JOURNAL OF ROCK MECHANICS
Year:2017 | Volume:1 | Issue:1 |Papers Count:9

Summary In this paper, the influence of three different parameters (confining pressure, particles shape and mode of failure) on particle breakage in granular media is studied by discrete element method. The percentage of particle breakage under four confining pressure levels is presented for three particle shapes and two modes of failure. At last, the results are compared with the past numerical and experimental outcomes and the weak and strength points are evaluated. Introduction According to the results of experimental tests, various parameters are effective on the behavior of granular materials. In this paper, the effect of confining pressure, grain shape and modes of failure on propagation of particle breakage in granular materials has been investigated. To achieve this, numerical simulations of biaxial tests are implemented by DEM. The numerical methods are not only cheaper and faster, but also more focused on one or several specific parameters. Methodology and Approaches To model the biaxial tests, the modified DEM code POLY (which is a Fortran code) was utilized. For each of the three mentioned parameters, the results of numerical simulations are represented in terms of curves of particle breakage percentage against confining pressure. The numerical tests are performed for three different particle shapes (triangular, square and hexagonal particles) which can be broken in two modes (fragmentation into two halves or erosion of the angular points). Results and Conclusions The outcomes show that an increase in both angularity and confining pressure parameters leads to an increase in particle breakage of the samples. Also, the mode of failure has a considerable effect on the percentage of particles breakage. Finally, the results of the numerical modeling with the discrete element code utilized in this study are compared with the past numerical and experimental outcomes in one figure; a comparison between the results shows their acceptable agreement. There are also some differences between the outcomes which may be originated from quite a few reasons, two of which are as follows: 1. The numerical simulations, unlike the real tests, are two dimensional and 2. The methodology of defining breakage is different for numerical and experimental tests. In overall, utilizing the present code for the future studies will be logical.

Summary One of the possible choices for the foundation of large scale structures like dams and bridges is to build it on rock masses. In comparison with soils, most rocks have more strength-and that means more bearing capacity. So, the load of structures on rock mass usually causes no problem from bearing point of view. One of the terms of safe application of foundations is to bear the load structures or in the other hand bearing capacity of foundation is adequate for load structures. Estimating bearing capacity of foundations has been one of the most important problems for geotechnical engineers and because of its importance; several relations have been suggested with different researches. A typical method in design of structures in geotechnical engineering is safety factor that is a stuffy method and even in most cases lead to increase in project costs. However, not paying attention to the reliability of soil or rock parameters, even in a small scale, and using just a number as safety factor is not logical. Reliability and error is a common problem in geotechnical engineering and especially in rock mechanics. So, using reliability methods in geotechnical engineering has been common. In these methods, by using a range of probable values for parameters, variation of the function will be determined. Since using probability methods especially in geotechnical engineering is so limited, in this study, the most common method for reliability analysis “ Monte Carlo” was introduced and reliability relations for bearing capacity of footing on rock masses was proposed. Using the proposed method in this research, bearing capacity of a strip footing on rock mass located in Ankara (Turkey) was studied and finally, the accuracy of results from different probabilistic methods is compared with results of deterministic method. The modified Hoek-Brown failure criterion was used to study the bearing capacity. Finally, a probability distribution of the bearing capacity was estimated and the probability of failure was calculated.

Summary This paper is aimed to introduce the Longitudinal Deformation Profile of supported tunnel. Tunnel depth, RMR value, coefficient of lateral pressure along with support stiffness and non-supported length behind the tunnel face are selected as main effective parameters. Tunnel support may be concrete or shotcrete. To obtain the supported LDP curve which is known as SLDP, FLAC3D numerical code is utilized. Statistical processing of numerical experiments allows us to drive some relations, characterizing different parts of SLDP curve. Results show that existence of lining changes the shape and magnitude of deformation profile. Introduction Considering the importance of underground structures, selection of a suitable location for support system installation behind the tunnel face is of a great importance for stability analysis. The usual way to solve this problem is the application of LDP, one of the three tools of Convergence-Confinement method. The LDP is the graphical representation of the radial displacement that occurs along the axis of an unsupported cylindrical excavation for sections located ahead of and behind the excavation face. Many researchers, such as Panet and Guenot (1982), Panet (1993, 1995), Chern et al. (1998), Hoek (1999), Unlu and Gercek (2003), Vlachopoulos and Diederichs (2009) have suggested elastic or elastoplastic relations for the LDP. Anyway, these solutions do not incorporate the stiffness of support in the deformation profile. Other researchers including Bernaud and Rousset (1992), Nguyen-Minh and Corbetta (1991), Nguyen Minh and Guo (1993) and Bernaud and Rousset (1996), Vardakos (2007) discussed the effects of the support mechanical or geometrical characteristics in the deformation profile. Methodology and Approaches In this research, the LDP of supported tunnels was modeled using FLAC3D software and assuming the following conditions: non-circular lined tunnel in elasto-plastic rock mass with different RMR values (40-70), depth of overburden from 100 to 300 m, three values of in situ stress field (0. 5, 1 and 1. 5), changing length of non-support interval from 1 to 5 m and different support stiffness. In order to differentiate supported LDP from non-supported one, it is named SLDP. In SLDP curves, deformation profile has a hump shape between the tunnel face and support edge. Also, the ultimate deformation of supported profiles is less than the non-supported ones. Based on the statistical processing of huge number of numerical modeling results for different combination of above mentioned parameters, a series of relations for calculation of different parts of SLDP were presented. Results and Conclusions The SLDP profile and given equations can be used to determine the final displacement and the displacements in the important points of non-supported interval, including tunnel face, at the peak of hump and edge of support system, however, the newly presented concept-SLDP is more practical than LDP for tunnels under construction. In addition, existing equations concerning supported tunnels are only applicable for circular tunnels under hydrostatic condition, while the presented equations are valid for non-circular tunnels under hydrostatic and non-hydrostatic conditions.

Iran has the first world's gas reserves and the fourth largest oil reserves, which most of them are located in the sandstone reservoirs. In fields such as Mansoori, Ahvaz and Rag Sefid have more problem of sand production than other reservoirs. This problem should be investigated for these reservoirs. Summary The problem of sand production as one of the major challenges has attracted many researchers over the years. In this regard, many techniques have been developed and significant evolutionary growth. Some of these methods are laboratory, analytical and numerical methods. The effect of various parameters on the sand production is studied by using these methods. The best approach is three-dimensional modeling of sand production due to the complexities of this problem. In this paper, threedimensional modeling is done in PFC3D software. The results showed that sand production is raised with increasing of confining pressure. Introduction Studies show that many factors affected on the failure and separation of sand grains from reservoir rock. The prediction of sand production is very complicated, because of the combination of hydrodynamic and geomechanical processes in the mechanism of failure, erosion and transport of grains at the same time. One of the methods for examining of the mechanism of sand production in the well is numerical modeling of reservoir rock and fluid flow with integrated solving of fluid and rock equations. One of the parameters in the sand production is confining pressure, in other words earth lateral pressure that the effect of this parameter should be studied. Methodology and Approaches In this paper, the effect of confining pressure was investigated by using Discrete Element Method in PFC3D software. The Navier-Stokes equation is used for modeling of fluid flow between the particles and the effect of liquid on solid particles in the path of fluid flow is considered in each of the elements. At the first, the numerical results were compared with experimental model. The impact of confining pressure on sand production is investigated after validation of the numerical. Results and Conclusions Sand production rate in numerical models has a good agreement with experimental results in the wells without gravel pack. Numerical results showed that rock around the wells are loosed with beginning of the sand production and loosed region is expanded with increasing of production. The results also showed that the weak formations, that confining pressure is high, are more stimulated compared with the formations have less stress. So, sand production is risen with increasing confining pressure.

Summary An approach based on the failure modes and event analysis (FMEA) was developed considering a three-member team of blasting experts in order to assess the ground vibration risk resulted from blasting. Fourteen states of occurrence were considered focusing the impacts of ground vibration on the infrastructures and structures of Sungun mine. Through statistical analysis, a relation was provided to determine the minimum vulnerable distance from a blast source. After presenting the qualitative and fuzzy number ratings of the risk factors, the fuzzy number of each 14 states was determined together with the fuzzy weights of each factor according to the ideas of experts. The fuzzy risk priority numbers of the states were calculated considering the geometric mean of the fuzzy weights. Results indicated that the states C-4 (industrial site), F-9 (gas station), and G-10 (treatment site) have high risk values. Crusher (A-1) and explosive storage (I-13) both had less than an average risk and the other states included negligible risk. Introduction Ground vibration as one of the undesirable consequences of blasting can impose numerous risks to open pit walls, infrastructures, and structures within or around a mine. Considering the specific conditions of Sungun mine, this problem is very sensitive. The main purpose of this research is to develop an approach in an uncertain environment based on the failure modes and effect analysis (FMEA) for particularly assessing the ground vibration risks caused by blasting. Methodology and Approaches Fourteen cases including the infrastructures and structures sites, which were under the ground vibration risks, were considered. The location of the sites was indicated on the map of Sungun area. Blasting data were statistically analyzed using SPSS software, in order to obtain a relation for determining the minimum vulnerable distance from a blast. The main process of the ground vibration risk assessment was made using the FMEA approach, which was developed by presenting the qualitative and fuzzy number ratings of the related risk factors and also by considering the fuzzy weights of each risk factor according to the ideas of an expert team. Results and Conclusions Results indicated that only the industrial site, gas station, treatment site, and almost crusher had considerable ground vibration risk; hence, they should be essentially managed in order to decrease their risk levels by employing the available solutions. Because of a long distance from the blast sources, other sites had negligible risk.

Summary In this paper, Probability Density Function (PDF) for thickness of the shotcrete cover in tunnel temporary support is investigated. Based on collected data from a recently constructed tunnel in Iran, the proper PDF is suggested. To achieve this, three goodness of fit statistical methods are considered to find the appropriate distribution function. The results show that the Generalized Extreme Value distribution function has the best rank with respect to other distribution functions. Introduction One of the most important issues in the reliability analysis of the structures is proper selection of the distribution function for existing random variables. In tunnels, the problem of temporary supporting system involves many random variables including thickness of the shotcrete. In this research, based on the data obtained from an existing tunnel in Iran, the probability distribution function for the shotcrete thickness is determined by using curve fitting techniques. Methodology and Approaches Different distribution functions have been studied and compared based on three well-known goodness of fit tests, called Chi-Squared, Kolmogorov Smirnov and Anderson Darling. For this purpose, nine points in each section and 43 individual sections are considered in the tunnel route. It is reasonable an individual point in all sections is considered to obtain a distribution function. Also, 15 types of distribution functions are chosen to have an appropriate fit over the data. The EasyFit software is utilized for assessment and finding the appropriate distribution function using the three mentioned goodness of fit tests. Results and Conclusions According to the results, the Generalized Extreme Value Distribution is recommended for PDF of shotcrete thickness in tunnel supporting systems. It is noted that this distribution function has the best rank in all three goodness of fit tests. Although the results are obtained by using data from a specific tunnel project, they can be improved by considering more data from other projects. The distribution function can be used to obtain uncertainties of thickness of shotcrete in reliability analysis of tunnels.

Schedules are major concerns in construction planning and management. The mutual interferences among construction activities of tunnels are complicated, which will affect scheduling to some degree. Ground condition and construction (excavation & support system) time and costs are key factors in decision making during the planning and design phase of a tunnel project. In this work the DAT innovative methodology for the probabilistic estimation of ground condition and construction time and costs is used. As construction progresses, geologic information is checked based on the excavated part of the tunnel and, therefore, the uncertainty about this part of the tunnel will disappears. This new information can be used to update the geology condition of the tunnel in order to obtain more precise prediction for unexcavated part. In this paper, an engineering application to Garan road tunnel is well presented to demonstrate how the ground conditions and the construction time and costs are updated during construction. Finally, the results of simulations for the initial prediction and the updated prediction will be compared in order to see how the construction time and costs distributions of the given tunnel are changed after the geologic updating. Finally, reducing of uncertainty about the construction time and costs is resulted. It facilitates both the owners and the contractors to be aware of the risk they should carry before construction of unexcavated part, and it is useful for both tendering and bidding...

Summary Knowing geomechanical parameters of soil and rock is among the important items of designing and constructing engineering structures. Deformation modulus may be determined through in-situ tests and indirect methods. For indirect estimating of this module, empirical relations are simple and inexpensive methods, but their uses in other parts of the world were associated with errors due to the variation of rock type and the nature of rock mass. In the present article we attempted to estimate the deformation modulus (Em) of the rock masses of southwestern Iran by using intact rock elastic modulus (Ei) and Rock Mass Rating (RMR) parameters. To do that, the multivariable linear regression method was used. The database used included 333 data. In order to study the relation performance and to evaluate its accuracy, R2 coefficient (coefficient of determination) and RMSE (root-mean-square error) were used. For this data R2 coefficient was 0. 811 and RMSE value was 0. 1921...