JOURNAL OF ANALYTICAL AND NUMERICAL METHODS IN MINING ENGINEERING
Year:2015 | Volume:5 | Issue:9 |Papers Count:9

Using salt caverns is one of the most developed methods for fluid hydrocarbon storage. Certainty of caverns stability and simultaneously having an economical working gas ratio, are important factors that rarely have been considered in Iran. Considering salt rock characteristics and high overburden, the gravitational stress can be assumed dominant. In situ stress acts as an external pressure and causes cavern convergence. Since conventional rock supports e.g. shotcrete, rock bolt, etc. are not applicable in the salt caverns; the cavern stability can only be achieved by an internal pressure caused by the gas inside the cavern. The paper deals with salt cavern stability analysis for gas storage. Specific geometrical and geotechnical properties (with the general properties of salt domes located in the Southwest of Iran) have been modeled by Phase2 and FLAC3D softwares. Geometrical and mechanical modeling of these caverns in finite difference and finite element in desired depth, determined the minimum and maximum gas pressure for cavern stability and working gas pressure was calculated as well. Comparison of these results implies that carrot shape cavern is more economical.

In the current research, GPR response of variety of synthetic models encountered with geotechnical applications containing single horizontal cylinder, 2D prism, double horizontal cylinders, 2D arbitrary polygon and layered earth have been produced using forward modeling through the finite-difference time-domain algorithm improved in the frequency domain. In this research by using the parameters of a hyperbola and GPR responses produced for cylindrical objects by means of the forward modeling, it was revealed that there exist some linear relationships between the hyperbola height to width ratio (H/W) with physical and geometrical parameters of the cylindrical objects. These relations can be used as proper quantitative criteria to identify physical and geometrical parameters of buried cylindrical objects on GPR images. To achieve this purpose, the effect of several parameters such as geometrical shape, material type, size and burial depth of the objects as well as type and interface of fluids content and host medium physical properties on GPR responses, have also been studied. The results lead us to the potential of GPR method to detect the kinds of targets; identifying the parameters of cylindrical objects and evaluating characteristics of fluid content, so that one can distinguish metallic from nonmetallic targets as well as type of fluid content of nonmetallic targets (i.e. air, fresh water and salt water). The results of the research were validated by applying for identification of buried qanat in Shahin-Shahr plain, Isfahan province. The burial depth and diameter of the qanat were estimated by 3.4% and 12% erorr respectively.

Final model of one-dimensional magnetotelluric inversion should be consistent with geology of the region. In most sharp 1D inversion, final model is not consistent with the geology especially in the last layer. Smooth inversion such as Occam’s method often are very smooth that the thin layers are masked or difficult to model. There is uncertainty in the Larsen’s algorithm (1981), such as sharp algorithms especially the last layers. So Larsen used kernel function to overcome this problem. In the present method, the Larsen’s algorithm has been used while there are multiple layers, usually more than 10. In our method, solving kernel functions are not necessary and the depth scale is selected automatically. Finally, the method has been performed on some artificial and real data successfully.

Inverse-distance weighting method is a simple, easy and understandable interpolation in many branches of earth sciences, and it is embedded in the mining software related to estimation, Efforts to enhance the accuracy and precision of this method can be applied to a wider and reliable interpolation process. In this paper, spatial structure of different elements from analysis of rock samples associated with a porphyry copper deposit is studied using variogram. A criterion based on variogram parameters is suggested for each element to calculate the distance power. In order to validate the method, inverse-distance weighting interpolation of the different elements and different values for the inverse-distance power is implemented (common values and calculated power), error percent and root mean square error of interpolation is calculated and analyzed. Interpolation is coded in MATLAB environment and the results for different elements are demonstrated and analyzed. Based on the results, the slope of the linear part spherical variogram is measured of the amount of inverse-distance power (a) so that the values for the elements with relatively continuous spatial structure equal common values of a (1, 2 and 3) and Inverse distance weighting method is applicable for these elements.

Good estimation of fragmentation potential is very important topic before selection of caving extraction methods. In-situ fragmentation is result of discontinuities with zero tension strength but primary and secondary fragmentations happen in rock blocks that seem intact and without any discontinuity. In reality in these blocks when induced stresses (due to under cutting) or shock and stress (due to transition of rock mass) affect the blocks, weak surfaces such as rock bridges, veinlet and schistose surfaces (surfaces with tension strength) are first candidates for breakage and slice. Thus it is necessary to quantify these discontinuities in a rock mass. The purpose is to construct a way for prediction of potential discontinuities. In the next step based on necessary energy for breakage, potential discontinuities are classified. We try to design and construct a new method for quantifying and classifying discontinuities in rock mass.  This method helps us to have an initial estimate of fragmentation when induced stress and large scale displacement affect rock blocks. Rock bridges, veinlet and weak surfaces in rock like as schistose surfaces (surfaces with tension strength) are potential discontinuity. Those joints that have potential of being counted as discontinuities but are not considered discontinuity in in-situ form are put in class No, 2 versus in situ fractures (surfaces without tension strength) are classified No, 1. fractures which are created after large scale displacements are known class No, 3.

This study deals with the imputation methods of censored values in the multivariable geochemical data. Presence of the missing values causes limitation in the use of most of statistical methods, e.g. principle component analysis. Excluding the samples which include missing values bias the results and leads to the loss of information. Due to this, consideration of an appropriate approach to deal with missing values is necessary in the analysis of incomplete datasets. In this paper considering the nature of geochemical data, various approaches for imputing the missing values, which have been suggested in the recent years and are easy to be used in the R statistic software, are introduced. Finally, using the complete dataset of the Zafarghand region, these methods are compared with each other. Results show that the application of the multivariable methods in the imputation and particularly the ilr-EM method is preferable to the other methods.

Given the importance of the rock mass rating classification system in rock engineering, the aim of this paper is to improve final classes of this classification system using k-means and fuzzy c-means clustering algorithms. The data classification in the rock mass rating classification system were allocated to certain classes via a set of initial information based on the opinions and judgments of experience, which the use of clustering algorithms in this system of classification, dataset were divided into specific classes after going through the stages of clustering analysis, therefore resulting in clarification of the final rock mass rating classification systems and removal of uncertainties from the linguistic criteria. Silhouette coefficient (SC) method was used for validation k-means clustering algorithm. Furthermore, for validation of FCM clustering algorithm, four validation methods including partition distribution coefficient (PC), clustering entropy (CE), Fukuyama and Sugeno (FS) and Xie and Beni index (XB) were used. It becomes clear that due to uncertainty condition on determination of rock mass rating clustering system classes, FCM clustering algorithms yields better results than k-means clustering algorithm. Results of data extracted from Anomaly B of Sangan iron mines indicated that the technique used in this paper is of high importance in rock mass quality.

Population growth and lack of space in some cities increased the need for public transportation and implementation of subway lines. One of the most important hazards in urban area tunneling is the possible effects of the settlement on the surface structures. In this research, the effect of the main geotechnical parameters on the surface settlement has been studied. Literature show that simultaneous analysis of the parameters that affect tunnel behavior is not considered well. For this aim experimental design can be used because of its ability to make changes in input variables (geotechnical parameters) and observe the output (settlement) changes. On the other side use the expert knowledge in a Rock Engineering System is useful in order to make judgment about complex systems. For this reason, this method was also applied in order to achieve research goal. A part of Karaj Metro tunnel Line was modeled by FLAC3D in order to use experimental design. Compare the simulation results with monitoring data indicates the efficiency of numerical model in condition like this. Next, a range and sensitivity analysis was performed by using the Taguchi method. Results show that E and ν, respectively has the highest and the lowest impact on the surface settlement. The output of the rock engineering system is also show that E and ν, respectively has the highest and lowest interaction with other parameters of the interaction matrix.

In addition to high cost levels, shaft excavation in different sectors such as mining, oil and gas extraction have always been dealing with instability problems. Instability hazards can be minimized by controlling the deformation and failure of wellbore wall. The purpose of this paper is to study the deformation and failure mechanism of thick-walled hollow cylindrical specimens (for modeling of oil well) during the excavation in two different stress conditions. Laboratory tests were carried out on artificial specimens of gypsum and natural specimens of marl, sandstone and clayed limestone in order to determine the mechanical properties of the aforementioned rocks. The experiments in high stress conditions could not be carried out due to some limitations related to laboratory. Therefore, triaxial tests were done on thick-walled hollow cylindrical specimens of gypsum using modified Hoek cell. The results of tests were employed to develop and modify numerical models which were used for prediction of deformation and failure mechanisms in thick-walled hollow cylindrical natural specimens of marl, sandstone and clayed limestone in the following stress condition s1=sq>s2=sr>s3=sz. It was revealed that the failure mechanism in the wall of thickwalled hollow cylindrical specimens for stress condition of s1=sq>s2=sr>s3=sz is shear failure which occurs in two opposite points on the borehole wall. However, in the stress condition of s1=sz>s2=sq>s3=sr the failure occurs in three points with random distribution. The maximum and minimum values of borehole pressure in the failure moment occurred for sandstone and clayed limestone respectively in both stress conditions. Also the outcome of numerical modeling revealed the maximum and minimum values of plastic strain to be in cases of clayed limestone and sandstone, respectively. Pressure within the borehole at the moment of failure could be used as initial pressure of drilling fluid.