bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt weathering and ultrasonic pulse velocity: condition assessment of salt damaged porous limestone
Authors: Rozgonyi-Boissinot N , Khodabandeh M A , Besharatinezhad A , Török Á
Published: September 2021

Salt weathering is one of the crucial causes of building stone decay. For assessing the durability of stones against salt weathering, a standardised test procedure (EN 12370:2020 Determination of resistance to salt crystallisation) is used: the mass loss of the stone is measured during sodium sulphate crystallisation cycles. Porous, Miocene limestone test specimens collected from the Sóskút quarry (Hungary) were subjected to salt crystallisation cycles in laboratory conditions. The limestone with open porosities of up to 32 V% is composed of ooids, various types of bioclasts and other carbonate grains. Besides the classical measurements of mass changes, the ultrasonic pulse velocity was also recorded after each crystallisation cycle. The ultrasonic pulse velocity values of quarry stones and salt-laden porous limestone specimens were compared. The results indicate that when salt crystal clogs the pores, an increase in ultrasonic pulse velocity is observed. Additional salt crystallisation cycles reduce the pulse velocity. This negative shift in pulse velocities is linked to the opening of micro-cracks, indicating the damage of the studied limestone. Our tests have proved that ultrasonic pulse velocity testing device can detect salt crystallisation damage in a non-destructive way. Its application is recommended in the condition assessment of salt damaged stone heritage structures.
Correlation between various mechanical properties of porous limestones from Hungary
Authors: Rozgonyi-Boissinot N , Pápay Z , Török Á
Published: September 2021

This study focuses on the mechanical parameters of Miocene limestones from Hungary. Four different lithotypes of porous limestone from two localities were analysed in laboratory conditions. These lithologies have been widely used for centuries as construction material in Central Europe. One type of the Badenian Leithakalk limestone, which is a bioclastic grainstone containing molluscs, foraminifera and Lithothamnium and three types of Sarmatian porous limestone; a fine-grained, medium-grained and a coarse-grained bioclastic lithotype were compared in laboratory conditions. Bulk density, water absorption, apparent porosity, uniaxial compressive and tensile strength tests were performed to obtain data set for correlation analysis. With water saturation under atmospheric pressure, the uniaxial compressive strength and tensile strength of all studied lithotypes were reduced significantly. A good correlation between dry bulk density and apparent porosity was found for two lithotypes; meanwhile, for the two other lithotypes a less significant relationship was found. Bulk density correlates with uniaxial compressive strength and with tensile strength for all lithologies. However, a significant difference was found in the coefficients of determination of the different lithotypes. The coefficients in air-dry conditions were over 70%, but they became smaller after water saturation. According to these results, microstructure, porosity, and water saturation influence porous limestones’ damage mechanism.
Design aspects of segmental tunnel lining in difficult rock conditions
Authors: Osgoui R R , Quaglio G , Poli A , Carrieri G
Published: September 2021

Despite plenty of research studies in design of segmental tunnel lining, there have still been serious concerns in damage mechanism of segmental lining in weak rock masses. With significant increasing of mechanized tunnelling practically in all kind of ground, including highly weathered rocks, severely jointed rocks, shear, and fault zones, squeezing, and swelling prone conditions, the need to investigate the mechanical behaviour and the damage mechanism of segmental tunnel lining is unavoidable. Any misjudging of those adverse geo-conditions may often cause an irreversible economical loss in the tunnelling project. This paper deals with the significant design aspects of segmental lining for such difficult rock mass conditions which can cause lining deformation and failure in segment in terms of either compression or tension as well as in the segment joints. Further, some critical design aspects extracted from the tunnel T26 of Ankara – Eskisehir high speed railway are presented and analysed.
Application of Spatial Multi-Criteria Analysis (SMCA) to assess rockfall hazard and plan mitigation strategies along long infrastructures
Authors: Foria F , Miceli G , Tamburini A , Villa F , Rech A , Epifani F
Published: September 2021

Long infrastructures often cross areas with a high probability of landslides, causing eventually serious problems to the serviceability and compromising safety. The identification and prediction of hazardous zones are difficult, especially for what concerning rockfalls, as they can occur quickly and suddenly. In order to assess rockfall hazard, detailed data such as slope geometry, geotechnical and geomechanical properties of materials, drainage system pattern, etc. are needed. Even though thematic datasets are available and easily downloadable for the majority of the Italian territory, their scale is not adequate and ad-hoc input data must be gathered. An original multi-disciplinary procedure (GEO4) has been developed by the authors based on a mobile mapping system (ARCHITA) integrated with Airborne Lidar and ILI (In-Line Inspections), geomatics, geological models, geotechnical-geomechanical characterization and geomorphometric approach. A Spatial Multi-Criteria Analysis (SMCA) is then used to create a composed and spatially distributed index of landslide hazard based on normalized values of triggering factors. Such index is used to identify and classify the morphological unstable element along the infrastructure, supporting decision-makers in defining the most appropriate mitigation measures and planning their implementation in a clearer, more repeatable and more objective orientated-way. The presented method has been successfully applied so far to hundreds of km of railway lines in Italy.
A case study on the design, numerical modelling and preliminary testing of tension piles in weak rock
Authors: Jackson P , Olbekk E , Petrella F , Wudzka A , Zanetti P
Published: September 2021

Over the last twenty years several major tunnel projects have been constructed in the Copenhagen area in the Danian limestone, either in the Copenhagen Limestone or in the Bryozoan limestone; in parallel, developments have been made in the characterization of these rocks. The Danian limestones are weak sedimentary rocks with highly variable properties in terms of their strength, stiffness and in their mass permeability. Their properties are governed by their genesis resulting in a large variation in the carbonate content, their induration and a large variability of the fissuring and distribution of fissuring. The paper describes the experience gained from selected underground construction projects in the Copenhagen area, specifically for the passive uplift anchors/tension piles that are often uses as a means to resist uplift forces resulting from the porewater pressure exerted at the underside of the base slab of major underground structures. While tension piles are common in Copenhagen, as they are often used for basement construction too, the authors are not aware of a documented calculation method. The paper presents a summary of the case histories published for ground anchors in Danian limestone and proposes a calculation method for the unit shaft resistance of small diameter tension piles as well as the comparison with numerical modelling and preliminary testing undertaken for the Sydhavn metro in Copenhagen.
Stability assessment of rock slopes combining Slope Mass Rating and Qslope classification systems: A case study in Cerro San Eduardo (Guayaquil, Ecuador)
Authors: Macías A M , Vera D K , Borja C P , Jordá-Bordehore L
Published: September 2021

In the present study, the stability of the slope located in the Modesto Apolo Ramírez Avenue, is analyzed. The avenue is located prior to the access to the Cerro San Eduardo tunnel, which has had habitual problems of falling blocks to the roadway. For the study, empirical methodology was applied, including the data mapping based on geomechanical classifications such as Rock Mass Rating (RMR), Slope Mass Rating (SMR) and Q-Slope index, which assign a defined score, obtaining the quality of the rocky mass, and with this, the degree of stability of the slope. In addition, through the application of RocFall software, the empirical methodology has been compared with the analysis of rockfall trajectory, making a retrospective study of behavior and simulating the constant falling of blocks on the roadway.

As a consequence of the exploration, it was evident that the geomechanical classifications-in this particular caseare not completely effective to determine the degree of stability of the massif. This is due to the fact that, even though the slopes are globally stable, these classifications do not seem to adequately determine a level of risk against rockfalls, as can be seen from visu. Therefore, it can be seen that the slope does not have a risk of collapse, but instead presents a high danger of landslides that could cause considerable economic and human lives losses. The study recommends geometric solutions for impact mitigation to prevent future damage.
Sustainable Shotcrete with Crushed Waste Glass
Authors: Serati M , Malgotra G , Jackson N , Basireddy SMR , Asche H
Published: September 2021

There is an ever-increasing amount of waste glass generated worldwide that is currently sent to landfill, and has a high potential for re-use. In Australia alone, the consumption of glass is 1.36 million tonnes, with the state of New South Wales producing the highest amount. Traditional landfilling and stockpiling of waste glass are not an environment-friendly solution, and the re-use of waste glass has become an important research topic in Australia and worldwide. This Project employs an experimental study to estimate waste glass re-cycling in shotcrete production. Mechanical strength and fracture properties of the new mix designs are compared against the controlled mixes at 0% waste glass inclusions. From the results, no impaired performance was recorded by substituting sand with crushed waste glass even at a high percentage ratio of up to 100%. While further research is needed, the promising early results highly encourage the applicability of crushed waste glass for sustainable shotcrete design, a topic that is yet relatively under-researched.
Solving the problems of exploitation safety of potassium salt deposit based on joint application of geophysical and geomechanical studies
Authors: Kashnikov Yu A , Shustov D V , Ermashov A O , Lebedeva O O , Zhukov A A , Prigara A M
Published: September 2021

The reliable determination of the physical and mechanical properties of the rock is one of the major issues of geomechanical modelling. It is needed to ensure exploitation safety in underground mine. This is especially relevant for the huge potassium salt deposits which uniqueness is the presence of the watered rocks that lies above the exploiting potassium seams. Particularly, a part of the rock mass that lies between potassium seams and watered rocks is called waterproof strata (WPS). The highest risk is the presence and propagation of the cracks in WPS through which the above-water can probably enter the openings that could lead to the total flooding of the mine. In order to prevent it and to provide exploitation safety the joint application of geophysical and geomechanical studies is suggested. In this paper 2D mine seismic investigations and geomechanical studies are described. And, as the conclusion, the analysis of the stress-stain state of the rock mass and its potential weak zones are presented.
Combining active and passive acoustic methods to image hydraulic fracture growth in laboratory experiments
Authors: Momeni Seyyedmaalek , Liu Dong , Lecampion Brice
Published: September 2021

We combine active and passive acoustic measurements to improve the spatio-temporal imaging of hydraulic fracture growth performed under true triaxial confinement in the laboratory. 64 active piezo-electric transducers (54 P waves, 10 S waves) work in source (32) - receivers (32) mode to perform an acoustic survey at repetitive intervals (every 10 seconds) during a hydraulic fracture growth experiment. The analysis of the evolution of the active acoustic monitoring changes allow to image the evolution of the fracture front (via an inversion of the active acoustic waves diffracted by the fracture front). An additional 16 piezoelectric transducers are pre-amplified and work in passive mode continuously recording at 10MHz. We present a nearly-automatic passive signal processing, acoustic emission detection, and location algorithm. This allows to record, detect and to locate acoustic emissions associated with fracture initiation and growth in between the active acoustic measurement sequences. Using a hydraulic fracturing test performed in gabbro, we discuss how active and passive acoustic monitoring complements one another and bring different type of information on hydraulic fracture growth.
A Thermo-elasto-plastic Evaluation of Stress State of Mars
Authors: Aydan Omer
Published: September 2021

There is recently an increasing interest to explore the ways to find out the characteristics of other planets and possibility of exploiting their mineral resources. The images sent to Earth from Mars exploration rovers showed that rocks and geological and tectonic structures are strikingly similar to those in Earth. In this study, the stress state of Mars is investigated using a spherical symmetric body concept together with the consideration of a thermo-elasto-plastic behaviour of the Earth’s constituting materials on the basis of the previous investigation of the stress state of Earth by Aydan [1,2,3]. Fundamentally four different situations, namely, fluid, elastic, elasto-plastic and thermo-elasto-plastic have been considered and the computational results are presented and their implications are discussed.
Construction works above cavities, investigation of an undermined area
Authors: Zenah J , Görög P
Published: September 2021

Construction work above previous mining area is always a great challenge from the engineering point of view. In the southern part of Budapest, the previous mining activities resulted more than a hundred thousands of square meters of cavities. These cellars cut into porous limestone with different depth, but mostly close to the surface; nowadays, these cellars are located inside a residential area, and some part of the undermined area is planned to build because this is an empty and valuable area. For the construction of these improvements, it is necessary to perform detailed investigations and stability calculations. This paper is introducing the detailed investigation process of a significant cellar which will be involved by construction activities. Three buildings are planned to build above it. The studied cellar located in the 22nd district of Budapest, Hungary, with a depth between 4.3 – 7.7 m, with a wide range of pillars’ width between 0.73 – 7.7 m according to the studied cross-sections. The investigation starts with geometrical measurements and core drillings to map the rock mechanical properties of the host rock. Several laboratory tests were done for obtaining rock mechanical parameters for modelling. After creating the geotechnical model, it was used for FEM calculations using RS2 software. Four cross-sections were chosen across the cellar system in different locations and various directions modelling the surface load of the planned building. The stability of the cellar was studied from two different viewpoints: firstly, the factor of safety was determined, and secondly, the settlement was calculated as an effect of the surface load. A displacement measurement system was set up in several cross-sections of the cellar to compare the calculated and real displacements in the future.
The numerical modeling of heterogeneities by the finite element method in 3D setting
Authors: Dmitriev S , Semenova I , Shestov A
Published: September 2021

The paper proposes a variant of the algorithm for 3D numerical simulation of the rock mass stress-strain state in the vicinity of structural heterogeneities by the finite element method. Modeling of the stress-strain state is used, among other things, when analyzing the fractures in the rock mass, which can occur as a breakage or a shear along the weakening planes. The rock massif has a block structure, where the boundaries of various-scale blocks are structural disturbances of different orders. The surface planes of structural heterogeneities usually have complex geometry and spatial orientation, so the most adequate results can be obtained by 3D modeling of the disturbed rock mass. Besides, it is important to take into account the type of the stress-strain state, which can be not only gravitational, but also gravitational-tectonic, including horizontal loading of the rock mass. Accounting these features allows obtaining the most adequate geomechanical model of the studied object. For this purpose, the authors have studied and analyzed the existing approaches to modeling heterogeneities in the rock mass, including using the Goodman contact element, and developed its 3D modification. A mining engineer needs to have a handy tool that allows creating and editing a geomechanical model, taking into account mining plans and related sections. The model navigation, edition of its individual blocks to specify geology and creation of local sub-models make it necessary to use structured meshes of finite elements. Modification of the model with the introduction of contact elements entails the creation of an unstructured mesh, which complicates further manipulations with it. To solve this problem, a special zero element was developed, which allows saving a structured mesh format when implementing a contact element. This zero element, like the contact element, has zero thickness, and its nodes have averaged strength characteristics of adjacent blocks of the undisturbed rock mass. The result of these studies is a tool that allows creating 3D models of the rock mass stress-strain state, taking into account its structural heterogeneities and preserving the regular structure of the finite element mesh.
Preliminary study on PFC3D microparameter calibration using optimization of an artificial neural network
Authors: Kim J , Choi J W , Song J J
Published: September 2021

Microparameter calibration for matching macroscopic responses of particle flow code 3D (PFC3D) models is generally conducted through trial-and-error which is inefficient and time-consuming. Several automatic calibration methods have been proposed but they are still limitations in the number of calibratable microparameters, range of macroscopic responses and degree of freedom in user-defined constraints. To overcome such limitations, a novel calibration method is proposed utilizing the constrained optimization of an artificial neural network (ANN). The ANN is trained with 600 PFC3D simulations to predict the unconfined compressive strength (UCS), Young’s modulus (E) and Poisson’s ratio (v) of a PFC3D model for a given set of 15 microparameter values. Unlike other ANN-based DEM calibration methods, the proposed method calibrates microparameters by optimizing the ANN inputs rather than obtaining the calibrated values as the ANN outputs. The integration of a PFC3D-mimicking ANN with constrained optimization enables microparameter calibration for a wider range of microparameters, macroscopic responses and a higher degree of freedom in user-defined constraints.
Piezoelectric effect does not contribute in thermal drilling of quartz bearing rocks
Authors: Saksala T
Published: September 2021

This paper presents a numerical study on a possible piezoelectric effect in thermal drilling of Quartz bearing rocks. For this end, the governing piezoelectro-thermo-mechanical problem is solved with the finite element method. The granitic rock material, consisting of Quartz, Feldspar and Biotite minerals, is taken as linear elastic but heterogeneous and anisotropic. Temperature dependence of material properties is neglected. The simulation demonstrates that the secondary stresses arising from converse piezoelectric effect are three orders of magnitude smaller than the primary thermal stresses, which means that the piezoelectric effect is negligible.
A thermo-mechanical numerical approach for the analysis of a historical rockslide in the Italian Alps
Authors: Morcioni A , Apuani T , Cecinato F
Published: September 2021

In this work, a thermo-mechanical (TM) numerical approach is presented and applied to investigate the stress-strain evolution of an alpine rock-slope located in the Central Italian Alps (Sondrio Province). Along the “Cimaganda” slope a massive rockslide event occurred around 900 A.D. mobilizing an estimated volume of 7.5 Mm3 of material, and reaching the bottom of the valley. Interest in this historic event was raised again in recent times, as a new rockslide took place in 2012, mobilizing 20.000 m3 of rock material and blocking the SS36 National Road.

To understand the general evolution of the Cimaganda rock slope, the recent geomorphological history of the Valley (post Last Glacial Maximum) was considered. In particular, to explore how glacial loading and unloading, associated with thermo-mechanical processes can promote rock mass damage, a 2D DEM numerical approach was adopted, calibrated upon the collected experimental and field data, and supported by a 2D FEM analysis to simulate transient heat diffusion over the Valley cross-section due to ice retreat and paleo-temperature evolution. Results show a clear relation between TM stresses and the occurrence of rock-mass damage and slip propagation along discontinuities. Simulated displacement and the development of a deep region of shear strain localization, allow to highlight the significance of temperature influence in preparing the rock slope to instability.
Comparison of depth-averaged and 3D models for dense granular flows
Authors: Pasqua A , Leonardi A , Pirulli M
Published: September 2021

Debris flows are one of the major threats to mountain communities. They consist of the downslope flow of fine and coarse material, saturated with water, along channelized paths. Due to their high velocity and unpredictability, the evacuation of hit areas may be difficult to execute. To avoid casualties and economic losses, mitigation structures, like filter barriers, are therefore usually adopted. Their primary task is to reduce the flow energy and to retain larger boulders. However, considerable room to improve the design of these structures still exists. In particular, gaining a better understanding of debris flows dynamics is a necessary step to improve the design of barriers. Numerical modelling can contribute to its understanding, and in an effective simulation of the flowing mass dynamics and impact against mitigation barriers. In this frame, the continuum-based Depth-Averaged Modelling (DAM) has been widely used since the 90s. In spite of the good results of this approach, together with the low computational time, the averaging procedure of velocity and pressure along the flow depth causes the loss of crucial information, which is important for correctly simulating the interaction with mitigation structures. A full 3D modelling can overcome this shortcoming by allowing a more complete flow representation, and a more accurate computation of impact forces. However, since debris flow may run for long distances, 3D models would require a large computational time. In this work we aim to study both the shortcomings and the advantages of the DAMs and 3D models. In particular, The DAM model used is DAN-W, while the 3D model is based on the lattice-Boltzmann method. To compare the results from numerical modelling, we use the experimental work performed by Moriguchi et al. (2009) in which a mass of dry sand flows on a steep chute.
Insights on squeezing behavior from Saint-Martin-la-Porte galleries
Authors: Liu Y , Sulem J , Subrin D , Tran-Manh H , Humbert E
Published: September 2021

In the context of the Saint-Martin-la-Porte survey project of the Lyon-Turin railway link, an access gallery (SMP2) was first excavated across a Carboniferous formation, where tectonized productive Houiller was met at a depth of 300 m. It exhibited a highly squeezing behavior, characterized by large, time-dependent and anisotropic deformation. Recently, a new survey gallery (SMP4) began to be excavated along the axis of the future base tunnel at a depth of about 600 m. Squeezing conditions have been met again when SMP4 crossed the same Carboniferous formation. Practical problems have been encountered related to the large and anisotropic closure of the cross-section and the instability on the tunnel face. On the basis of previous studies and numerical analyses of carried out for SMP2, the proposed methods are extended to SMP4 conditions. Numerical modeling is performed using FLAC3D code and the various phases of excavation and specific support installation are considered. The efficiency of the compressible elements in reducing the stress in the support system is demonstrated.
Stability modeling of complex underground mine openings integrating point clouds and FEM 3D
Authors: Agliardi F , Castellanza R , Frigerio G , Orlandi G M
Published: September 2021

The stability analysis of underground mine systems with complex 3D geometry is still a challenging task, especially when abandoned mines are planned for new uses with public access, that imply more restrictive safety requirements. This inherently multi-scale problem requires both the evaluation of the global mine stability and the assessment of local deformation and failure mechanisms of individual pillars or roof sectors in a robust 3D modeling framework. We integrated 3D remote survey techniques and FEM 3D modeling to perform a comprehensive stability analysis of an abandoned fluorite mine system in the central Southern Alps (Italy), including ten levels excavated in bedded limestones. We reconstructed the 3D geometry of three levels undergoing a reuse plan, combining a dynamic LiDAR system and close-range photogrammetry. We used point clouds in a workflow to generate solids, excavate the 3D analysis domain and generate a FEM 3D mesh for numerical modeling. We performed a series of continuum-based FEM 3D simulations of mine excavation and rock mass strength degradation. Our results allowed assessing the global stability of the abandoned mine and identifying critically stressed roof sectors and pillars to prioritize the local-scale analysis, remediation and monitoring of critical spots.
The driving force of all nature. Modelling water pressure and its stability consequences on alpine bedrock slopes
Authors: Scandroglio R , Stoll V , Krautblatter M
Published: September 2021

Hydrostatic pressure is one of the most important but still not fully understood destabilising factors of bedrock slopes. Water presence has often been recorded in major rock failures like at Piz Cengalo in 2017 but still its quantification and its effective destabilizing role remain unsolved issues in rockfall forecasting. Intensification of rainstorms due to climate change will enhance hydrostatic pressures in fractured bedrock, which will likely lead to increase in rockfall activity and connected risks for humans and infrastructures. Here we present a hydro-mechanical stability analysis of the Hochvogel summit (2,592 m AA) in the Northern Calcareous Alps. At this site, an imminent high-magnitude rockfall could destabilise up to 260,000 m3 and is therefore acutely monitored. Displacement measurements on the summit showed daily acceleration following intense precipitation. With the help of direct investigations and laboratory tests from previous studies, we implemented the Hochvogel SE slope and its mechanical parameters in the 2D Universal Distinct Element Code (UDEC). Our model shows that the presence of water columns of 10 m decreases the factor of safety (FoS) on average by 11 % and can increase the max displacement by up to 70 %. When including the effects of cleft weathering in the model, FoS < 1 can be reached. The friction angle of clefts has a key role in this destabilization process. This study provides key elements for interpreting the mechanical behaviour of this imminent rockfall in connection with hydrostatic pressures, helping to improve hazard forecasting at the Hochvogel and at similar sites.
Three-dimensional Distinct Element Method for stability analysis of marble quarries in the Apuan Alps (Italy)
Authors: Berlinghieri M , Pandolfi O
Published: September 2021

The present article analyses and proposes an innovative dynamic planning methodology, supported by computer tools and in-situ measurements, for the optimization of the planning techniques of underground marble quarries. The abovementioned planning methodology has been implemented in ‘Cava Piastreta’, an underground marble quarry located in the Apuan Alps, Italy. The entire excavation area has been characterized with tridimensional topographic surveys, geotechnical traditional surveys, and radar surveys, as well as stress-level measurement campaigns through a CSIRO cell. When an underground excavation project concerning stone material is designed, it is mandatory to have an instrument allowing a forecast of the stress-strain behavior of the rock mass. To this end, the rocky outcrop can also be represented by different mathematical models to schematize the geomechanical behavior. The accuracy and reliability of the simulation of the mechanical response of the fractured mass depend on the exactness with which the rocky outcrop is defined. Therefore, the geometric modeling phase acquires prominent importance. To better address the discontinuous nature of the studied rocky mass, the distinct element method has been used in modeling the mechanical behavior of the mass itself. Given the peculiar geometrical characteristics of the excavation site in question, the deterministic approach has been chosen to simulate as closely as possible the position of the major discontinuities identified in-situ. The present article thus aims to briefly describe a study that has been developed over the last years intended to deepen the analysis of the geostructural characterization of the excavation site, as well as to compare the obtained results through the geometrical tridimensional modeling with the values measured in-situ.
Assessment of collapse mechanism of a High Speed Railway Tunnel (T341 Tunnel, Turkey)
Authors: Aygar E B , Gokceoglu C
Published: September 2021

Excavation and implementation of tunnel support system of T341 tunnel of Ankara-Sivas High Speed Train Project were completed recently. Throughout the tunnel excavation, serious stability problems occurred both in the entrance portal section and tunnel. The purposes of this study are to explain the failure mechanism and to propose a suitable support system for the section between Km: 341 + 040 - 341 + 114. Tunnel works were interrupted after the collapse, which occurred in a section of approximately 74 m between Km: 341 + 040 - 341 + 114. As a result of the collapse in the tunnel, local settlements emerged on the surface and it was observed that the effects of the collapse on the surface, as well. To surpass the collapsed section, extra reinforcements were performed by grouting taking place both at the surface and inside the tunnel. Afterwards, tunnel excavation was completed in relatively short stages by applying double umbrella system and rigid support system. Consequently, the causes of the failure, excavation and support system design and results of the numerical analyses are discussed.
Evaluation of collapse mechanism and portal interaction of a High-Speed Railway Tunnel (T29 Tunnel, Turkey)
Authors: Aygar E B , Gokceoglu C
Published: September 2021

Within the scope of the Ankara-Istanbul High Speed Train Project, the T29 tunnel was opened to traffic after completing excavation and support implementation. The tunnel was excavated in weak to very weak graphitic schists causing severe face stability problems and deformations on the tunnel supports during excavation stage. In the progress of the excavation stage, a serious face failure occurred at Km: 225 + 784, and the effects of this face failure were observed on the surface. Since the cover thickness is approximately 35 m in this section of the tunnel, it was decided to pass this zone with a cut and cover structure. The portal excavation was carried out from the failure zone, and it was planned to provide stability with the closure of the surface by constructing a cut-and-cover structure immediately afterwards. However, slope failures occurred during the portal excavations. This section was reworked, and it was decided to support this area with a pile system. Consequently, in this study, the reasons for the face failure and slope failures are investigated, and the construction stages are explained and discussed.
Sensitivity analysis of a new model to predict the survival probability of artificial rock blocks upon dynamic impact
Authors: Guccione D E , Buzzi O , Thoeni K , Fityus S , Butcher C , Giacomini A
Published: September 2021

Rockfall fragmentation is a very complex phenomenon that is still poorly understood and modelled. Being able to adequately model fragmentation of impacting blocks, including change of shape, size, and energy after breakage, is essential to be able to predict realistic trajectories and design effective mitigation measures. In order to develop an accurate predictive model for rockfall fragmentation, it is necessary to better understand the fragmentation process and its likely outcomes. A novel model was recently proposed by the authors which can predict the survival probability (SP) of brittle spheres upon impact from the statistical distribution of material parameters, obtained by standard quasi-static tests (Brazilian tests and unconfined compression tests). The survival probability is described as a Weibull function whose two parameters (shape parameter-m-and scale parameter - critical kinetic energy) are predicted by the model. The model is based on theoretically-derived (from Hertzian contact theory) conversion factors used to transform the critical work required to fail disc samples in quasi-static indirect tension into the critical kinetic energy to cause failure of spheres at impact in vertical drop tests. This paper presents a sensitivity analysis on the parameters which influence the prediction of the critical kinetic energy.
Rock joint scale effects in numerical modelling - Hinkley Point C, a case study
Authors: Ogunmakin B A , Koe A , Jean-Philippe M
Published: September 2021

This paper presents the details of the approach to numerical modelling of the subvertical rock slopes resulting from the deep excavations associated with the foundations and basements for Hinkley Point C, Nuclear Power Station, in Somerset, UK. The ground model, which was based on an extensive ground investigation, indicated that the rock mass comprised thinly bedded mudstones and occasional limestones of the Blue Lias Formation. The structural geology of the site consisted of two major faults with five minor faults. These faulting resulted in highly fractured rocks with closely spaced discontinuities with unfavourable orientations and dip angles relative to the slope face. The design methodology for the project included Discrete Element Method (DEM) of numerical modelling using UDEC, a commercial software suitable for modelling fractured rock behaviour. As part of the development of the analytical model, a number of simplifications in terms of modelling, needed to be undertaken to enable development of a series of models that adequately reflected the likely ground conditions during excavation, but that could be run effectively under the usual constraints of a commercial project. One of such key simplifications relates to rock joint spacings. Modelling the rock joints spacings as measured on site in UDEC would result in extremely long computation time. It was necessary to scale up joint spacing in the model without compromising on the accuracy of the results. Series of sensitivity analyses were carried out to assess the effects of joint spacing on the slope stability analysis. From these analyses, an appropriate joint spacing scale up factor was derived. The output from the modelling included assessments of likely displacement of the rock slopes during excavation and as part of the construction works for the basements a programme of extensive monitoring was undertaken to verify the results of the modelling. The paper presents the ground model as interpreted from the ground investigation, the sensitivity analysis undertaken to help develop the approach for the analytical model and the results of the numerical modelling. It then goes on to compare these with the actual ground conditions revealed as excavation was undertaken, and the deformation recorded on the rock slopes during excavation. The paper goes on to present conclusions with respect to the modelling similar rock masses effectively using numerical modelling techniques.
Finite element for Richards’ equation in porous rocks
Authors: Scussiato T , Ferrer A M , Ito W H , de Queiroz P I B
Published: September 2021

The interaction processes of water movement and environment have several aspects important to engineering and geology, which motivate a large amount of research all over the world. As computers with larger capacity become available and affordable, several simplifications used in the past have become meaningless, and nonlinear complex phenomena like unsaturated flow can be processed in affordable machines. The reduction of water flow capacity of filters and drains in embankments due to unsaturated zones, and the environmental problems of remediation of contaminated zones in porous rock masses at the vadose zone are examples of special problems in which advanced modeling should be applied to avoid misleading conclusions or dreadful consequences. The unsaturated flux can also be important in understanding the influence of humidity in the bowing phenomenon in calcitic marbles, since laboratory tests have shown different evolutions of this pathology in partially saturated samples and in completely wet or dry samples. Moreover, this formulation also has important application in building envelope modeling, like in evaporative roofs which enhance thermal comfort in hot weather. To increase the understanding of unsaturated problems, this paper presents a finite element formulation for applications in unsaturated flow in stiff porous media, like sedimentary rocks or concrete. The formulation is based on Richards’ equation for one-dimensional flows and it includes a linear interpolation of suction, as well as an arbitrary implicit parameter.
High stress gradient, critical factor affecting rock burst in the United States mines
Authors: Maleki H
Published: September 2021

To enhance the understanding of seismicity and violent failure mechanics for development of control measures, significant research has been dedicated in South Africa, Europe, USA, China and Australia within the last century. Considering complexity of coal pillar mechanics, the author has used two approaches for enhancing understanding of violent failure in US mines (1) carefully reviewing field measurements from US mines and (2) applying a hybrid statistical-analytical method for identifying critical factors contributing to violent failure of coal measure rocks. These studies reinforce the significance of higher risks where mining in areas of high stress gradients, increasing the potential for sudden failure of near seam strata, depending on geologic and stress conditions. High stress gradient condition is commonly found while mining adjacent to some geologic structures (faults/grabens), multiple seam solid-gob crossings and even occasionally on development where failure of highly stressed roof/floor units triggers seismicity and the failure of marginally stable pillar ribs. The latter mechanism has also been experienced in hard rock mines and shown to be associated with buckling failure. Example of stress conditions from case studies are analyzed in this paper.
Research and assessment of the rock burst hazardous of the Kola Peninsula mineral deposits by seismic-acoustic monitoring data
Authors: Rasskazov M , Rasskazov I , Gladyr A , Tereshkin A , Tsoi D , Rasskazova A
Published: September 2021

The results of geomechanical studies to assess the rock burst hazard at the deposits (Kukisvumchorr and Apatite Circus) of the Kola Peninsula are presented in the article. These results are obtained by special set of technical means, including an automated seismic acoustic rock pressure monitoring system “Prognoz-ADS” and a portable geoacoustic device “Prognoz L” developed at the Mining Institute of the Far Eastern Branch of the Russian Academy of Sciences. Based on the measurement and analysis of the parameters of seismoacoustic events, reflecting the geomechanical processes in the mined rock mass, maps of seismoacoustic activity combined with 3D mining and geological models of mines were developed. Based on the analysis of the spectral parameters of the signals, it was concluded that the use of the developed software and hardware complex is promising for predicting dynamic phenomena in the rock massif. The rock burst hazard can be assessed by the measuring complexes at these deposits; necessary safety measures can be taken for decrease of geodynamic risk.
Experimental investigation of double scroll cutting pattern by using button cutting tool of raise boring machines
Authors: Copur H , Shaterpour-Mamaghani A , Gumus A , Tumac D , Balci C , Kocbay A , Erdogan T , Avunduk E
Published: September 2021

Full-scale linear cutting test is one the most preferred and reliable methods for performance prediction of mechanical miners. Raise Boring Machines (RBMs) are one of these mechanical miners which are commonly used for drilling / excavation of shafts for different purposes in mining and tunneling projects. This study aims at investigating experimentally double spiral (scroll) cutting pattern in raise boring machine. Full-scale linear cutting tests are performed by using button (kerf) cutting tool. The tests are performed at line spacing of 25 mm and varying depths of cut per revolution by using two hard rocks (diabase and granodiorite) that were obtained from the Yusufeli Dam and HEPP project site. The average and maximum normal, rolling and side forces; specific energy; yield; and coarseness index are measured in each cut. The study indicates that optimum ratio of line spacing to depth of cut per revolution are obtained as 8.3 and 4.2 for diabase and granodiorite samples, respectively.
Failure Analysis of an Intersection under Squeezing Rock Conditions
Authors: Ozturk H , Foo B
Published: September 2021

The development of Turkey’s deepest coal mine is currently underway to the proposed depth of 1200 meters (m) below surface at the Soma Coal Basin. An 11 m intersection forming an access way from one of the main declines was excavated at approximately 900 m below surface collapse within hours of completion even after being heavily supported by TH34 and cable bolts. It was discovered during the excavation failure investigation and rehabilitation work that the intersection was excavated below a water bearing stratification and faulted zone of the coal seam. The failure analyses concluded that the failure was contributed by a number of factors, mainly the overburden pressure of the overlying material along with the inrush of high-pressured groundwater with the very poor rock mass surrounding the excavation. This study investigates the possible reasons of the failure, numerical modelling of the intersection and alternative support suggestions for such squeezing rock conditions.
Experimental study of ore lifting efficiency with mixture of bentonite suspension and sand as a carrier material for deep sea mining
Authors: Orita K , Tani K , Suzuki A , Kosho T
Published: September 2021

Carrier material (mixture of viscous fluid and fine particles, CM) circulation system was proposed to lift up deep sea mineral resources. This study focuses on appropriate mixing proportions of CM for lifting up heavier and coarser ores. The results of model tests of ore lifting demonstrated that CMs of mixture of water, bentonite and sand particles could lift up heavier and coarser ores than those lifted in the conventional system by far lower vertical flow velocities. Moreover, ore lifting efficiencies were found to be improved by restricting movements of CMs around ores via the wall of the vertical pipe.
An approach to estimate coal pillar strength
Authors: Sharipov A S , Adoko A C
Published: September 2021

In this paper, a probabilistic design chart for coal pillar based on South African coal mine experience is proposed as a tool capable of estimating the pillar strength. A methodology based on the logistic regression is employed to identify failed and intact pillars with their corresponding probabilities of occurrence. The input parameters used for pillar design include the mine depth, pillar width, bord width, height of mining excavation and panel width. The results showed that 84.6% of the pillars, including stable and failed categories, were correctly classified. In addition, the probability associated with the pillar conditions was determined and plotted in form of a pillar strength graph. The results were in good agreement with the field data and existing studies. One of the merits of the current study is that the probability of having a coal pillar intact or failed can be easily determined. This is particularly useful for design purposes since a series of uncertainties are usually involved in collecting the rock mass parameters. It is concluded that the results of this study could improve the empirical design of coal pillars.
Implications of in-situ stress measurement in mining engineering
Authors: Li Peng , Wu Yunquan , Cai Meifeng
Published: September 2021

Knowledge of the in-situ stress conditions in mining areas is very necessary for scientific mining design and effective disaster control measures. The object of this article is to systematically introduce the in-situ stress measurement method and its implications in mining engineering, including mining design optimization, rockburst mechanism and prediction, stability control of surrounding rock, fault stability assessment, exploration and development of coalbed methane, coal and gas outburst prediction, evaluation of water inrush from coal floor, and high-stress rock breaking. The research results are of great significance to realize the safe, economic, and efficient recovery of mineral resources.