ABSTRACT In recent years, numerical simulations have been used widely for investigation of mechanical rock cutting. However, the capability of the modelling methods has yet remained open for question. In an attempt to address the shortcomings of the existing methods, this paper proposes a new extension of combined finite/discrete element method (FEM/DEM), which takes into account the mix-mode I-II fracture criteria for predicting the initiation and propagation of cracks. The code's ability in modelling rock fracture process is investigated by simulating fragmentation with a mechanical cutter. The model characterized the rock-tool interaction, computing the direction of crack growth leading to chip generation. The obtained results demonstrated the capability of the proposed combined FEM/DEM method in modelling mechanical rock cutting process. The code could successfully handle the chipping process, being able to model the stress concentration, crack initiation, crack propagation and chip separation. 1. INTRODUCTION During the past decades the application of mechanical tools for rock fragmentation has been extended widely in mining and civil engineering industries; providing a more flexible and environmentally friendly alternative to conventional blasting method. However, the rock fragmentation mechanism with a mechanical cutter has not well understood due to the complexity of the dynamic interaction between mechanical tool and rock, and rock fracture process (Ghamgosar and Erarslan, 2015). While rock cutting experiments are largely used to investigate the cutting process and the associated cutting forces, the extensive number of variables and effective factors influencing the process have made the application of these tests relatively limited. The developed analytical and empirical methods also suffer from same drawback. The recent advancements in numerical modelling methods have confirmed to provide robust tools for simulation of complex problems. Hence, different numerical techniques have been considered for investigation of rock fracture process. The rock cutting process comprises of four stages that should be addressed in a numerical simulation; generation of crushed zone under the tool, cracks initiation and propagation from crushed zone, cracks coalescence and chipping process chip separation. Not all of the numerical techniques are able to model the entire rock cutting process.

ABSTRACT Undoubtedly, Roadheaders are one of the most versatile excavation machine types operated in soft and medium strength rock formation's tunneling and mining. An essential aspect of a successful roadheader application is definitely the performance prediction which is basically concerned with machine selection, production rate and also bit consumption. Evolving a new roadheader's performance prediction model in various operational conditions and also different material is the primary intention of this research. Investigation on previous works revealed that three main features have great influences on the bit wear of a roadheader. Brittleness which can be utilized as a cuttability factor in mechanical excavation perspective is actually one of some parameters which is absolutely in relation with breakage properties. In addition to the rock brittleness, rock quality designation (RQD) and instantaneous cutting rate are employed as input parameters for the prediction of pick (bit) consumption rate (PCR). For the purpose of this paper, using previously published field datasets, a new prediction model using the application of artificial neural networks as an artificial intelligence technique is developed, trained and tested to estimate PCR based on data of brittleness, RQD and instantaneous cutter rate. Results demonstrated that PCR is highly correlated to the input parameters, and the ANN model could produce acceptable predictions. INTRODUCTION In recent years, mining business has been under the influences of global trends, environmental limitations, and variant market requirements to be more and more productive and profitable. Utilizing mechanical miners like roadheaders, continuous miners, impact hammers and tunnel boring machines for ore extraction and excavation of development drivages, increases profitability. The mentioned miners result in continuous operations and consequently, the mechanization of mines with mechanical miners is presumed to make mining projects more productive, more competitive, and less costly. As a result, ordinary drill and blast technique could be avoided. Roadheaders which are applicable in tunnelling, mine development, and mine production of rock types of soft to medium strength, are very adaptable excavation facilities. The efficiency of roadheader application is rudimentary related to machine selection, production rate and bit consumption (Ebrahimabadi et al., 2011).

ABSTRACT The expansion of Lippulaiva is a construction project located in Espoonlahti, Espoo. Existing Lippulaiva shopping center will be demolished and the land area will be excavated simultaneously with the extension of Helsinki metro line – west metro. Espoonlahti metro station will be connected to the new shopping center with two shafts and the station hall is located below the shopping center with minimum seven meters of rock overburden. In September 2017 excavation and reinforcement of the metro station are ongoing. The surface excavation on top of metro station hall starts after demolition of the existing shopping center. Locating two major excavation and construction projects in the same small land property simultaneously requires a lot of cooperation and good will from engaged parties. Several construction concepts were studied and negotiated to integrate the visions and goals of both parties. Rock mechanical simulations were used to identify viable concepts for future development and discard the ones that either were technically too risky or did not produce sufficient value for the investment involved. Characteristic to the areal geology is igneous granite with very little cleavage and amphibolite with some cleavage. The rock mass is mainly jointed non-systematically. The geological conditions at the site play a major role in the design process as the area encompasses several weakness zones, some of which pass through critical sections of the excavations, such as the shaft openings. These geological features have dictated some design choices during the property development as some excavation combinations were not considered feasible after detailed investigations and rock mechanical simulations. Most of west metro tunnels will be excavated and reinforced prior to the excavations of the shopping center. This means that significant measures are taken to ensure that the shopping center excavations or foundation loads do not damage the existing underground spaces of the metro line or the installed reinforcement structures. To increase the challenge, the in situ- stress measurements done at the site were inconclusive – there is a big variation in the results of the major horizontal stress component magnitude at the metro station level varying from 1-12 MPa. Also, the orientation of the stress field is unclear. This uncertainty was mitigated by running several rock mechanical simulations with varying stress fields to find out the best and worst case scenarios.

ABSTRACT After the multistage hydraulic fracturing operations, it is generally observed that the shale gas well is characterized by low flowback rate and high-salinity flowback water. It can be explained by the high water imbibition and ion diffusion capacity of gas shale that is significantly different from conventional sandstone reservoirs. The research on imbibition and ion diffusion is significant for the understanding of shale formation characterization. A new method to evaluate the mean pore size was developed using the experimental data of water imbibition and ion diffusion in gas-saturated shale. The mathematical model was derived theoretically depending on Darcy's law and continuum equation. The results show that the imbibition and diffusion rate can be calculated by imbibition-diffusion curves, and the ratio of imbibition rate to diffusion rate is related to mean pore size. The value of mean pore size is inferred, which is verified by the mercury injection test. This research is significant for volumetric analysis and chemical analysis after fracturing operations to understand the characteristics of gas shale. INTRODUCTION Shale gas, one of the unconventional natural gas resources, becomes the focus of the world. The economical explorations have been taken in several basins of America, Canada and China. As shale gas formation has the characteristics of low-porosity and low-permeability, the multistage fracturing technology must be taken to realize economical exploration (Vera and Ehlig-Economides, 2014). The field studies of network fracturing illustrate that the flowback efficiency of fracturing fluid is generally low. The flowback efficiency of shale gas wells in America is 20~40%, and that of several shale gas wells in Fuling of China is evenly lower than 5~10% (Zhong, 2011). Many researches explain that this is caused by spontaneous imbibition. High capillary pressure due to micro-nano pores and ultra-low initial water saturation ("super dry") leads to the strong imbibition capacity of shale formation that substantially exceeds conventional sandstone formation. (Lal, 1999). The clay mineral content of shale is high, which will result in strong chemical effects. When shale contacts with water, the water is imbibed into shale under the chemical effects. So, the imbibition mechanism in shale is more complicated than that in conventional sandstone. In particular, the existence of smectitie and illite can greatly enhance the water imbibition rate (Yang et al., 2016).

ABSTRACT Cyclic loading on civil structures can lead to a reduction of strength of the used materials. For the materials concrete and especially steel, there are clear design codes about how to account for the reduction of the material shear strength due to this cyclic loading, which is called fatigue. For the material rock, however, there are no design codes or standards for fatigue, in terms of shear strength reduction. For this reason, a large number of laboratory triaxial tests have been performed, in order to evaluate the fatigue of rocks by comparing the shear strength parameters obtained in cyclic triaxial tests with the static shear strength. Tests have been performed on artificial gypsum, a mixture of sand and cement (mortar) and soft sedimentary limestone. Correlations of the fatigue, for both the number of cycles and the cyclic stress ratio, have been obtained. All triaxial tests were conducted on dry samples (no pore pressure) in the natural state. The range of the confining pressure was between 0 MPa and 0.5 MPa. The frequency was kept low to allow for a precise application of the cyclic load and also accurate readings. The number of applied cycles was from a few cycles up to a few hundred thousand. The imperfections in the artificial gypsum have a significant impact on the results of the (especially cyclic) strength tests. Therefore another man made material was used – a mixture of sand and cement (mortar). As the first static test results were very promising, mortar was used in further tests. The cyclic tests, however, presented a similar, high scatter of results as for artificial gypsum. Due to the complex behaviour of the cohesive materials and high scatter of the results, many tests were required. Two different strategies were used to investigate the fatigue of the cohesive geomaterials: the remaining shear strength curve: after a given number of cycles, a final single load test until failure, measures the remaining shear strength of the sample. the typical S-N curve (Wöhler curves): one counts the number of constant loading cycles until failure. The fatigue of rocks can be seen as a reduction of the cohesion. In this way, the fatigue of a cohesive geomaterial can be described by (a reduction of) the remaining cohesion.

ABSTRACT Due to its geological origin, rock mass properties have an inherent variability which brings an uncertainty that should be considered in engineering modeling. This uncertainty is divided in both aleatory and epistemic. The aleatory uncertainty is usually accounted for by conventional probability techniques. However, this approach has restrictions when limited information on variables is available, which is the case in most rock engineering projects. Besides, probability theory cannot consider the epistemic uncertainty properly. On the other hand, in many rock mechanics problems, especially in mining, there are several sources of information at different stages of the project, which should be properly incorporated into the model to assist the decision-making process. Dempster-Shafer theory provides an alternative to deal with both epistemic and aleatory uncertainty, since it allocates probability mass to sets or intervals (Dempster-Shafer structure). Hence, reliability assessment in terms of intervals can be carried out under limited information. A key aspect of the Dempster- Shafer theory is the possibility of combining several pieces of evidence from different sources, considering even conflicting information. With this framework, this paper explores different combination rules for Dempster- Shafer structures, considering a key block problem in a slope from a sandstone mine located in Cundinamarca, Colombia, where information from different sources has been collected at different stages of the operation for 20 years, on both geomechanical and geometrical properties of rock joints. INTRODUCTION Rock masses are natural materials subjected to a long history of stresses including tectonic load, earthquakes, glaciations, subsidence, tidal effects and gravity. In most cases, these stresses bring fracturing on the rock mass. The presence of fractures highly influences its mechanical response under perturbations. In hard rock masses, the geometry and locations of joints, along with slope geometry, define the kinematically controlled mechanisms of rock failures. Some mechanisms are very simple, like planar or wedge failure, in which one or two joint sets along with the slope face define the geometry of the rock failure. For more general problems, involving three or more joint sets, the block theory (Shi, 1985) arises as a powerful tool to identify potential unstable block for a given excavation geometry. Once defined the potentially unstable block geometry, the next step is to assess its stability. The limit equilibrium (LE) is suitable to calculate the stability of potentially unstable rock wedges. Besides, its formulation is straightforward and has a low computational cost, compared to numerical techniques like Finite Element Method or Discrete Elements.

ABSTRACT Seasonal storage of solar thermal energy is an attractive way to utilise the underground space to increase the share of renewables and tackle the global challenge of climate change. One of the methods to store the solar energy is the borehole thermal energy storage (BTES), where the thermal energy is stored in the rock mass using borehole heat exchangers. This study presents preliminary results of numerical predictions for an in situ experiment of underground thermal energy storage in the research tunnel under Otaniemi campus. The in-situ experiment site consists of two horizontal boreholes of 5 m length drilled into granitic rock. One borehole is equipped with a single U-tube heat exchanger, and the hot water is circulated through it to heat up the rocks, while the second hole is used for temperature measurement of the rock. The in situ experiment set-up is modelled numerically using finite element method to investigate the influencing factors and predict its long-term thermal performance. The three-dimensional problem is solved with the transient heat conduction equations and the temperature distribution in the subsurface is obtained during 21 days of operation. A parametric study is performed to find the optimal operating conditions. The results of the numerical predictions are used for a detailed plan of the experiment. The simulated results will be later compared to the measured values obtained in the experiment. 1. INTRODUCTION The problem of the global climate change requires a considerable effort to reduce the greenhouse gas emissions by increasing the use of renewable sources of energy. The public awareness to use alternative energy sources is growing, and market possibilities are emerging. Besides the solar electricity produced by photovoltaic (PV) solar cells, one of the typical applications of renewable energy is the solar heat, where energy from the sun is used to heat up water and space in buildings. Although the price of PV cells is continuing to drop dramatically every year (Kurtz et al. , 2017), the solar thermal energy is still considered to be simpler to storage for extended time periods. The seasonal storage is of particular importance in high latitudes, as it is the case in Finland, where solar insolation is highest in the summer when the heating demand is low and lowest in winter when the demand is high. In Tackling the Challenges of a Solar Community Concept in High Latitudes, Academy of Finland (AOF) project, the solutions for seasonal heat storage in high latitudes are sought.

Abstract The paper introduces design principles of ground support. The topics include underground loading conditions, the natural pressure arch in the rock mass, design methodologies, determination of the factor of safety and compatibility between support elements. A natural pressure arch is formed in the rock mass in a certain distance behind the tunnel wall. The methodology of ground support in an underground opening is dependent on the size of the failure zone and the boundary depth of the natural pressure arch. In the case of a small failure zone, rockbolts should be long enough to reach the natural pressure arch. In the case of a vast failure zone, an artificial pressure arch could be established in the failure zone with tightly spaced rockbolts and the artificial pressure arch is stabilised with long cables anchored on the natural pressure arch and/or by external support elements like shotcrete liners, girdles, steel arches and shotcrete arches. In addition to the factor of safety, the maximum allowable displacement in the tunnel and the ultimate displacement capacity of support elements should be also taken into account in the design. Finally, the support elements in a ground support system should be compatible in terms of displacement and energy absorption. 1. Introduction Ground support design is associated with the rock mass quality, the in situ stresses and the size and geometry of the underground opening. Knowledge of the in situ loading condition is crucial for the design of ground support. The methodology and design principles of a ground support program are determined by the potential failure mode and failure extent of the rock mass as well as the engineering requirements to the maximum allowable displacement. In this paper, some key parameters for ground support design are presented which include the natural pressure arch, the artificial pressure arch established in the failure zone, support layers, the factor of safety, and the compatibility between support elements.

ABSTRACT With the increase of multi-scale simulation demand, the theory of statistical mesoscopic damage and damage pattern has been widely used to simulate the progressive failure process of brittle rock, which is of great significance to reveal the complex failure mechanism of rock and evaluate the geological risk. In this paper, by using the traditional commercial finite element analysis system Abaqus, the statistical meso-damage theory is introduced to study the failure process of rock under uniaxial compression. The study considers that the elastic modulus, tensile strength and uniaxial compressive strength of mesoscopic elements obey the Weibull distribution, which can be used to characterize the heterogeneity and natural defects of rock. The maximum tensile stress criterion and the modified Mohr-Coulomb criterion are used to determine the tensile failure and shear failure of the mesoscopic elements, respectively. Based on the numerical simulation, it is found that the heterogeneity of the mechanics parameters of rock has a significant influence on the stress field distribution and the macroscopic failure characteristics of rock. Moreover, the damage patterns show that the meso-elements of rock are mainly tensile failure, while the shear failure of the elements is very small. The results indicate that the macroscopic shear band of the rock is mainly caused by the meso-tensile failure of the mesoscopic elements. The equivalent peak strength, elastic modulus and failure mode of the meso-numerical simulations are in good agreement with the physical experimental. The study highlights that it is more reliable and true to understand the failure process of rock by using the theory of statistical mesoscopic damage, and the new algorithm simulator can be used to simulate the trans-scale failure process of rock.

ABSTRACT Twenty in situ rock stress measurements using the LVDT-cell method (Hakala et al., 2012) were performed in Posiva Oy's ONKALO investigation facilities during 2009 - 2014. The measurements cover a depth range of 156 m to 420 m below the ground surface. Most of the measurements were performed in the ventilation shaft and access tunnel, two other locations include the rock mechanics investigation niche at the 345 m level and demonstration tunnels at the 420 m level. The LVDT-cell method was developed as an alternative stress measurement method for hydraulic fracturing and to overcome problems encountered with traditional overcoring methods. The main improvements are the large measurement hole diameter which minimizes the adverse effects of heterogeneity and a mechanical mounting system which eliminated glue related problems such as debonding, drifting and long curing times. The LVDT-cell method has experienced several improvements after the first shaft measurement at level 265 m. The most important improvements are based on the verification tests in well known in situ stress conditions in the Äspö Hard Rock Laboratory in Sweden (Hakala et al. 2013) and the development of the quality ranking system and a method to estimate measurement location related error by means of stress magnitude and orientation (Hakala et al. 2016). Two different in situ stress estimates are provided based on the presented LVDT-stress measurement results: The ONKALO area interpretation based on depth gradients for stress tensor components which can be transformed into principal stress magnitudes and orientations. This interpretation is partly questionable as it ignores the recognised effects of geological features and a possible glacial disturbance above a depth of -300 m. The second interpretation is a stochastic approach to define the deposition depth stress state by providing the mean values, confidence limits and characteristics of distribution.

ABSTRACT The role of rock mechanics in the utilization of underground space is becoming more and more significant as the number of caverns are increasing under the central areas of expanding cities. In these areas rock mechanical aspects have to take into account already in the city planning phase when new underground facilities are introduced in the middle of existing underground infrastructure. Sometimes things can be solved with simple methods, sometimes quite extensive numerical 3D – rock mechanical analysis shall be conducted. However, the amount of data available is dictating the methods which can be used. For numerical analysis there must be enough data about the bedrock and in-situ stresses, among others. It must be kept in mind that the accuracy of the analysis is dependent on the accuracy of the initial data. In any case, rock mechanics should be utilized already in the initial design phases of underground construction. INTRODUCTION Rock mechanics is a relatively young science, but the basic ideas of rock mechanics have already been implicitly known to people living in caves. The basic ideas of the safety of caves are still the same as in the Stone Age. The ground type must be at least in some extent intact without any loose layers to be stable. The stability of the cave is controlled by the shape and dimensions of the cave in the condensed ground conditions. In hard rock conditions the stability of rock blocks is controlled by rock joints. Due to the technological restrictions ancient man-made caves and tunnels have been constructed only into the ground which can be excavated by hand tools without explosives. All large caverns were created by natural processes and during ages their shapes became stable. The development in technology created possibilities to make tunnels for different purposes, but also then the design was based on experience. As the theories of statics and strength of materials developed and were applied in structural and geotechnical engineering also the mechanical behavior of the rock structures could be formulated by analytical equations. Much of this work was carried out in Central Europe where a lot of railway tunnels were constructed sometimes in difficult ground conditions. However, the real breakthrough in rock mechanical analysis was achieved in 1970's – 1980's when the development of computers allowed the use of finite-element or other numerical analysis in stability calculations, first mainframe computers and then desktops and laptops. Increased calculation power of computers, advanced software and extended knowledge on rock structure, properties and in-situ stresses have enabled to make more reliable estimates on the rock mechanical effects caused by intended new projects.

ABSTRACT Mining and chemical industries have investigated Thin Spray-on Liners (TSLs) intensively in the past. Mining suppliers, contractors and universities have been promoting a concept, or better, a vision of so called ‘Thin Support Liners’ (TSLs). It is a wish of the industry that sprayed concrete and mesh could be replaced by these thin liners. All TSLs are meant to be applied in 3–10 mm layers and consist of a certain polymer content. EFNARC (Experts for Specialized Construction and Concrete Systems is an European federation which unites national associations and companies involved in concrete repair, flooring, sprayed concrete and the protection and repair of tunnel and mining constructions) changed the meaning of the abbreviation "TSL" to "Thin Spray-on Liner" in 2008. This definition change included a clear reduction to the expectations regarding TSLs. Even though TSLs give a certain amount of surface support, they act more as sealant. Today the usage is mainly accepted in coal mines in certain countries, even though some applications in kimberlite or shaft sinking have shown success. Now Normet is introducing a new product called TamCrete SSL a ‘Structural Support Liner’ to the tunneling and mining industry. This new product is introduced as a spray applied, rapid curing, non-toxic resin based support liner for mining environments. The paper will cover the basics of TamCrete SSL including key mechanical figures and application methods. The paper will also show field test which indicate its waterproofing characteristics. These tests were first carried out as a part of master's thesis and based on these tests the waterproofing characteristics of a cured product seem to be good. INTRODUCTION For decades the underground construction industry has used shotcrete for rock support in tunnels. However, shotcrete takes time to cure which slows down the excavation process. In addition shotcrete forms cracks during curing and water might funnel into the tunnel through these cracks. Now Normet Oy has brought a new kind of Thin Sprayed Liner on the market. This material is called TamCrete SSL (Structural Support liner).

ABSTRACT A new underground wastewater treatment plant is currently excavated at Blominmäki in the city of Espoo, Finland. The Blominmäki plant will replace the current Suomenoja plant. In addition to the wastewater management of 400,000 residents and making provision for improved wastewater treatment, the new plant will also release valuable seaside land for construction. Almost 1 Mm3 of rock will be excavated. In addition to tunnels and large halls, excavation includes 13 shafts as well as decomposition silos with diameter of 20 m. Parts of the facility will have tunnels crossing each other at different levels. The widest span is 30 m and the maximum height of the halls is 22 m. A large number of investigations and laboratory analysis have been made including core drilling, percussion drillings, seismic surveys, soil investigations and core sample stress analysis. A 3D model of the weakness zones was created and rock mechanics simulations were carried out. Rock engineering design included modelling for a multi-disciplinary 3d model of the project. Several weakness zones in bedrock caused need for pre-excavation rock reinforcement. A systematic grouting program was carried out because of the high hydraulic conductivity of the rock. Rock mechanics monitoring program has been carried out using several online extensometers. INTRODUCTION The process basins and technical areas of a large, modern wastewater treatment plant form a complex tunnel network when excavated and built underground. In addition to large spans, excavated caverns are high and tunnels are located in several floors. In addition, in Blominmäki, the new plant has been excavated in bedrock of varying characteristics and in some places bedrock is disadvantageous for rock construction. The location, position and altitude of the tunnel network are largely determined by external constraints, such as the nearby nature reservation area. So, for example, all the weakness zones could not be avoided. One design target has been a systematic process for reinforcement design which ensures an effective excavation work despite of design changes and variable geological conditions in tunnels. Number of bedrock investigations have been required to provide enough output data for reliable rock mechanical simulation results and to identify the most challenging excavation areas before the excavation tendering phase. The design and implementation of a successful rock mechanical monitoring program are based on reliable investigation and simulation results.

ABSTRACT The City Rail Loop is a significant railway development project planned below the Helsinki city centre, Southern Finland. The loop-shaped two-tunnel track railway line runs from Pasila and back via underground stations at Töölö, Helsinki city centre, Hakaniemi. The total length of the railway line is 8 km of which 6 km is underground. The service and rescue tunnel runs alongside the track tunnels. Planning of the railway is still in progress. A large design challenge of the Töölö section comes from the necessity to bypass the large amount of existing tunnels in the area. A 70 m part of the track is designed with a very thin rock cover. Other parts with a total of about 100 m are designed as concrete tunnels using cut-and-cover excavation, including 70 m in the proximity of the Olympic Stadium. Complex geometry of the Töölö station adds to the challenge. The project is co-financed by the European Union, Trans-European Network (TEN-T) and Connecting Europe Facility. INTRODUCTION The City Rail Loop is a significant railway development project planned below the Helsinki city centre in Southern Finland. The public transport system must be able to accommodate a continuously growing number of passengers. At present there are nearly 1.4 million inhabitants in the Helsinki region. This number is expected to increase by 40,000 this decade and by more than 400,000 during the next few decades. The City Rail Loop will enable efficient railway traffic in a large area. As a result of the new railway section, rail capacity can be freed up on the now too congested stretch between Helsinki and Pasila, allowing trains to run at more frequent intervals. The loop-shaped two-tunnel track railway line runs from Pasila and back via underground stations at Töölö, Helsinki city centre and Hakaniemi. The total length of the railway line is 8 km of which 6 km is underground. The service and rescue tunnel runs alongside the track tunnels. This paper concentrates on the design challenges at the Töölö section of the project (Figure 1). The detail design phase of The City Rail Loop was finished during spring of 2017. The reservation of The City Rail Loop in the city plan is valid for 5 years. It may possible to obtain a construction decision during this period but it is also possible that other projects will be politically prioritized ahead the City Rail Loop.

ABSTRACT Crack initiation and propagation is a three-dimensional process. Most of the analytical solutions (such as PKN and KGD models) and numerical models treat crack propagation as a two-dimensional (2D) process. Yet, there is no experimental study, which can provide a one to one comparison in 2D to validate these kinds of models. The 2D experimental set-up equipped with a high-speed camera provides continuous video record and measurement of fracture path. A Speckle Pattern is applied in order to accurately measure surface deformation with Digital Image Correlation (DIC). A transparent material is used in order to have a direct viewing of fracture growth. The results provide information about the breakdown pressure, fracture growth direction, width and fracture speed. INTRODUCTION Hydraulic fracturing has been used in different applications since 1950. There are still many open questions and uncertainties related to hydraulic fracturing. Observing the fracture geometry in field treatments is almost impossible, except in special tests with extensive seismic monitoring (Abe et al. , 1983; Vinegar et al. , 1992), even in those cases it is believed (de Pater et al. , 1994) the data interpretation needs to be more developed. To better understand the behavior of rock during a hydraulic fracturing treatment, numerous studies have been undertaken and several physical models developed to investigate rock behavior during the injection. Laboratory tests should, therefore, serve as benchmarks for numerical simulations. In this study, an innovative two-dimensional set-up is introduced for conducting hydraulic fracturing on low-strength rock-like materials. 1. BACKGROUND There are three different approaches for simulating crack propagation. Analytical, Numerical and physical models are introduced and related literature are summarized.

ABSTRACT Direct determination of the deformation modulus of rock mass needs sophisticated testing equipment, timeconsuming processes and experienced technical staff. However, this modulus has a crucial importance for all rock engineering project to be constructed on or in a rock mass. For this reason, indirect determination of deformation modulus of rock mass has been attractive subject for rock engineers and engineering geologists. For this reason, during the last two decades, several empirical equations based on statistical analysis and several other soft computing algorithms for indirect determination of deformation modulus of rock masses have been proposed. In the present study, a critical review on these approaches is performed and a summary is given. For the purpose of the study, an extensive literature survey is carried out and the approaches suggested are discussed. INTRODUCTION Depending on the increase in World population, new human needs such as high buildings, transportation and energy also increase. As a result of these needs, new infrastructures such as roads, railroads, tunnels, viaducts, dams, ports etch have been constructed and will be constructed. During the project and construction stages of these infrastructures, the deformation modulus of rock mass is necessary. However, field tests to determine this parameter directly are time consuming, expensive and the reliability of the results of these tests is sometimes questionable (Hoek and Diederichs, 2006). For this reason, indirect determination methods can be preferred if the other rock mass and intact rock properties are known well. Considering this reason, during the last two decades, several researchers have suggested empirical equations based on statistical analysis and soft computing algorithms for indirect determination of deformation modulus of rock masses. The main purpose of the present study discusses the approaches suggested for estimation of deformation modulus of rock masses. The static modulus of deformation is among the parameters that best represent the mechanical behaviour of a rock and of a rock mass, in particular when it comes to underground excavations. The deformation modulus is, therefore, a cornerstone of many geomechanical analyses (Palmstorm and Singh, 2001). The deformation modulus is the most representative parameter describing the pre-failure mechanical behavior of any engineering material (Jiang et al., 2009). However, deformation modulus of a rock mass is affected by various rock mass and intact rock properties as well as environmental conditions.

ABSTRACT The ability to use cutting edge tools, such as numerical modelling, to predict seismically active volumes is a clear goal of today's geomechanical engineers. A knowledge of problem volumes in advance of drifting and production would lead to a safer working environment, where risk mitigating design can be implemented. While specific successful cases exist, a standard approach for numerical stress analysis of seismicity is not currently available in the literature. This paper presents the use of numerical modelling to analyse seismically active volumes of Luossavaara- Kiirunavaara AB's (LKAB) Kiirunavaara Mine, a 4.5 km long, iron orebody extracted using sublevel caving. Crack initiation and slip along pre-existing discontinuities were evaluated using Itasca's FLAC3D software and compared to mine seismicity. Results were used to evaluate expected changes in seismically active volumes with planned production. Hanging-wall seismicity was correlated with the location of plastic failure in the models, as well as differential stress near the production front. Less clear relationships existed between footwall seismicity and model results, however, many orientations of discontinues have the possibility to slip, and therefore may contribute to seismicity. Patterns in orientations of discontinuities that can slip were consistent in the footwall drifts relative to the active production level, regardless of the depth of production evaluated. In general, the models did not indicate any expected changes in seismically active volumes with planned production. 1. INTRODUCTION It is undisputable that an understanding of the phenomena of seismicity in rock masses will improve mine safety. Although prediction of specific seismic events does not seem achievable (e.g. McKinnon, 2006), identification of areas that have a higher risk of seismic activity seems within reach. Numerical stress analysis models are the leading-edge tools to understand rock mass behaviour, and much effort has been put towards the modelling of seismicity (e.g. Diederichs, 2000; Andrieux et al. , 2008; Beck et al. , 2009; Sjöberg et al. , 2011; Ghazvinian et al. , 2014). However, to date, a standardised and accepted strategy to numerically model seismicity that successfully reproduces this behaviour for all cases does not exist.

ABSTRACT A large LPG cavern in bedrock has been constructed in the oil industries area of Porvoo, southern Finland. Excavation works were finished in autumn 2016 and the rest of the construction works were finished by June 2017. The filling of the cavern was started in July 2017. The storage capacity of the cavern is about 163 000 m 3 of liquid petroleum gas. The main cavern is situated about 100 m below the groundwater table. The cavern dimensions are: cross section 600 m 2 , width 22 m, height 30 m and length 275 m. The construction of the cavern was made by using the drilling and blasting method and it was supported by rock bolts and steel fiber shotcrete. Host rock of the cavern is of good quality which favors its large size. Rock conditions are known quite well on basis of the numerous previous cavern projects in the area during the past five decades. Rock quality of the site was controlled with investigation drill holes before starting of the construction. The optimum direction of the cavern was justified using elastic numerical modelling and key block analysis. Rock mass water conductivity around the cavern was found to be very low, even one magnitude lower than was expected on basis of the Lugeon tests made in the investigation drill holes. Sustaining of the water pressure around the cavern during operation is ensured with water curtain drill holes which were drilled above the cavern from the access tunnel. The groundwater table around the cavern and in the water curtain will be regularly monitored from boreholes during the operation of the cavern. No major rock mechanics or engineering problems were met during the construction of the cavern. 1. INTRODUCTION A large new LPG cavern (Figure 1) has been built in the bedrock of Borealis Polymers production facilities in Porvoo, southern Finland. It is related to the total capacity increase of plants. Liquid propane and butane can be stored in the rock cavern, which Borealis uses as raw materials for the production of polyolefin plastics. Polyolefin plastics manufactured at the Borealis Porvoo plant are mainly used as raw material for water, gas and wastewater pipes, steel pipe coatings, electrical cables and packaging.

ABSTRACT This paper describes the detailed numerical analysis performed to study and observe the effect of toe cutting caused by anthropogenic activities like construction of new roads, widening of existing roads and by natural processes like undercutting and erosion by rivers and streams, on the stability of slopes. For this purpose, a slope showing the evidence of toe cutting caused by river erosion and undercutting is chosen for analysis. The slope selected for analysis is made up of a mixture of soil and debris material lying above the rigid hard bed rock foundation. The selected slope has been analysed using the Morgenstern – Price limit equilibrium method using the GeoStudio SLOPE/W software. In order to comprehend the behaviour of slope under different geotechnical, hydraulic and seismic conditions the analyses have been performed by taking into account a wide variation in these parameters. The behaviour of slope and its probability to failure is calculated on the bases of the evaluated strength reduction factor in different strength effecting conditions. In this study, the analyses are conducted in three different phases. In the first phase, simplified model of the slope is analysed under its own weight without any additional parameter. In the second phase, pseudo static analysis has been performed on the slope. In the third and last phase, hydraulic parameters were incorporated in the slope model and the results are generated. Results of the analysis are presented in easy to interpret graphical format and based on the analysis, results are interpreted for the critical horizontal limit of the vertical toe cutting of the slopes for the different types of slopes having varied geotechnical parameters. INTRODUCTION Toe cutting of hill slopes is a common slope destabilising phenomenon related to the routine work carried out on hill slopes in order to construct new roads or in widening of the existing roads or due to the erosion caused by undercutting of slopes by rivers. The road cutting as anthropogenic interference on hill slopes is the consequence of the advancement of the facilities and infrastructure due to rise in population and high demand of foreign resources in the hilly regions.

ABSTRACT Internal Erosion Occurs Due to the loss of Soil Particles As a result of Seepage phenomenon. Existing dam safety has been one of the most important hydro system engineer's worries and identification of serious accidents which may cause dam failure, is very crucial. To assess the probability of internal Erosion, the risk analysis can be utilized. Monte-Carlo simulation is one of the tools which can quantify the risk analysis result due to uncertainties in the Geotechnical engineering soil parameters. In the present study, the probability of dam failure and the reliability analysis of dam was estimated against internal erosion. FLAC software has been used together with Monte-Carlo simulation to Compute exit gradient and effective stress in the toe of dam. A case study, namely, Doosti Dam in Khorasan Razavi Provence, Iran has been considered. The analysis procedure also verify with instrumentation data which were installed in section 2–2. As a result and Based on the numerical analysis, it shows that the dam has above average reliability index, β=2.7, against internal erosion in outlet of horizontal drainage. INTRODUCTION In recent years, headline news has been overwhelmed with stories about dam and levee failure, which is caused by initiation erosion in body or foundation of dams, including the 2005 levee breaches in New Orleans, the 2006 Kaloko dam failure in Hawaii and the 2008 Redland Dam failure in Arizona. Since 2000, state and federal agencies have reported 92 dam failures in the United States to the national performance of dams program (NPDP, 2007). Incidents such as these have brought both national and worldwide attention to the need of prediction for embankment dam and levees failure. The two most common causes of earthen embankment and levee failure are overtopping and internal erosion (Fell et al., 2003). According to high prices of dam projects, it is more important to evaluate the workability of dams during their life. Risk and reliability are two major concepts in hydro system engineering. Reliability can be defined as a probability of non-failure. Therefore by increasing the probability of system failure the reliability of system will decrease. Estimation of system reliability needs many statistical tools because it always reports as a probability and it is necessary to have sufficient knowledge about the probability theory and statistics rules. Load forces and resistance of a system are two main part of the risk and reliability analysis. Moreover due to uncertainties in geotechnical parameters evaluating of load and resistance are complicated. Monte-Carlo simulation is one of the practical tools for estimating these parameters to analyzing risk and reliability. In this paper first we proceed Internal Erosion Background and Reliability analysis, after that by using Finite difference program (FLAC) with help of Monte-Carlo simulation we evaluate the Reliability of Internal erosion in Doosti dam.