The wear of the bits on a continuous mining machine is a problem that affects mine operators around the world. The fundamental problem (wear) still causes increase in the downtime of the equipment. One aspect, which has been surprisingly overlooked, is the heat developed on the bits during cutting that causes the wear of the bit. Numerical models of the Automated Rock and Coal Cutting Simulator (ARCCS) were developed using the ABAQUS. Two bit designs K-1M and K-2M were analyzed numerically and it was found that the effect of heat developed on the bit not only depends on the friction but also on the bit geometry. Forces developed during the rotary cutting showed that the sharper and the longer bit tips are more effective compared the regular conical bit tips.
Longwall and room-and-pillar methods of mining are the most popular method of extraction of the coal in the United States. These methods use versatile continuous mining machines such as the continuous miners and the shearers for the development and the production from the mine. Bits mounted on the continuous miner and shearer drums are the primary elements that are responsible for coal extraction. Additionally, both the continuous miner and the shearer are affected severely due to wear of bits.
Prominently the worn bits will result in:
1. The downtime of the continuous miner.
2. An inefficient cutting of coal.
3. An increase in dust near the work area.
4. Frictional spark and ignition of gas.
5. An overall economy of the operator.
In deep tunnels the knowledge of in-situ rock temperatures is of great importance, e.g. for the design of ventilation and cooling. A finite element model simulation technique for rock temperature prediction is described. The method handles complex thermal/hydraulic characteristics, pronounced topographic relief, deep groundwater circulation, transient coupled heat/fluid transfer, uplift/erosion and thermal history. During tunnel excavation the rock temperatures were measured. The procedure has been verified by comparing measurement and prediction under Alpine conditions, namely in the Gotthard base tunnel, Switzerland and the Koralm Tunnel, Austria: The agreement is well, within ±15%. Reliable simulations call for a solid data base; e.g. surface temperatures, basal heat flow and uplift/erosion patterns must be determined beforehand. The range of geothermal and hydrogeologic properties should be known. Only temperature data along the planned tunnel trace below the highest cover, preferably measured in well positioned boreholes, enable proper model calibration.
The distribution of in-situ rock temperatures in deep tunnelling is of predominant importance in planning, construction and operation, e.g. for the design of ventilation and cooling. The determination of rock temperatures along a planned tunnel trace at depth is especially a demanding task in mountainous terrain. The rock temperature field within a mountain massif is the result of heat transport processes (heat conduction and advection) and depends on several boundary conditions (e.g. surface temperature, basal heat flow) as well as on numerous parameters (e.g. 3-D topography, distribution of geological units/of thermal conductivity, water circulation pattern/distribution of hydraulic conductivity), along with transient processes like uplift/erosion or paleoclimatic changes. The complexity of these parameters calls for a correspondingly flexible and efficient calculation method. Only advanced numerical model simulation can cope with these manifold requirements. The development and application of such a modelling approach is presented for the Gotthard Base Tunnel (GBT), Switzerland, combined with its verification based on actual measurements along the excavated tunnel.
The City Rail Loop project is a planned urban railway line for commuter trains under the Helsinki city-centre. The triple tunnels run under the very densely-built city-center peninsula. Three underground stations will be built along the new looped railway. The central downtown station will be constructed under extensive existing underground infrastructure. There are several parking caverns, service and sewage tunnels and an existing metro station in the immediate vicinity of the planned underground downtown railway station. The station will be connected directly into several existing underground facilities including the adjacent metro station. During the construction these existing facilities should be able to operate normally. In addition, major brittle fault zones intersect the planned station. These pose interesting challenges in the project that are dealt with through rock mechanical analysis. The rock mechanical models were used to guide, and advise the engineering design and layout planning of the station caverns.
1 Introduction and Background
The City Rail Loop project, (named ‘Pisara’), is a planned urban railway line for commuter trains under the Helsinki city-centre (Figure 1). The railway is roughly 8 kilometers in length, and is a loop-shaped (Pisara = ‘droplet’ in Finnish). The plan calls for two rail tunnels and an adjoining service tunnel that runs parallel to the rail tunnels. In total, roughly 25 kilometers of drill and blast tunnels will be excavated. This triple tunnel system runs under the very densely-built city-centre peninsula, which is surrounded by the Baltic Sea on three sides. The tunnel will pass under the sea at a narrow strait on the city’s east side. The detailed planning of the railway line is scheduled for 2013-2016.
Three stations will be built along the new looped railway. The downtown station (connects to the Central Railway Station) will be constructed under the extensive existing underground infrastructure. There are several parking caverns, service and sewage tunnels and an existing metro station in the immediate vicinity of the planned underground downtown Pisara railway station. The station will be connected directly into several existing underground facilities like the adjacent metro station cavern. During the construction these existing facilities should be able to operate normally.
The complex station design and the close proximity to, and interconnection with existing underground and above ground spaces pose interesting challenges with respect to the rock mechanics and the engineering design. This paper presents and discusses the rock mechanical analyses that was done to guide, advise and support the engineering design and layout planning of the downtown station caverns and the related access tunnels.
The assessment of abrasiveness and hardness of rocks have been extensively covered by previous researchers, with little attention to flints, which were only described as highly abrasive. However, analysis of flints has shown that abrasivity of flints varies. These parameters are important inputs for the prediction of drill bit wear rate and design of various parts of drilling/tunneling/mining equipment. In this paper, a classification of flints (sampled from the English, French and Danish Chalk) which correlates with the abrasivity and hardness of flints is proposed. The results showed lighter/grey flints (with more calcite) have lower potential to cause drill bit wear as indicated by hardness and geotechnical wear indices than dark flints. This tends to suggest that even small variations in the carbonate content results in significant variation in abrasivity and that colour can be used as an indication of the potential of flints to cause tool wear.
In most continents, flints are found either as nodules, sheets or as extensive thick beds (tabular) in chalk. Encountering flints during engineering works usually leads to challenges affecting the entire project execution/costs. These threats are among the major factors affecting engineering projects in chalk. The problems are in the form of abrasive wear of drilling/tunneling tools, which are mostly felt during excavation because they were not envisaged at the preliminary stage of the project. This usually leads to costly changes or redesign of both the project or excavation machinery and associated cutting parts (Hahn 1999, Mortimore 2012 and Varley 1990). Therefore, proper understanding of wear properties of flints will help in predicting their potential to cause drill tool wear, and will also aid in the design of excavation systems before onward mobilisation to the field.
Unfortunately, despite the persistent threats posed by flints, the hardness and abrasiveness of flints are not well understood and attempts to understand these are very limited. Similarly, to date, no attempt has been made to relate the hardness and abrasiveness of flints to their various colours. Thus, this paper looks at the wear properties of flints using Shore Hardness (SH, n= 39), Cerchar Abrasivity Index (CAI, n= 71), X-Ray Diffraction (XRD, n= 14), Vickers Hardness Number of Rock (VHNR, n=14), Rock Abrasivity Index (RAI, n= 108), Scanning Electron Microscopy and Image analysis (ImageJ). These methods were used to determine the abrasive properties of flints and to define which flint has more chance of causing drill wear, when characterized by colour. The aim is to establish a simple classification of flints for prediction of tool wear rate based on colour variation, for use at the preliminary phase of site investigations.
Selection of support system is important for safety concerns and economic aspects. The purpose of this study is to investigate the design of support system specific to an underground mine in Balya, Balikesir, Turkey. The mine has been operated by Eczacibasi Group Esan Company since 2009 for lead and zinc production. Support systems were designed by using rock mass classification systems based on the data regarding underground openings, rock mass and support materials. The suitability of the designs were evaluated by using numerical methods to understand the effect of support materials by considering the difference between total displacement and strength factor both for supported and unsupported conditions. The effect of existing underground openings that are adjacent galleries were also simulated in the numerical models that could not be modelled in rock mass classification systems. The studies were completed a design procedure for a similar underground mines successfully.
Design of support systems is an important part of planning as well as site applications for a sustainable ore production. The studies are mostly carried out by considering in situ stress, stress around the openings, evaluation of rock burst, and squeezing conditions. Rock Mass Rating (RMR) proposed by Bieniawski (1989) and Q-system (Barton et al. 1974) classifications are employed as empirical methods to select support systems for underground openings. The results obtained from these studies can be combined to design underground opening’s support system. These empirical methods similar with the analytical solutions mostly ignore the effect of existing underground openings. In order to obtain proper and optimized solutions during support design studies, some other methods such as numerical methods should be applied to understand the effect of other important features around underground openings. Underground mining with its complicated underground structures requires different solutions for support design problems due to its complicated and intricate structural relations based on underground mine production method.
A lead and zinc underground mine is selected as a case study area that is operated by Eczacibasi Group Esan Company since 2009. The mine is located in Balya Balikesir, Turkey (Figure 1). A mineral processing plant with a daily capacity of 4,250 ton raw ore material has been also operating as a part of the mine. Production of the underground mine is sternly 4,250 ton per day, and the mine reaches 745 m depth for present. The mine is one of the important underground metalliferous mine in terms of its capacity, depth, and daily production rate in Turkey. Sublevel cut and fill stoping underground mining method has been applied for the production of ore. The ore is produced from sublevel production galleries where levels are constructed in every 15 m height. The open stopes are filled by cemented backfill material for the excavation of adjacent production galleries as well as forming working platforms for upper sublevel. The size of the production galleries are in rectangular shape with 25 m2 area while the size increases up to 36 m2 area since the mine goes down deeper. Fibrecrete, rock bolts, and wire mesh are the main support materials and engineering properties of these materials were also determined in order to simulate the suitability of support materials for underground openings.
Bock, Barbara (Ruhr-University Bochum) | Alber, Michael (Ruhr-University Bochum) | Rogall, Michael (Geological Survey and Mining Authority of Rhineland-Palatinate) | Wehinger, Ansgar (Geological Survey and Mining Authority of Rhineland-Palatinate) | Scherschel, Jürgen (Baugrundinstitut Franke-Meißner und Partner GmbH) | Sachtleben, Volker (Baugrundinstitut Franke-Meißner und Partner GmbH)
As a relict of former subsurface basalt mining activity within the municipal area of the city of Mendig (Germany) an area of about 200,000 m² of disused pillar supported mining openings still exists at about 15-20 m below the current ground surface. After the shutdown of mining, numerous pillars experienced brittle deformation and several surface collapses occurred. To prevent any further harmful damages, a risk assessment with modeling of relevant parts of the mining openings is carried out currently. The geomechanical input data for modeling are based on the results of numerous laboratory tests. The test results indicate that pillar failure is strongly influenced by a combination of particular pillar properties like geomechanical properties as well as geometric pillar properties.
In the course of the 19th and 20th century extensive subsurface mining activities for the exploitation of the well-known “Mendig basalt” have left behind exhausted stope-and-pillar mining plants below the city of Mendig, Germany. During the mining activities, the remaining pillars had to ensure the support of the overburden and to provide a stable and safe surface environment.
For some of the basalt pillars below the meanwhile intensely developed urban areas of Mendig, the uniaxial compression strength (UCS) has been exceeded later on and consequently the corresponding pillars experienced brittle deformation after the shutdown of the mining plants.
In order to assess the currently given rock mass strength of the remaining pillars, the mechanical properties of the pillars (e.g. uniaxial rock and rock mass strength) as well as the geometrical properties of the pillars (e.g. cross sectional area, height, shape, axial orientation and slenderness) have to be considered.
The compilation and interpretation of a corresponding data base is the topic of a current research project. The project includes desk studies and site investigation drillings for the exploration of further suspected subsurface mining areas, 3D laser scanning and geotechnical mapping of known and explored mining areas, as well as core sampling, the execution of laboratory tests, and the numerical modeling for the stability assessment of known mining areas.
The long-term deformation behavior of the Callovo-Oxfordian and Opalinus clay rocks has been extensively investigated with laboratory experiments under various thermo-hydro-mechanical conditions. For the highly consolidated clay rocks, the effective stress is both theoretically and experimentally examined by involving the bound porewater between clay particles. The long-term deformation of the clay rocks is determined with triaxial creep tests on water-saturated samples at ambient temperature. Reponses of the clay rocks to humidity changes are examined by drying and wetting the samples under different load conditions. Thermal effects are studied by heating and cooling the stressed samples in drained and undrained conditions. Major findings are presented and discussed in this paper.
Clay formations are being globally investigated as host medium for deep disposal of high-level radioactive waste. The long-term deformation behavior of the clay host rock under varying repository conditions is crucial for the long-term performance and safety of a repository. This key issue has been extensively studied by GRS for the last decade with laboratory experiments on the Callovo-Oxfordian and Opalinus claystones (Zhang et al. 2004, 2007, 2010, 2013). Relevant thermo-hydro-mechanical conditions expected in the potential repositories were simulated in the experiments: (1) stress ranging from the initial lithostatic state to redistribution after excavation, (2) humidity variations during the excavation ventilation and water migration from the farfield to the nearfield, and (3) heating from ambient temperature to the designed maximum of 900C and subsequently cooling down again. Most tests lasted over long time durations up to several years. Major findings are summarized in this paper.
2 Characteristics of Claystones
Core samples were taken from the Callovo-Oxfordian argillite (COX) at the Meuse/Haute-Marne- URL in France and the Opalinus clay (OPA) at the Mont-Terri-URL in Switzerland. Both argillaceous formations are results of a specific geological history that lasted hundreds of millions of years, beginning with deposition and aggregation of fine-grained particles in sea water, followed by sedimentation and consolidation with a concurrent expelling of porewater, development of diagenetic bonds between mineral particles, and other processes. They have been highly consolidated to low porosities of 14-18%. The pore sizes mainly range from nanoscale in between the parallel platelets of the clay particles to micro- and mesoscale between solid particles. The fraction of pores smaller than 20 nm amounts to about 60-80% for the clay rocks (Bock et al. 2010). On average, the COX claystone contains 25-55% clay minerals, 20-38% carbonates and 20-30% quartz, while the OPA clay-schist has higher clay contents of 58-76%, less carbonates of 6-24% and quartz of 5-28%. The clayey matrix of the clay rocks is embedding other mineral particles. The clayey matrix consists of particles with strongly adsorbed interlayer water and strongly to weakly adsorbed water at the external surfaces. Water in large pores is freely movable.
Currently there is no uniform and consistent documentation of unexpected standstills available, which can be applied during the excavation of tunnels with tunnel boring machines (TBM). Such a documentation and evaluation would be helpful for the estimation of risks, costs and the advance rate for future tunnels excavated with a TBM. An approach for a documentation of unexpected standstills of hard rock tunnel boring machines, such as open gripper TBM, single shield TBM and double shield TBM, was developed at Graz University of Technology. This paper shows the results as well as the benefits of a detailed and continuous event documentation during tunnel excavation. The new approach can be taken as a basis for future documentation of unexpected standstills in TBM tunnelling.
Nowadays large infrastructure projects with long tunnels, such as the Semmering base tunnel or the Brenner base tunnel in Austria, are in planning state or under construction. The length of such tunnels as well as the advantage of a fast excavation in favourable rock mass conditions make the use of a tunnel boring machine more and more important.. As for conventionally excavated tunnels, an excavation with a tunnel boring machine demands a detailed estimation of costs, risks, advance rates and construction time in advance, too. Boundary conditions have to be identified as exactly as possible in order to choose the most suitable machine type. Therefore, a detailed and continuous documentation of unexpected standstills of the tunnel boring machine applied during excavation would provide a proper basis for the design of future TBM driven tunnels. The documentation needs to be done contemporary. Reasons for standstills must be evaluated and interpreted. In addition to the documentation of the standstill reason, implemented measures to resume excavation again, have to be documented. Figure 1 shows a flow chart of such a documentation and the use of gained experience for future projects.
Rockfalls are very common along the Himalayan roadways because of the highly jointed nature of rock mass. Discontinuities in the rock mass render them extremely anisotropic, reduces the strength and create avenues for different failure mechanisms like planar, wedge and toppling in destabilizing the slopes. The formation of overhangs due to excavation, coupled with the high density of joints make them a highly susceptible zone for the initiation of rockfall activity. The present study area is a part of seismically active Himalayas (Luhri, Himachal Pradesh), where the occurrence of mild to major tremors are quite rampant. Thus, the study concentrates on the possibility of initiation of rockfall activities due to seismic activities using distinct element modelling (DEM) approach. The results shows contrasting difference in the magnitudes between displacement and velocity in static as well as in dynamic case, causing rockfall to initiate in the latter case.
Rockfall is a major concern along transportation corridors in hilly areas, usually prevalent in the jointed rock slopes (Ferlisi et al. 2012 and Budetta 2004). It is a two-stage phenomenon where initial stage is the detachment of blocks while the second stage relates to the motion of the falling body, post failure. The main triggering factors for the detachment of blocks are erosion and weathering along the structural discontinuities, rainfall, earthquakes and others (Dorren 2003, Singh et al. 2010, Asteriou et al. 2012). Studies have shown a good correlation between the landslides density and the areas of strongest ground motion, while their frequency declines on moving away from the epicenter (Meunier et al. 2007). Sepulveda et al. (2005) studied the rock slope failure due to topographic amplification of strong ground motion in case of Pacoima Canyon, California and observed that the most frequent failure was planar and wedge type derived from rockfalls in many cases. The dominant mode of failure can be established from the relationship between the orientation of structural discontinuities and surface topography at any particular site, but the analysis of mechanism behind the initiation of rockfall due to seismic shaking requires the application of rigorous numerical models that have the capability to model large strain of a discontinuous media. Seismically induced rockfall occurs as a combined effect of gravity and seismic acceleration producing short-lived stress, which exceeds the cohesive and frictional strength of the earth materials (Newmark 1965). As a result, slope failure can take place due to slight disturbance in slopes that may have been stable under static loading time. Earthquakes produce two types of ground accelerations. Out of the vertical and horizontal accelerations, the later one is known to cause greater impact on slopes (Romeo 2000). Past studies have shown that even an earthquake of magnitude 4.0 can trigger a rockfall activity (Keefer 1984). The threshold displacement responsible for causing landslides ranges from 2-5 cm (Wilson & Keefer 1985).
This paper presents a grain-based discrete element model for simulating the quasi-brittle failure of rocks and associated permeability evolution under hydro-mechanical loading. In this approach, the development of crack along grain boundaries controls the degree of damage and the associated permeability alteration in material. As a result, the overall permeability of the model, which is a function of degree of micro-cracking and crack connectivity, can be calculated at each stress state. Micro-mechanical parameters of the model is calibrated to Lac du Bonnet granite such that the model reproduces the physics similar to that of the rock during compression and tension. The numerical experimentations demonstrate the capability of DEM-Voronoi model to mimic the pre- and post-failure response of materials. The calibrated model accurately predicts, in a quantitative sense, the macroscopic properties of granite such as elastic properties, damage thresholds, peak strengths, triaxial strength envelope, and hydraulic conductivity of granite at critical damage thresholds.
It is well-documented in geomechanics-related literature that the permeability of the rock is highly stress-dependent (e.g. Souley et al. 2001). This stress-dependency is due to the fact that when rock is subjected to mechanical loading, the rock microstructure can close, open, extend and induce new cracks, which in turn change the mechanical and hydraulic properties of rock. As a result, the stress-dependent permeability is a function of two fundamental mechanisms: (i) microcracking-induced permeability change which is related to growth of the micro-cracks, and (ii) stress-induced pore volume change in which the pore volume is a function of interaction between fluid pressure and mechanical stress. In the former case, damage-modified permeability evolution relates to heterogeneous nature of rock material and presence of internal micro-structure with different sizes and properties. Thus, when the rock is subjected to a compressive load, local tensile stress concentration induced on these internal micro-structures initiates a complex process of fracture propagation in rock. Generation of these crack corridors (channels) modifies the overall permeability of the rock by the extent that is dependent on the opening, density, connectivity of such cracks.