نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 25 (زمستان 1399)

The subsurface dam is considered a way to store and utilize subsurface flow in dry and warm areas. In this study, the appropriate locations for constructing a subsurface dam in an Abouzeidabad plain were pinpointed using remote sensing and geophysical methods. To this end, topography, slope, lithology, land use, stream density, fault density, and qanat density information layers were provided. In providing these layers, Digital Elevation Model (DEM) and Landsat 8 satellite images were used. Due to the importance of alluvial formations in the reservoir volume of the subsurface dam, the lithology layer in the form of a geology map subject was made to separate the formations suitable for the dam storage. Analytical Hierarchy Process (AHP) method was used to compare and evaluate the layers and substrates. A final map of location priorities for the construction of a subsurface dam was then developed using the results from the AHP method. After identifying three locations of high priority (4 to 5), the geophysical data were collected from these locations using Ground Penetrating Radar (GPR) method to determine the bedrock position and alluvium thickness in each cross-section. Using the obtained data and hydrological information of the area, discharge capacity was calculated for each of the identified locations. At the most appropriate location, a subsurface dam with 311 meters length and 17 meters depth was proposed to reach the discharge capacity of over 4.35 million cubic meters, which is considerable for supplying the water demands of downstream regions including Badroud and Abouzeidabad.

Representative Elementary Volume (REV) size study was carried out for data of Sechahoon Anomaly XII mine by using a discrete fracture network and distinct element method to characterize mechanical and behavioral properties of a highly jointed rock mass. By studying on scale dependency of mechanical properties of the rock mass, REV size was determined. On the other hand, for continuum modeling of rock mass because of the inherent uncertainty in geometrical and mechanical characteristics, 39 sample models were generated stochastically based on geometry variation of joints. Uniaxial and triaxial compressive tests were performed and finally, distributions of UCS, deformability modulus, cohesion, and friction angle of rock mass were obtained. These can be used for reliability and probability investigation of the rock mass.

It is well-known that the mechanical behavior of rocks under cyclic loading is much different from static loading conditions. In most constructions, the load applied to structures is within dynamic ranges. That’s why a great deal of attention has been paid to this field to identify the dynamic behavior of rocks in more detail. Nevertheless, the nature of dynamic failure in rocks has not yet been identified, particularly when it comes to cyclic loading The purpose of this study was to investigate the influence of grain size on the mechanical behavior of rocks under cyclic loading using numerical modeling by UDEC. A total of three grain-categories with a diameter of 1, 2, and 4 mm were modeled in the software. All models were of Brazilian type with 54 mm diameter. Behavioral parameters required for modeling were determined through laboratory studies and the software was adjusted accordingly. The stresses applied to the samples were in two forms of quasi-static and cyclic loading. The result of static loading is that the smaller the grain size, the model will have a higher elastic modulus. In other words, the elastic modulus of the grain size is inversely related to the grain dimensions. Analysis of data obtained from cyclic loading showed that the amount of strain in samples with smaller grain sizes was lower than the corresponding strain in samples with larger grain sizes during the same loading periods. In other words, the resistance of samples with smaller grain sizes to deformation under cyclic load was higher compared to those with larger grain sizes. Comparison of the stress vectors for these samples showed that with a decrease in grain size, stress distribution in the sample became more uniform and inclusive, and the stress concentration declined. Another important result was that the smaller the grain size, the more the axial stress applied to the sample inclined towards one. This indicated that with a decrease in grain dimensions, the sample behavior approached a plastic behavior.

Power spectrum – area fractal (S-A fractal) method has been frequently applied for geochemical anomaly mapping. Some researchers have performed this method for separation of geochemical anomaly, background and noise and have delineated their distribution maps. In this research, surface geochemical data of Zafarghand Cu-Mo mineralization area have been utilized and some defects of S-A fractal method have been discussed. The surface geochemical data were transformed to the frequency domain using Fourier transformation and the S-A fractal method was performed on obtained Cu power spectrum. 4 geochemical classes were distinguished on the basis of fractal diagram then these classes were separated using various filters and their signals were analyzed separately by principal component analysis (PCA) and the situation of mineralization was interpreted. PCA shows the low frequency geochemical signals have strongly been affected by the Cu and Mo mineralization process. In the end, the Cu geochemical anomaly map based on this low frequency class was delineated using inverse Fourier transformation. The deep borehole that was drilled in the center of this obtained anomaly shows there is a mineralization zone at the depth. The disadvantages of S-A fractal method have been discussed using these obtained results.

One of the most widely used methods for the excavation of metro tunnels is mechanized excavation using an earth pressure balance (EPB) boring machine. Predicting the penetration rate of the boring machine can significantly reduce costs in mechanized excavation. Geological and geotechnical factors, machine specifications, and operational parameters can be influential on the penetration rate of the machine. Important geotechnical factors include cohesion, friction angle, and soil shear modulus. Among the important machine parameters, the thrust force of the jacks, the torque, and the rotational speed of the cutter head can be mentioned. In this study, after analyzing the main component, eliminating the outlier data, and normalizing the data, by considering the geotechnical factors and various parameters of the mechanized boring machine, the penetration rate of the EPB machine in the Tabriz metro line 2 tunnel has been predicted. For this purpose, linear regression methods, fuzzy logic using Mamdani and Sugeno algorithms, neuro-fuzzy method, and metaheuristic algorithms were used. To validate each model, statistical indices of the coefficient of determination (), root mean squares error (RMSE), and performance indicator (VAF) were used. The results of the studies showed that the neuro-fuzzy method has a better prediction of the penetration rate in comparison to other methods. Also, the results of the sensitivity analysis revealed that the cutter head torque had the greatest effect on the penetration rate of the EPB machine.

In this paper, the effect of cable indent shape on the shear behavior of concrete-cable attachment surface has been investigated using PFC2D. Firstly, calibration of PFC was performed using the Brazilian experimental test and uniaxial compression test to reproduce the concrete sample. After calibration of PFC2D, punch shear tests were simulated by creating a rectangular concrete model in PFC2D. Numerical models with a dimension of 100mm *100 mm were prepared. cable with different indent shape was inserted within the model. The punch shear test condition was added to the model. The normal load was fixed at 3.7 MPa (σc/10) and shear load was applied to the model till failure occurred. The results show that tensile cracks are the dominant mode of failure that occurs in the attachment surface.  Also, the shape of the attachment surface has an important effect on the failure mechanism of concrete. The shear strength increased by increasing both of the bolt indent width and length.