دانه بندی

Blasting operation is one of the most important and costly operations in the mining process. Blasting is the beginning of the rock comminution system in the mine. The dimensions of the blasted product will play a significant role in the ability of stone crushing and grinding, for this reason, to produce a product with suitable dimensions, it is first necessary to obtain sufficient knowledge of the physical, mechanical, and chemical conditions of mineral blocks. In this research, by studying 26 iron ore blocks of the Chogharat mine, after the blasting operation, the physical, mechanical, and chemical characteristics of the ore blocks were taken. In the following, after blasting operation, by taking pictures from surface of the exploded block, an image analysis of the dimensions of blasting product was carried out. In the next step, stone samples were taken from the surface of the fired block to conduct geomechanical and chemical tests. After conducting the tests, the relationship between the physical, chemical, and mechanical characteristics of the tested stones with the dimensions of the Blast products (D50) was investigated. The characteristics examined in this study include uniaxial compressive strength, modulus of elasticity, Poisson's ratio, indirect tensile strength, cohesion, internal friction angle, and percentage of silica, iron, and iron oxide in the Blasted block. Finally, using univariate and multivariate linear regression statistical analysis, equations to estimate the dimensions of the product (D50) resulting from the blasting using the physical, mechanical, and chemical characteristics of the rock masses of the explosive product. With coefficients of determination (R2) 92.48% for D50 were predicted...

In this study, using the DEM (which exhibits suitable abilities to simulate the mechanical behavior of discrete media), the bearing capacity of a stone column has been modeled. The results showed that increasing the diameter of the stone column increases the bearing capacity and the trapped stone column has between 25 to 30% more bearing capacity than the floating stone column. 

It is necessary to study the actual behavior of stone columns in different boundary conditions and soils and against incoming loads. In this regard, researchers have used laboratory tools to study the performance of these columns. However, due to some limitations of laboratory methods, it is impossible to control all effective microstructural parameters in understanding stone column behavior. In this regard, some numerical studies based on the continuum mechanics were performed. Numerical modeling based on the mechanics of continuous media has provided valuable results on subsidence, lateral deformation, and stress-strain diagrams based on macroscopic behavior. However, stone columns are generally composed of washed sand materials and their behavioral nature is distinct sometimes their behavior depends on the performance of their particles in interaction with loose soil particles and it is not possible to accurately evaluate the performance of stone columns using finite element modeling. The discrete component method has been considered as the purpose of this research. 

The dimensions of the model were selected due to the limited number of particles due to the increase in the time of analysis on the scale of the laboratory physical model. These dimensions are determined in such a way that, with a scale of 20 times, they are similar to real projects and represent the diameter of a column of 1 meter with a length of 6 meters in reality. To eliminate the effects of lateral borders on the results, the distance of the borders from the center of the stone column was considered to be 5 times the diameter of the column. A behavioral model with rolling resistance was used. 

The modeled stone column is a tall stone column. Because the soil around the stone column is loose, the failure of the stone column is in the form of lateral expansion, which in this form is the tendency of the main force chains. The tall stone column, without lateral restraint, which rests on the trapped end and the forces are transmitted along with them, acted like a tall and thin column, which if its axis exceeds the thinness of the column. The buckle follows it. Evaluation of the behavior of the stone column can be simulated with the DEM, and micro-mechanical evaluations, especially the buckling of force-carrying chains and the path of particles can be observed. Also, the reduction of particle size has limited effects on reducing the bearing capacity of the loose stone-soil column complex.