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Abstract: One of the most important goals of the experiments is to determine deformation and strength of the rock specimen under applying triaxial load. The status of failure condition is one of the subjects, which can be used in soil mechanic and foundation engineering applications. To investigate the effect of confining pressure on the triaxial test, the rock was considered as bonded-particles method and simulated by PFC3D program. To compare the mechanical behavior and failure pattern of the numerical and experimental results at uniaxial and triaxial tests at the same conditions, the Young's modulus, Poisson's ratio and maximum axial stress were considered. On the other hand, the microcracks growth and change of failure pattern at the modeling of the uniaxial and triaxial tests with different confining pressures up to failure point were reported. According to the experimental work, the number density of microcracks decreases from starting value and remains almost constant up to the failure beyond that point. Comparison of the numerical and experimental results of maximum axial stress and the Poisson's ratio revealed a good accordance. The simulated Young's modulus was smaller in comparison with the experimental ones and the difference was about 36%, which seems to be due to absence of the pre-existing microcracks on the model. The initial number density of microcracks at the model was zero and increased while microcracking. Also the sudden increment around the maximum stress was observed, which is because of unstable growing of microcracks near the maximum stress. In all uniaxial and triaxial tests with different confining stresses, the number density of microcracks during the failure remained almost constant, which can be considered as a proof of failure occurring in the model. The experimental results indicated a similar trend as well.

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Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. Discontinuities in the media and their mechanical properties greatly affect the geometry and propagation of hydraulic fractures. In this research, the interaction between the hydraulic fractures with the media layers interface, fracture propagation pattern and termination in multi-layered media were investigated. The true tri-axial cell was utilized to conduct experimental tests on cube multi-layered samples with discontinuities. The tests were aimed to investigate propagation of fractures from soft to stiff, stiff to soft media and also the effect of elastic properties of rocks in hydraulic fracturing. Results showed that the condition of discontinuities (healed, open or filled) and elastic properties of the layers influences the geometry and propagation pattern of hydraulic fractures. In the block with the bounded interfaces, the fracture propagates and interacts with the interfaces, then penetrates in the adjacent layers. However, for the block with unbounded interfaces the fracture propagates from the borehole up to the interface, then after filling the interface with the fluid the new fracture will propagate in the adjacent blocks. In sample where the interface was filled, the fracture propagation was terminated and then the fluid started to leak off in the interface. The results also show when the fracture reaches the interface, the pressure increased immediately and more pressure is needed for fracture propagation across the interface. In comparison between the length and width of fractures in soft and stiff layers, the study displays that the fracture width and its penetration length in soft layers are greater than those in stiff layers.

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Determining the bearing capacity of piles is an important issue that always Geotechnical engineers focus on. Effect of factors such as environmental dissonance of soil which contains a pile, pile implementation, pile gender and its shape make correct estimation of bearing capacity difficult. Pile load testing as a reliable method could be used in various stages of analysis, design and implementation of piles to determine the axial bearing capacity of piles. On the other hand, pile load testing, despite high accuracy, imposes high cost and long duration for development projects and it causes limitations in this experiment. Thus acceptance of numerical analysis at geotechnical studies is increasing. In this study serious models of multi-layer perception neural network, one of the most commonly used neural networks, was used. In all models four parameters are used as input data which are length and diameter of the pile, the coefficient of elasticity and internal friction angle of soil and the bearing capacity of piles is used as output data. Models have reasonable success in predicting the bearing capacity of piles. To increase the accuracy of predicting bearing capacity, for the network training stage the real tests that has been done at the geotechnical studies of dry dock area Hormozgan by POR Consulting Engineers were used. According to (Because we) need of more data for training and testing network, several tests on pile bearing capacity, in smaller dimensions were performed in the laboratory. To perform these tests the device of pile bearing capacity, made in university of Tarbiat Modarres, was used. Models based on neural networks, unlike traditional models of behavior don’t explain effect of input parameters on output parameters. In this study, by the sensitivity analysis on the optimal structure of introduced models in each stage it has been somewhat trying to answer this question.

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Abstract: Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. Discontinuities in the media and their mechanical properties greatly affect the geometry and propagation of hydraulic fractures. In this research, the interaction between the hydraulic fractures with the media layers interface, fracture propagation pattern and termination in multi-layered media were investigated. The true tri-axial cell was utilized to conduct experimental tests on cube multi-layered samples with discontinuities. The tests were aimed to investigate propagation of fractures from soft to stiff, stiff to soft media and also the effect of elastic properties of rocks in hydraulic fracturing. Results showed that the condition of discontinuities (healed, open or filled) and elastic properties of the layers influences the geometry and propagation pattern of hydraulic fractures. In the block with the bonded interfaces, the fracture propagates and interacts with the interfaces, then penetrates in the adjacent layers. However, for the block with unbonded interfaces the fracture propagates from the borehole up to the interface, then after filling the interface with the fluid the new fracture will propagate in the adjacent blocks. In sample where the interface was filled, the fracture propagation was terminated and then the fluid started to leak off in the interface. The results also show when the fracture reaches the interface, the pressure increased immediately and more pressure is needed for fracture propagation across the interface. In comparison between the length and width of fractures in soft and stiff layers, the study displays that the fracture width and its penetration length in soft layers are greater than those in stiff layers.

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The cone-penetration test (CPT) is a well-established in situ test in geotechnical engineering for soil classification and estimation of soil properties. In a CPT, a cone shaped penetrometer is pushed into the ground at a constant rate. The resistance on the cone tip is measured and is then related to soil classification and soil properties. In this research, the finite difference analysis of large deformations for the cone penetration testing (CPT) in the cohesive soil have been conducted using FLAC 2D Software. In this modeling, interface elements between penetrometer and soil are considered and it is assumed that the penetrometer materials show rigid behavior in reaction to the soil materials. FLAC provides interfaces that are characterized by Coulomb sliding and/or tensile separation. Interfaces have the properties of friction, cohesion, dilation, normal and shear stiffness, and tensile strength there is an in-situ state of stress in the ground, before any excavation or construction is started. In FLAC 2D, an attempt is made to reproduce this in-situ state by setting initial conditions. Ideally, information about the initial state comes from field measurements. Boundary conditions are modeled as axesymmetry. Horizontal and vertical direction at the bottom boundary and horizontal direction at the vertical boundary of soil model are fixed. Soil behavior follows full elastic–plastic model and Mohr-Coulomb failure criterion. Numerical model is analyzed to achieve mesh convergency at the various grids. The values of cone and frictional resistance have been obtained through software calculations and then compared with the results obtained from cone penetration test at the aluminum melt factory in Lamard, Fars Province. Stress and displacement contours are related for evaluation of the penetration process. Steady state is considered to achieve steady stress range in which the hole diameter is equal with the CPT hole. The numerical modeling results of CPT test by FLAC 2D software shows good agreement with the field tests results. Furthermore, the results have been discussed by using Robertson Chart 1986 and Eslami- Felonious Chart 1997. Charts almost show same profile with the field test results at the aluminum melt factory site.

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The lateral spreading of mildly sloping ground and the liquefaction induced by earthquakes can cause major destruction to foundations and buildings, mainly as a result of excess pore water pressure generation and softening of the subsoil. During many large earthquakes, soil liquefaction results in ground failures in the form of sand boils, differential settlements, flow slides, lateral spreading and loss of bearing capacity beneath buildings. Such ground failures have inflicted much damage to the built environment and caused significant loss of life. The risk of liquefaction and associated ground deformation can be reduced by various ground improvement methods, including densification, solidification (e.g., cementation), vibro-compaction, drainage, explosive compaction, deep soil mixing, deep dynamic compaction, permeation grouting, jet grouting, piles group and gravel drains or SCs. Nowadays, using pile foundation is one of the popular solution for soils vulnerable to liquefaction. the pile with enough length more than liquefiable soil depth can reduce the large deformation and unacceptble settlements. Liquefaction and lateral deformation of the soil has caused extensive damage to pile foundations during past earthquakes. Several example of significant damages in pile foundation have been reported in the literature from the 1964 Niigata,1983Nihonkai-Chubu,1989 Manjil and 1995 kobe earthquakes. These damage have been observed mainly in coastal areas or sloping ground. evaluation of liquefaction in order to develop the northern and southern ports and implement coastal and offshore structures in Iran is of particular importance due to locating in a high seismic hazard zone and Liquefactable soil in coastal areas. Although, in recent years many studies have been conducted to understand the various aspects of this phenomenon, yet a lot of uncertainties have remained about the lateral deformations of the soil and its effects on deep foundations. In this study, behavior of pile groups (2 × 1, 1 × 3, 2 × 2 and 3 × 3) were evaluated using fully coupled three-dimensional dynamic analysis. Therefore, the influence of effective parameters such as number of piles, ground slope angle on soil and pile behavior has been studied using the finite element software Opensees SP v2.4. results indicate that most of the factors affecting the behavior of the pile, soil are not considered in the current design codes (such as JRA 2002) and these issues indicate the need to revise the current design and analysis methods.Lateral Pressures compared to that of JRA regulations show that these regulations cannot exactly predict pressures on pile and pile groups. Altogether comparing the results of numerical model of this research to various laboratory observations indicate that the use of numerical method can be reliable to predict the behavior of the soil and pile qualitatively and quantitatively using appropriate constitutive model and parameters for soil and pile. Keywords: Liquefaction soil, pile group, fully coupled numerical analysis, multi-surface-plasticity constitutive model.

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  In the recent years, new techniques such as artificial neural networks were used for developing of the predictive models to estimate the needed parameters in Geotechnical Engineering such as swelling potential. If over 50% of the particles in a sample are able to pass through a number 200 screen or sieve then the sample is classified as either silt or clay or some combination of both. Regardless of the percentage of “fines” in a particular sample, a significant presence of clay minerals in a sample can indicate a possible expansive soil problem. When they absorb water they increase in volume. The more water they absorb the more their volume increases. Expansions of ten percent or more are not uncommon. This change in volume can exert enough force on a building or other structure to cause damage. Cracked foundations, floors and basement walls are typical types of damage done by swelling soils. Damage to the upper floors of the building can occur when motion in the structure is significant. Expansive soils will also shrink when they dry out. This shrinkage can remove support from buildings or other structures and result in damaging subsidence. Fissures in the soil can also develop. These fissures can facilitate the deep penetration of water when moist conditions or runoff occurs. This produces a cycle of shrinkage and swelling that places repetitive stress on structures. Determination of swell potential of soil is difficult, expensive and time consuming and also involves destructive tests. Multi-layer Perceptron model is one of the most sufficient methods of the Artificial Neural Networks in most of the research applications in engineering etc. In this research, Multi-layer Perceptron model and Radial Basis Function model of ANN (artificial neural networks) were used in order to predict expansive behavior of clayey soils (i.e., swell percent). All data have been modeled by using many types of architectural Multi-layer Perceptron network. Then, the output result of these networks are compared with each other according to the assessment indexes which has been leaded to the best architectural network selection in viewpoint of accusation and usage. It is noticeable that the parameters such as Natural Water Content, Plastic Index, Dry Density and Fine Soil Percent are considered as input parameters and swell percent (S%) is considered as output parameter. The Soils which are selected for this research is clayey soils from different areas of Iran. Consequently this ANN has the ability to predict expansive behavior of diverse types of clayey soils. To train this network, results of previous researches, geotechnical consultant engineering data and the available thesis about Expansive soils are used. It was found that the Multi-layer Perceptron (MLPst and MLPdy) models exhibited a higher performance than Radial Basis Function (RBF) model for predicting expansive behavior of clayey soils. Also, the comparison of the MLPst and MLPdyn network models indicates that their accuracies are almost the same. However, the time taken by MLPst is less than that of MLPst in this study. Since the population of the analyzed data is relatively limited in this study, the practical outcome of the proposed models could be used with acceptable accuracy at the preliminary stage of design.

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From oil and gas engineering point of view, one of the challenges in low permeable or damaged wells is improving the productivity. There are different methods to increase the productivity of low permeable wells and one of the most efficient one is hydraulic fracturing. In this study, two-dimensional modeling of hydraulic fracturing using finite element method and cohesive element approach through traction-separation law has been performed. This approach avoids the singularity in the crack tip and the cohesive zone fits naturally into the conventional finite element method. Hydraulic fracture is assumed to propagate in a poroelastic and permeable medium with a constant injection rate and under quasi-static conditions and the criterion for fracture initiation is quadratic nominal stress criterion. Also as a propagation criterion, Benzeggagh Kenane (BK) approach has been considered. Two types of elements have been implemented in the model which are 4-node bilinear displacement and pore pressure reduced integration and 6-node displacement and pore pressure two- dimensional cohesive element. Cohesive elements have three degrees of freedom that two of them are in X and Y directions and one of them is pore pressure. Mesh size in the near fracture region is small enough to consider the stress and pressure distribution efficiently and avoid any problem in convergence. Meantime, to decrease the computation cost the mesh size gradually increases from fracture area to the boundaries. Also, to increase the accuracy of the model, the time steps for fracture propagation is 0.01 second. In addition, the effect of fracturing fluid has been directly included in the model which means that the fluid pressure would be applied along the fracture without any simplifying assumption. To validate the model, the results have been compared with KGD approach. The results indicate that in the initial steps the pressure at the wellbore wall is high which decreases with time significantly and eventually it gets a steady and uniform trend. In other words, in the initial steps, the fluid pressure should be high enough to overcome the hoop stress around the wellbore and after some injection periods, the fracturing fluid pressure would reach the breakdown pressure and the fracture starts to initiate and propagate. It is clearly observed that increasing the injection rate would lead to faster propagation of hydraulic fracture and in the models with higher injection rate the fracture tends to grow in the propagation direction. This indirectly means that increasing the injection rate would affect both opening and length of the hydraulic fracture which can result in increasing the productivity. The results reveal that the peak of the normal effective stress profiles corresponds to the fracture tip position, where the fracture opening is zero,and the peak value equals the cohesive strength of the material,as expected.Moreover,with increasing thedistance from the fracture tip,the stress decreases rapidly and approaches the initial stress value. The way that Young’s modulus affects the overall characteristics of hydraulic fracture implies that higher Young’s modulus would lead to longer fractures. In other words, formations with higher Young’s modulus can be fractured easily but the opening of the hydraulic fracture would reduce at the same time. This also indirectly means that Young’s modulus would play an important role in the productivity.

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Hydraulic fracturing is a new and widely used method for extracting reserves and energy resources in the depths of the earth. In the near future, due to increase in energy consumption on the one hand and depletion of energy reserves on the other, using of this method will become a necessity. One of the most important and effective parameters in this process is the pressure and how it is applied in order to create fractures and fracture progression in rock layers. Another important parameter is the interaction between pre-existing natural fractures with different angles and hydraulic fracture. 
Due to the high costs of this process, the purpose of this study is to achieve the optimal state for the maximum progress of hydraulic fracture and the lowest amount of breakdown pressure at the same time. Numerical modeling was performed in two dimensions by Particle Flow Code ( PFC ) software from Itasca company on samples of Pocheon granite rocks with brittle behavior using distinct element method. PFC software uses circular disks in two dimensions to construct and make the sample using distinct element method. These particles are in contact with each other through bonds. In this program there are walls that interact with these disks to apply load on the sample. The flat joint model is used in order to create contacts between particles, and discrete fracture network is uded to to create pre-existing natural fractures for interacting with hydraulic fracture.
Given that in the distinct element method (PFC software) our sample consists of a large number of particles in two dimensions that the general characteristics of the sample are formed based on the interaction between these particles, so we need parameters as input data to our software, existing disks and the link between them, to finally obtain the specifications of the same laboratory sample after modeling. These specifications and input data are referred to as micro parameters, and the final specifications, which are the same as our mechanical parameters in the laboratory, are referred to as macro parameters.
To find the micro parameters of the sample we use the trial and error method. Here, our modeling is based on Brazilian and uniaxial compression experiments and … performed by Zhuang et al. laboratory investigations.
Due to the limitations of PFC software for fluid flow modeling and limitations for using of CFD relationships, pressure equals to fluid pressure can be used as a new solution. In this way, by modeling a number of walls that form a complete circle with overlapping each other, and by considering the servo control mechanism, we move them in the opposite direction of their normal vectors and off-center, creating a comprehensive pressure Which is actually same as the fluid pressure. From the obtained results, it was found that with increasing the loading rate, the sample reaches the breakdown pressure and breaks in less time, but the amount of breakdown pressure increases. Also, by increasing the natural fracture angle relative to the horizon (clockwise), the specimen breaks at a lower breakdown pressure. Finally, by increasing the natural fracture distance from the center of the sample, the effect of the presence of the joint in the sample decreases and the breakdown pressure approaches the seamless state.
 

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Advancements in tunnelling technologies and ease of implementation of drilling methods in addition of other political and security issues made the construction of underground structures as an important alternative for answering the demands of population growth and the limitations of surface spaces in urban areas. Underground roads and highways, various types of tunnels and urban subway networks are the examples of underground structures being constructed and rapidly implemented in different countries. Meanwhile, for reducing negative effects to the environment, shortening the routes and improving traffic efficiency, urban tunnels should have high level of safety standards in design, construction and operation. Tunnels are considered major national projects and infrastructure investments, and huge costs are incurred around the world to build these structures. In countries located in highly active seismic zone, such as Iran, seismic researches for such important underground structures should not be ignored. The safety of such structures should be provided with respect to all loading demands and hazards issues associated with the site, including seismic loads. Reviewing seismic events in the past shows that underground structures have suffered less damage than above ground structures against seismic loads. However, in recent years, major earthquakes such as the 1995 Kobe earthquake in Japan, the 1999 Chi-Chi earthquake in Taiwan, the 1999 Kocaeli earthquake in Turkey, and the 2008 Wenchuan earthquake in China have caused underground structures to experience significant damage. There is evidence to conclude that the structural vulnerability of a tunnel in seismically active areas is an important issue but is either not yet well understood or not well assessed at the time of construction, emphasising that dynamic analysis of these structures against seismic loads is necessary. Earthquakes are likely to significantly affect tunnel performance by causing severe damage or excessive deformation of the tunnel structure. To understand the seismic-induced behaviour and performance of urban tunnels, this paper provides the state of the art in modelling studies of seismic design and assessment of tunnels. The review includes an investigation in seismic responses of real tunnels reported during past seismic events, the probable mechanisms caused damages in tunnels and physical and numerical methods used until now to either investigate those mechanisms or implemented in new designs. As an introduction, the seismic performance of tunnels affected by previous seismic events discusses first, emphasising the effective parameters in evaluation of tunnel seismic response and the relationship between the parameters, and the damage levels caused during earthquakes. Subsequently, the paper continues with a comprehensive literature review on the experimental methods used to investigate seismic-induced response in tunnels including physical testing, centrifuge tests, shaking table tests, and static tests. Analytical, quasi-static and numerical methods of dynamic analysis of tunnels and the accuracy of these methods are discussed then in details referring to some examples. The paper also reviews the effects of soil heterogeneity in the seismic response of tunnel and application of the random field for dynamic analysis of underground structures.  Examining the achievements and challenges remained in the field, the paper concludes with the existing gaps in the field to stimulate readers for doing more relevant researches.

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Once, between parties to a contract, a dispute arising out of sanctions imposed by a third country is raised before dispute resolution authority, the authority can apply the sanctions to the contract and obligation of the parties thereto as “overriding mandatory rules” only if three significant requisites are fulfilled: “application worthiness of the sanction”, “close connection between the disputed contract and enacting state” and “prevalence of the benefit of a decision to give effect to a sanction over a decision to disregarding it”. Lack of each of the requisites will preclude the application of the sanctions enacted by a third country. This research will provide an answer to this question: concerning a sanction enacted by third countries what the nature of “application worthiness requisite” is what the criteria to fulfill this requisite are. Sanctions enacted by a third country will be worth applying as an overriding mandatory rule only if the object and purpose of the sanctions require considering it. I.e., according to the standards of the state of seat (in court proceedings) and the standards acceptable by the international community (in arbitral proceedings) benefits secured by means of sanctions must be “legitimate and be worthy of protection”, and the sanction must be a necessary and proportional means to achieve its purpose as well.