital importance for engineering activities. Geotechnical modelling is a highly sophisticated procedure that considers number of influential factors on rock mass conditions and properties which are of particular interest in design of large, capital buildings. In specific geological environments, such as karst, it is practically impossible to obtain specific design parameters without multidisciplinary approach that involves experts in various fields (engineers, hydrologists, geologists, speleologist) coupled with the application of available technologies and methods to survey the site and foreseen possible risks for the project.

Carbonate complexes are present in the maritime and central belt of the Dinaric Alps through which Neretva River flows. In river’s central basin, Salakovac and Grabovica hydroelectric gravity dams were constructed, the case study sites analysed in this paper. In this area, numerous field and laboratory tests of mechanical and dynamic properties had been carried out. The current work is a continuation of previous studies conducted by Selimoviæ (2004) and further deepened by pago (2010) and related publications and aims to provide an overview of the practice and methods, highlight common issues and risks of designing and building in karst and to draw the lines among a spectra of rock characterization parameters used to describe carbonate complexes in Neretva River area.

Validated regression models that examine the correlation between rock properties were used to create clusters of rock mass quality and the corresponding values for static and dynamic parameters to enable faster yet sufficiently accurate input data for geotechnical modelling process for initial project stages. With each construction project in the surrounding, given dataset should be supplemented with newly obtained data that would improve the accuracy of the model and open an opportunity for development of new model types to make geotechnical analysis more reliable while deepening the understanding on local conditions for designing and building in the karst areas of Neretva.
A Modern Approach in Analyzing and Designing of Rockfall Protection Measures: The City of Omiš Rockfall Protection Case Study
Authors: Peranić J , Prodan M Vivoda , Jovančević S Dugonjić , Udovič D , Arbanas S Mihalić , Gazibara S Bernat , Krkač M , Arbanas Ž
Published: September 2021

Extended abstract

Rockfalls are the most frequent and dangerous type of landslides, generating high economic and social damages in zones built in different types of rock mass. The high danger of rockfall occurrence mainly lies in high speed of the falling rock mass that is very difficult for any fast response in the protection of human lives, settlements and infrastructure. The main part of Adriatic coast of Croatia is built in the limestone rock mass and numerous cities and traffic infrastructure were built in a narrow coastal belt, just below steep slopes of limestone massifs [1]. Numerous cities (e.g. Rijeka, Omiš, Makarska, Dubrovnik) and small settlements, as well as hundreds of kilometres of roads, are exposed to rockfall threats and their consequences expressed in human lives and economic damage. Because of the nature of a rockfall occurrence, where relatively small rockfall volume can cause extremely high damages, there were numerous projects in rockfall protection along the Croatian part of Adriatic coast last years.

One of the most comprehensive and by its volume the most important project in Croatia was the City of Omiš rockfall protection project conducted from 2006 to 2018 [2]. After the numerous rockfall occurrences that hit the City during its known history, the modern rockfall protection constructions and new technologies in rockfall analyses and protection designing enabled the development of the efficient rockfall protection systems. In this paper, we will describe the methods of field and remote sensing investigation of rock slopes, identification of rockfall sources, modelling and simulation of rockfall propagation, as well as the selection of protection measures and their positioning at the slopes above the central part of the City of Omiš. The carried out measures and estimation of their efficiency in reduction of rockfall hazard and risk in the central part of the City of Omiš will be described.
The importance of accounting for matedness when predicting the peak shear strength of rock joints
Authors: Ríos-Bayona F , Andersson E , Johansson F , Mas Ivars D
Published: September 2021

The contribution from both surface roughness and matedness in the peak shear strength of rock joints is not yet well understood. To be able to account for the influence of matedness on the peak shear strength of rock joints, both surface roughness and aperture need to be considered. Technical developments over the past few decades have shown that both surface roughness and aperture can be accurately measured using optical scanning. This technique has been utilized to account for surface roughness parameters in various shear strength criteria that assume a perfect match between joint surfaces. This paper investigates and compares the capabilities of two shear strength criteria to predict the peak shear strength of rock joints with different matedness. The analysis performed shows that both approaches have their strengths and limitations. For instance, accounting for the matedness of unmated rock joints based on their surface aperture gives better predictions of the peak shear strength. On the other hand, accounting for shearing failure mode becomes relevant at high normal loads. A possible way forward to reduce the limitations of these criteria could be to combine their strengths.
Measuring Carbonate Rock Strength using Spectroscopy across the Optical and Thermal Region
Authors: Bakun-Mazor D. , Ben-Ari Y. , Notesko G. , Marco S. , Ben-Dor E.
Published: September 2021

We seek to define new empirical relations between the spectral signature of rock surfaces and their geomechanical characteristics. By this means, proxy tools can be developed to classify the quality of rock masses in situations where access is restricted or impossible. In rock mechanics research, remote sensing technologies are mainly used for mapping surface geometry and rock discontinuities. However, the characterization of intact rock’s mechanical properties via remote sensing is a technique that has not yet been developed. In this study, spectral information is implemented using optical and thermal spectral regions. This technique enables identifying and recognizing objects based on the spectral absorption features of specific chemical attributes. In general, spectral acquisition of rocks can be done using stationary or moving (airborne) platforms. Assuming the chemical and physical attributes of rocks correlate to the material physical and chemical properties we find the spectral-based model for assessing rock strength remotely. As part of a preliminary proof-of-concept stage, we collected multiple cylindrical samples of different carbonate formations from several rock outcrops in Israel. We used point and imaging hyperspectral remote sensors to measure the surfaces of the samples in the visible and infrared regions. We determined the uniaxial compressive strength of the rock samples and analyzed them, to generate a model describing the strength of the samples, solely from spectral readings at both ranges. In addition, we conducted in-situ measurements of rock strength using a Schmidt hammer and rock surface spectra in the visible region on rock outcrops. The results of this pioneering study show that the correlation between carbonated rock strength and its spectral signatures enabled the remote assessment of the carbonate rock strength and led the way to an airborne remote sensing application. We continue to extend the database and further refine the analytical method, using this to establish a solid spectral-based model to depict rock strength remotely through exploiting the hyperspectral technology from stationary and airborne platforms.
Using non-destructive testing to assess static elastic modulus of a limestone exposed to high temperatures
Authors: Garrido M E , M-Ibáñez V , Signes C H , Tomás R
Published: September 2021

The determination of static elastic modulus in the laboratory requires rock core extraction and the subsequent testing of the samples by means of standardised uniaxial compressive strength tests. However, this destructive procedure is not always suitable – as in the case of protected historic buildings. In these cases, the static elastic modulus can be obtained from the dynamic elastic modulus, in turn derived from the velocity of ultrasonic waves (a non-invasive and non-destructive test). The relationship between both the dynamic and static moduli of rocks has been extensively addressed in the scientific literature. Furthermore, several researchers have separately studied the evolution of static or dynamic elastic moduli of rocks exposed to high temperatures – although few studies have compared both values. It is well known that the dynamic modulus is generally higher than the static modulus, and the values diverge especially in rocks with a low modulus of elasticity. These differences can be mainly explained by the effect of porosity and the size of cracks in the determination of both parameters. In this research, the relationship between static and dynamic moduli for ‘Borriol’ limestone is studied for samples previously subjected to 200, 400, 600 and 800 °C and then cooled slowly (in air) or quickly (immersed in water). The results show that the static modulus of samples heated up to 600 °C decreased 80.9 and 79.1 % and dynamic modulus decreased 62.5 and 64.8 % for slow and quick cooling samples, respectively. For samples heated to 600 and 800 °C, the static and dynamic moduli are similar. In general, no significant differences between both cooling methods are observed, even though static modulus shows more loss than dynamic modulus. Finally, linear models were used to correlate static and dynamic moduli, providing coefficients of determination of 0.99 and 0.97, for slow and quick cooling, respectively. It is also remarkable that the Edyn/Est rate was smaller than 1 for elastic moduli over 30 GPa (i.e., 105, 200 and 400 °C) and greater than 1 for lower moduli (i.e., 600 and 800 °C). The results obtained can be used to calculate the static elastic modulus of ‘Borriol’ limestone from dynamic modulus determined by non-destructive techniques.
Evaluation of the basic friction angle in dry and conditioned fluids by tilt tests
Authors: Beyhan S , Özdemir M
Published: September 2021

The basic friction angle is a basic parameter used in the shear strength estimation of discontinuities. The accurate determination of the shear strength of the discontinuities is of great importance for engineering structures built on or inside the rock.

In this study; the variation of the basic friction angle tests under dry and different fluid conditions were carried out. For this purpose, a tilt device was designed. 7 different types of travertine samples with dimensions of 10×10×2 cm were used in the experiments. Tilt tests; to determine the change of the basic friction angle under different liquid conditions, dry, pH2, pH7 and pH12 were carried out under different test fluid conditions. Basic friction angles were measured 5 times in each group experiment. Initial basic friction angles were high regardless of sample type and experimental conditions. But; as the measurements continued, significant changes were observed about slip angles. The lowest basic friction angle was obtained in samples conditioned with pH2 while the highest angle was obtained in samples with ph7 conditioned. Thus, the effect of different water contents on sliding surfaces was determined experimentally. It is thought that this study can contribute to the existing studies on the basic friction angle with the tilt test.
Photoelastic stress analysis of mode I fracture toughness tests using PMMA samples
Authors: Muñoz-Ibáñez A , Herbón-Penabad M , Delgado-Martín J
Published: September 2021

Rocks are usually inhomogeneous and anisotropic materials. The presence of foliation planes, grain boundaries or even microcracks may alter the stress distribution. In order to identify whether unusual behaviours in rocks are due to these imperfections or result from other factors (e.g. experimental configuration), the analyses of homogenous and isotropic materials is an useful approach. We have performed a series of mode I fracture toughness (KIC
) tests using polymethyl methacrylate (PMMA) samples, which has the advantage of allowing photoelastic stress analysis based on its birefringent nature. Three different testing configurations were considered in the study: S\ emi-circular bend (SCB) test, the pseudo-compact tension (pCT) test, and a new alternative configuration based on the previous two that we have called pseudo-SCB (pSCB) test. To perform the photoelastic analysis, all the experiments were complemented with a specially-designed experimental setup consisting in two orthogonally arranged circular polarizers placed on both sides of the tested specimens. Using a source of white (polychromatic) light on one end it is possible to record the stress distribution using a digital camera aligned with the samples on the other end. As the load increases, a distinct evolving pattern of colour fringes can be visualized in the samples illustrating the spatially distributed stress levels. Based on this analysis we observe in some of the tests performed non-symmetrical stress fields. Although this behaviour could be related with the testing configuration, results suggest that other features, such as the shape of the notch tip, imperfections in sample preparation, or the misalignment of the samples in the testing device may also have an influence in stress distribution.
Estimation of crack initiation and crack damage stress by means of mechanical, physical and dynamical properties in brecciated marbles
Authors: Kotsanis D , Nomikos P , Rozos D , Perraki M
Published: September 2021

The objective of this study is the determination of the various stages of deformation of brecciated marbles, under uniaxial compression, and the application of regression techniques, to investigate the relations of these stages, with physical, dynamical, and mechanical properties. Therefore, a total number of fifteen specimens, prepared from samples obtained from various locations from the southern part of the East Attica Prefecture, Greece. The laboratory program involved the determination of the uniaxial compressive strength (UCS), the crack initiation (Cci) and crack damage stress (Ccd) levels, the static elastic modulus (Es), as well as the basic physical and dynamical properties, such as the dry density (γd), the effective porosity (neff) and the ultrasonic velocities of both primary (VP) and secondary (VS) waves. Results obtained from the mechanical tests reveal that the onset of stable (Cci) and unstable (Ccd) crack growth varies between 0.19–0.38 and 0.66–0.92 of the UCS values, respectively. Applying simple nonlinear regression models, it was found that crack initiation and crack damage stresses, decrease exponentially with the increase of effective porosity, while increase exponentially with the increase of static elastic modulus, dynamic elastic modulus (Ed), and the primary wave velocity.
Stability assessment of obliquely-bedded rock cuts using multi-prong procedures – case study
Authors: Spyropoulos E , Nawaz B , Ojo A , Ahmed H R , Waheed M A
Published: September 2021

The stability of vertical cuts in rocky strata, associated with the provision of the transportation infrastructure through a mountainous terrain, is always a challenge for the geotechnical engineers. The problem becomes further complex if the cuts are parallel or near parallel to the bedding planes. Such a scenario results in all sorts of slope instability scenarios, including planar, wedge, rockfall, and toppling failure. A linear project was planned to pass through the mountainous stretches of western Saudi Arabia. The rock slopes exposed at the site after the excavations constitute igneous origin Granite/Granodiorite rock present in a moderately to highly weathered state and consist of two sets of discontinuities; one running almost parallel to slope faces and another nearly orthogonal to the major set of discontinuities. Based on the orientation of the discontinuities along the cuts on both the sides of the excavation, there is a high probability of all types of slope failures, including planar, wedge, toppling, or boulder/rockfall. This paper presents details of geologic field mapping, field and laboratory testing, and the software analysis of several modes of the possible slope failure modes. The study was carried out considering all the potential triggering factors, including rainfall, under both static and dynamic/seismic conditions. The paper also discusses the slope failure prevention measures recommended based on the interpretation of the field and laboratory data, software analysis, and the construction sequence.
Determination of frictional resistance pair Jr/Ja using a friendly – graphical approach in the Q-slope empirical method
Authors: Borja-Bernal C P , Jordá-Bordehore y L
Published: September 2021

The Q-slope index is a new geomechanical classification for slope [1] that has become popular and is spreading throughout the world. It is currently being applied in various lithologies, in different countries, mining and civil projects. The Q-slope allows engineers to adjust and optimize slope based on field observations of some geomechanical and geometric parameters that are easy to obtain. The selection of the value of each of the different parameters is made based on tables [2] some of whose parameters are the same as in the tunnel Q index, e.g. roughness (Jr), alteration (Ja), RQD etc. However, if the rock engineering has to analyse many slope with different properties, it is not so intuitive to work with very detailed tables and descriptions. We have therefore based ourselves on the concept of the graphic Geological Strengh Index [3] that uses short descriptions and designs. In this investigation we have selected the two parameters that form the pair of frictional resistance Jr / Ja (joint roughness number and joint alteration number. This Jr / Ja coefficient is very important since it is the multiplied by a correction factor for favorable or unfavorable orientation called O-factor. This O-factor is one of the novelties of the Q-slope compared to the “classic” Q of tunnels. Throughout the investigation we have simplified the descriptions of Jr and Ja (referring the reader to the previous works to know these parameters in grater detail) and created some graphic images that are easy and friendly to implement on site with a multiple choice table.
Comparison between methods for calculating the volume of rock blocks
Authors: Carriero M T , Ferrero A M , Migliazza M R , Umili G
Published: September 2021

Many methods for calculating the volume of rock blocks have been developed in the last decades. The first attempts to estimate such crucial quantity produced analytical equations to calculate the mean and variance of volume, considering blocks created by three discontinuity sets with a certain spacing probability distribution. From then, the research community followed three kinds of approaches for calculating block volume: the fully analytical one (e.g., Palmstrøm’s formula), the fully probabilistic one (e.g., Discrete Fracture Network generators), and the mixed one (e.g., In Situ Block Size Distribution). In this paper, a comparison among the different methods is presented, supported by numerical examples, highlighting their strengths and disadvantages in terms of reliability and repeatability.
Evaluating the correlation of rock mass classification systems in volcanic lithologies: a case study in a vein-shaped mining district at central Chile
Authors: Díaz R A , Arbea J A , Marulanda L Y
Published: September 2021

Defining engineering behavior of rock masses is strongly dependent on observations made in situ and the following rock mass geotechnical classification. Nowadays, the most widely used classifications are rock mass rating (RMR) and the rock mass quality (Q). Because the rock mass characterization is normally done in terms of one (or rarely more than one) of these systems, and because different mechanical assessment tools used in this and later stages of mining design are typically expressed in any of the systems, it is important to be able to properly correlate rock mass classification ratings in at least the most used rock mass classification systems. In this paper new relationships for correlation of mentioned ratings are proposed. Data used was collected from active mines at Chépica mining district, located in the Maule region of central Chile. Results are compared with similar proposals from various authors and statistically evaluated to show that the proposed correlation equation is accurate and useful when applied to volcanic lithologies with rock masses in the range of fair to good.
Variation of Drilling Rate Index (DRI) with temperature and its relationship with thermal damage on ‘Prada’ limestone
Authors: Martínez-Ibáñez V , Basco A , Garrido M E , Hidalgo Signes C , Tomás R , Miranda T
Published: September 2021

This research evaluates the variation in the Drilling Rate Index (DRI) and its relationship with thermal damage on thermally treated rocks. Samples from ‘Prada’ limestone, a lower cretaceous formation in the southern Pyrenees (Lleida, Spain), were subjected to temperatures of 105, 300, 400 and 500 °C and then cooled at a slow rate. Ultrasound P-wave velocity tests were performed before and after heating the samples to evaluate the thermal damage experienced by the rock. Sievers’ J miniature drill and brittleness tests were conducted on intact and thermally treated samples, and then resulting SJ and S20 values were combined to determine DRI. The obtained results show that thermal treatment allowed an increase of 34% in the DRI of ‘Prada’ limestone at 500 °C. DRI exhibited the same variation trend than S20, so we can conclude that thermal variation in DRI is more influenced by S20 than by SJ in ‘Prada’ limestone. We also report a strong relationship between DRI and P-wave velocity, confirming a tight dependence between the drilling performance and the thermally induced damage on the limestone. The observed substantial improvement in the drillability of the rock when heated, measured in terms of DRI value increase, could help in the advance on the development of thermally assisted mechanical excavation methods.
Processing outcrop point clouds to 3D rock structure using open source software
Authors: Liu Q , Wronski L , Danzl P
Published: September 2021

This study proposes a processing procedure to extract the 3D rock structure directly from point clouds using open source software. The basic processing involves: (1) estimating the Hough’s normal of each point; (2) converting the normal to dip direction and dip of the corresponding plane; (3) coloring each point in HSV color space according to its normal; (4) decoding the sets number using the multivariate kernel density estimators; (5) extracting and visualizing the set-based points; and (6) estimating the set-based geometric parameters and conducting stereographic projection. The result is an actual discrete fracture network aggregated with the set-based point clouds having HSV colors. From the initial point cloud to the completion of processing, we manage all data in one single file. The case studies show that the processing procedure can identify, extract, and quantify the fracture sets that have less exposed areas, which facilitates the evaluation of main risks.
In-situ shear strength testing of conglomerate formation for a large RCC dam (Koysha, Ethiopia)
Authors: Pittalis G , Delisio A , Rossini C , Millesi V
Published: September 2021

Koysha Dam, located in the Southern Nations, Nationalities and Peoples’ Region of Ethiopia, is the fourth plant of the Gibe-Omo cascade comprising Gilgel Gibe (IP=200 MW), Gibe II (IP=420 MW) and Gibe III (1’870 MW) all in operation. The plant includes a 200 m high RCC gravity dam, a gated spillway on the left bank and an open-air powerhouse housing 6 Francis turbines fed by 2 steel penstocks crossing the dam body. The right abutment of the dam is partly founded on conglomerate, composed by a variable proportion of cobble and gravel sized basalt and rhyolite-trachyte sub-rounded elements surrounded by a weak matrix of fine sand and silt particles. The geotechnical characterization of such a complex material resulted in a very challenging task due to the substantial impracticality of collecting high quality, undisturbed and representative samples. Therefore, the mechanical behaviour of the conglomerate has been assessed by means of in-situ large scale shear tests carried out into a 70 m long inspection tunnel. The test results show that in the range of selected confinement pressures (0.3 to 1.0 MPa) the conglomerate exhibits a softening behaviour. Peak friction angle and cohesion are coherent with data and empirical models presented in the literature which indicate a strong correlation between volumetric block proportion and mechanical properties of the Block-In-Matrix (BIM) rock.
Geomechanical behavior evolution of the rock mass involved in the Arteara rock avalanche, Gran Canaria, Canary Islands, Spain
Authors: Antón-Bayona L M , Rodríguez-Peces M J , Yepes J
Published: September 2021

In Arteara (Canary Island), a Holocene rock avalanche comprises accumulation of large reddish blocks which cover the Fataga ravine. This course, is entrenched into the Phonolitic Formation, an alternating sequence of lava flows and ignimbrites. The avalanche defines an elongated deposit of variable thickness. A low friction angle was deduced, which is related to an easily weathered bedrock favorable to the rolling of the blocks. The movement would have been a dry granular flow with a component of saltation at the head and of turbulent flow at the intermediate and distal areas. The deposit varies widely in size and is structured in bands of blocks with a polymodal distribution and low selection. The geomechanical properties of the rocks involved vary substantially in each block and along a longitudinal profile of the deposit. Schmidt Hammer rebound measured in 233 blocks show a polymodal dispersion. Some facies have been differentiated in the blocks, not only by their appearance, but also by their rebound index (R). The different hardness reflects the differences in density and porosity. The hardness zoning shows the differential weathering of the blocks, which depends on the rock anisotropy and the flow turbulence, which determines the influence of abrasion and punching of the blocks. The rebound shows a direct correlation with the bulk density and an inverse correlation with the distance to the source area.
Heterogeneity of in situ stress: A Review
Authors: Javaid M A , Harrison J P
Published: September 2021

Campaigns to determine the state of in situ stress form an integral part of almost all underground rock engineering projects, but stress measurements obtained at different locations on a project site generally display spatial variability. However, there is no international consensus on techniques to objectively quantify such spatial variability, and the nebulous description of “stress heterogeneity” is often used. Our review shows that there are no consistent and universally agreed definitions for stress heterogeneity: the existing definitions are overly simplistic and lack a robust statistical treatment of variability in stress tensors. We demonstrate that stress data can be partitioned into homogeneous stress domains using the k-means algorithm in multivariate stress space, and the resulting clusters characterised using multivariate statistics. This allows us to propose a clear and unambiguous definition of stress heterogeneity. Our analyses also suggest that completely meaningful partitioning of stress data requires development of new algorithms and cluster validity indices.
Approaches for the digital measurement of rock mass discontinuities
Authors: Pack G , Kieffer D S , Metzler I , Liu Q
Published: September 2021

Rock mass characterization plays an essential role in rock engineering activities. Presently several approaches for digitally measuring rock mass discontinuities are available. This study summarizes some of the main technological approaches, together with comparative quantitative evaluations of discontinuity measurements. For the steeply inclined Engelswand outcrop in Tyrol, Austria, an Unmanned Aerial Vehicle was used to acquire a series of photographic images in order to generate a true color georeferenced point cloud and derivative 3D models. Discontinuity orientations were measured by manual, assisted and automated digital approaches. Orientations of individual discontinuity planes and the statistics of the overall discontinuity structure were evaluated. The manual and assisted measurement methods provide compatible results and are considered highly relevant in the context of rock engineering. While automated measurement methods are able to provide an overall indication of the dominating discontinuity pattern, discrimination of individual discontinuity sets is not feasible. While this is a major limiting factor in terms of extracting useful data for rock engineering practice, a dual digital measurement approach is considered prudent when large data sets are being evaluated. This involves conducting rapid automated measurements to obtain an overall representation of the rock mass structure, followed by supplementary manual or assisted measurements to more precisely extract pertinent structural data.
Some aspects of andesitic Bimrock characterisation
Authors: Jovanovska T , Angelova E
Published: September 2021

This paper describes an approach applied in the design and construction of one cut at section km 23+200 - km 23+400 from the expressway A4, section Stip – Radovish, part of the Macedonian road network in construction. The cut is constructed in volcanogenic rock mass of andesitic type, with different zones within the massif. It is specific, because of different phases of extrusions along wider fault zones, rock mass has typical composition of block - in -matrix (BIM) rocks. In the frame of this article, the approach based on the integral application of empirical – analytical, and observational methods during the design and construction is presented. Some results from investigations and correlations between the investigated parameters necessary to define optimal slope protection elements are also given. One attempt is done to prepare a simple tool for characterization of BIM rocks initially named as BIMSI (Block In Matrix Strength Index), based on a combination of Volumetric Block Proportion and Strength Ratio of significant blocks and matrix. This idea requires further study. Finally, some elements of applied solution for slope protection are presented.
Method for estimating rockfall failure probability using photogrammetry
Authors: Uotinen L , Janiszewski M , Mishra R , Munukka H , Szydlowska M , Martinelli D , Dabove P
Published: September 2021

Passageways cut through rock might be subjected to rockfalls. If a falling rock reaches the road area, the consequences can be disastrous. The traditional rockfall risk assessment method and risk mitigation are based on on-site investigations performed by a geologist or a rock engineer. The parameters resulting from the investigation, such as discontinuities, orientations and spacings, potential rockfall initiation locations, slope geometry, and ditch profile, are either measured or estimated. We propose a photogrammetry-based method for estimating the probability of failure for rockfall. Several photographs of the rock-cut are taken, and a 3D geometry is computed using photogrammetry. This model already allows remote visual inspection of the site. The information about joint planes can be discovered semiautomatically from the point cloud. Next, the probability of rockfall reaching the road area is computed using probabilistic kinematic analysis on the geometry extracted using photogrammetry. The results can be used to define the rockfall probability for each rock-cut. Furthermore, the results can be used to determine the appropriate rockfall risk mitigation actions for each rock-cut.
Characterization of joint roughness using close-range UAV-SfM photogrammetry
Authors: García-Luna R , Senent S , Jimenez R
Published: September 2021

The Structure from Motion (SfM) photogrammetric technique has emerge as an efficient alternative for remote 3D rock mass characterization, compared to laser scanner (LiDAR) or stereoscopic photogrammetry, due to its economy and ease of use. In a similar way, the recent development of the drone-based technology has turn UAVs (“Unmanned Aerial Vehicles”) in a more accessible device for field applications in geotechnical engineering; allowing the acquisition of high quality images from a safe distance and without the need to stablish direct contact with the rock mass. However, the close distance applicability of UAV-SfM photogrammetry has not yet been investigated in detail to characterize joint roughness at close range (<10 m). In this work we employ the SfM technique for the generation of 3D models of the joint surfaces from aerial images taken at a relatively short distance from the slope (10, 7.5, 5, and 2.5 m). Roughness profiles are extracted from the 3D data, and their Z2 statistical parameter is used to estimate the Joint roughness coefficient (JRC). Finally, the JRC value of those profiles-obtained with the UAV-SfM approach-have been compared with those obtained with traditional measurements based on manual methods. The proposed methodology is applied to a real case in an ancient open-cast mine in Northern Spain. The results obtained at different distances are compared to analyze the potential of UAV-SfM photogrammetry to develop accurate close-distance models. Results show that it is not necessary to get too close to the slope in order to get the best results, as this may cause overestimation of the JRC value.
Study of the rock masses’ fractures through OPTV (Borehole Digital Optical Televiewer)
Authors: Berlinghieri M , Pandolfi O
Published: September 2021

The article describes an innovative survey methodology through the use of optical survey camera OPTV (Borehole Digital Optical Televiewer). This camera allows us to record the borehole wall colour image at 360° and to keep the orientation with respect to the North. Through the use of OPTV surveys, the fractures present in the rocky mass can be recognized via means of sinusoidal curves readable on the image. From the abovementioned curves, it is then possible to assume the inclination, immersion, and thickness of the discontinuities. Furthermore, from the virtual core, it is possible to analyze the lithological changes and the commodities varieties characterizing the site. On the basis of the above-mentioned information, 3D models can be then created through innovative technologies, so to visualize the geological and geotechnical models in an easier way to read and understand. The mapped fractures can be integrated with the most modern techniques of Discrete Elements Numerical modeling, utilizing the dimensions, orientation, and positioning values during the model realization phase. Through practical examples of representations of the collected data, the survey methodology is described in detail in the article, together with the used technologies and the potentialities of the acquired information exploitable during the interpretation phase. The proposed methodology approach allows a better digital management of the data, encouraging a more completed and easier usage of the information with clear application potentialities in the field of rock mechanics and when facing geotechnical challenges.