فصلنامه مهندسی معدن
پیاپی 21 (زمستان 1392)

In most of the criteria and constitutive models presented for the shear behavior of rock fractures، only the two mechanisms of shearing through the surface asperities، and sliding along the asperities have been considered. However، the deformation of asperities before and during the shearing process is an important mechanism influencing the behavior of rock joints. The contribution of each mechanism to the shear behavior of rock joints varies depending on the morphological، mechanical، and stress conditions. In this research، a large number of concrete and plaster replicas of natural rock joints in seven groups of mechanical properties and in four degrees of surface roughness were constructed. In order to study the behavior of surface asperities، the replicas experienced CNL direct shear tests under four different values of normal stress. The results of 110 direct shear tests showed that under low normal stresses، the joints with lower wall compressive strength mobilize higher shear strength. While the previous studies of the joint shear behavior had supposed that for all the values of the normal stress، the shear strength increases as the wall compressive strength increases. The observed phenomenon، which is in contrast with the previous findings، can be described considering the contribution of different mechanisms in the direct shear tests. The effect of parameters of joint surface roughness، joint wall compressive strength، normal stress، deformation modulus، and basic friction angle on the damaged area of rock joints were then investigated. Finally، based on the statistical analyses of the test results، equations were derived to predict the damaged area.

Limit equilibrium method is one of the methods for stability analysis which is based on the stresses on the fracture plane. Stresses on the fracture plane are estimated based on the linear Mohr-Coulomb and non-linear Hoek-Brown criteria but، resulted data differ from the real stresses on fracture plane. Hence، determining the stresses on the fracture plane is considerable for the rock mechanics researchers. In the present paper، stresses on the fracture plane in brittle rocks are investigated using Coulomb theory and concept of Mohr circle. First، fracture plane is determined based on the Coulomb theory and then، using Mohr stress circle stresses on fracture plane are estimated. To validate the results، Mohr-Coulomb and Hoek-Brown criterions and Mohr stress circle which gives the real values for stresses on the fracture plane are used. Study shows that there are differences between obtained results from two criterions and Mohr stress circle، and results depend on the Mohr-Coulomb and Hoek-Brown envelopes. While according to the Coulomb-Mohr theory، stress on the fracture plane is determined using results of one experiment considering behavior of rock، and is estimated according to the real fracture plane.

Blasthole diameter and tunnel cross section are very important parameters in designing blasting pattern. Any change in these two parameters can have a significant impact on the economic and technical parameters of the design including specific charge and specific drilling. Several models have been proposed for the design of blasting patterns that can generally be categorized in two models: models based on parallel cuts and models based on angular cuts. Selection of one of these models or methods for initial design pattern is important. In this study، initially، a software is designed for Convenience of calculation. Effective parameters on blasting design such as rock and explosive properties are kept constant to study the effect of other basic parameters including blasthole diameter and tunnel cross section on parameters such as specific drilling and specific charge. Various models and methods have been studied in this research. The result show that the average blast holes number in angular method is more than parallel method for constant hole diameter and tunnel sectional area. Specific charge in parallel methods is often more than angular method. Also specific drilling، in some range of hole diameter and sectional area is higher for angular method and in other ranges parallel method Shows higher values but they are generally very close together.

This paper examines the main factors affecting transport of toxic elements from waste of leaching of Zinc leaching plant to the environment، during which behavior and solubility of heavy metals and toxic levels of Zn، Ni، Co، Cd، Mn and Pb in column leaching were investigated. Parameters included: flow rate، pH of input solution and leaching time. Filter cake highest solubility leaching was found at flow rate = 1×10-6 m3/min، pH = 5 and time = 20 days. A multiple regression analysis was applied to identify the effective parameters. Leaching time was the dominant factor on transport of toxic elements to the environment. A geostatistical commercial software called SPSS 15 was used to relate dissolution percent to flow rate، pH and leaching time. Critical situation in which toxic elements would be transported from Zinc leaching plant were determined.

In environmental impact assessment of acid mine drainage، the content determination of pyrite content and hydroxy-sulfate minerals is essential. The ASTM-D2492 standard test is an experimental method for precisely determination of pyrite and hydroxy-sulfates minerals in coal wastes. Due to mineralogical differences between coal and porphyry copper wastes، this test has to be modified for porphyry copper wastes. The main cause of error in this experiment for copper wastes is the lack of balance between acid and weight of sample in the test، thus it seems that the weight of samples have to be determined. In this study، 15 subsamples have been derived from three samples of copper waste، weighted in five levels as 1، 0. 4، 0. 3، 0. 2، and 0. 1 g. These subsamples have been tested with ASTM-D2492 standard test method and the results compared to quantitative XRD. Based on the results، the sulfur content related to hydroxysulfate minerals was independent from weight of sample and the sulfur in pyritic form was equal with quantitative XRD results in the weight of 0. 2 g. In addition، by using ASTM-2492 data، the method presented by Romero et al has been modified which became capable to indicate the environmental risk and bioavailability of toxic elements. This method was on the basis of statistical correlation analysis between ASTM-D2492 and ICP data and results in identification of toxic elements founded in hydroxysulfate minerals and adsorbed on iron hydroxides. To verify the method، 60 samples were taken from Nos. 19’s and 31’s Sarcheshmeh waste dumps and analyzed by ASTM-D2492 and ICP methods. It was found that Cd، Co، Cr، Cu، Mn and Ni were incorporated into the hydroxysulfate minerals and As، Cr and Mo were adsorbed on iron hydroxides. These results were consistent with previous studies conducted in the Sarcheshmeh copper mine using sequential extraction experiments.