failure

Over the last three decades, several methods have been proposed to assess the rockfall hazard in the highways and mines. In open-pit mines, rockfalls threaten not only human lives, but also machinery and portal structures located at the toe of highwalls. Therefore, rockfalls are one of the major hazards in open-pit mines. Qualitative or quantitative procedures can be used to distinguish between hazard classes.

Methodology and Approaches:

One of the basic methods for stability analysis of the dolomite wall, especially on rock slopes, is to assess the rockfall hazard. In this paper, a qualitative rockfall hazard assessment method, named qualitative Evolving Rockfall Hazard Assessment (ERHA) and RocFall software which is specifically developed for the assessment of rockfall hazards, is used. In this method, based on the visual monitoring system, unstable blocks are recognized and Rockfall hazard is evaluated. In the study, the dolomite wall Golbini 7 Mine was divided into 13 different zones and in each zone, blocks prone to instability were identified. The total number of the evaluated blocks is 46 cases. All blocks analyzed by qualitative rockfall hazard assessment method and RocFall software.

The blocks related to zone 8 have a medium to high risk level and all blocks related to zone 13 have a high hazard level. No block is at the low hazard level. Only 2% of the assessed block are in the low to medium hazard level. 9% are in the medium hazard level, 50% are in the medium to high hazard level and 39% are in the high hazard level. The rockfall distance from the toe of the face determined by the evolving rockfall hazard assessment method and the results are compared with the modeling results by RocFall software. The maximum difference between the results is 25%.

There are various failure criteria for true triaxial stresses, which have initially been developed for the fracture of solid material such as metals. These criteria are applied for the stability analysis of wellbores and some storage caverns in rock media. In this research, true triaxial failure criteria has been investigated comprehensively by a new method using 12 groups of true triaxial strength test results of rocks including granite, monzonite, amphibolite, andesite, dolomite, Limestone, trachyte, marble, sandstone and shale. The Von Mises and Murrell criteria would not fit the test results due to their particular forms. Neither, Drucker and Prager criterion would fit the test results because of non-correlation between its defined parameters and the mechanical properties such as internal friction angle (ϕ). The relationship between octahedral shear stress (toct) and octahedral normal stress (σoct) having a constant exponent is shown to fit well the various groups of test results. The coefficient of this new criterion (B) that has been obtained by functional fitting is in good correlation with the parameters of ϕ, mi and σci. The power function relationship between toct and the mean of minimum and maximum principal stresses (σm,2) is found to be have a constant exponent also showing a good correlation with the various test results. The coefficient of this criterion (B') showed a good correlation with the parameters of ϕ, mi and σci., too. The linear relationship between toct and σoct of true triaxial strength test results was analyzed. A linear failure criterion was obtained to fit the 12 groups of results, as acceptable correlations have been obtained between the constant and coefficient of this new criterion with the mechanical properties such as internal friction angle (ϕ) and cohesive strength (C). Mogi-Coulomb linear criterion (relationship between toct and σm,2) also fitted the results and an acceptable correlation has been obtained between the defined constant and coefficient parameters of this criterion with the mechanical properties. The linear failure criteria are preferred that is because of having the constant parameter which is a function of mechanical properties of internal friction angle (ϕ) and cohesive strength (C).

Summary: In this research, stability analysis and probability assessment of the further failure for Angooran lead and zinc mine have been investigated. To investigate its geomechanical properties precisely, main joints and available faults were appraised and some samples of the mine limestone zone were prepared to determine strength properties of rocks using laboratory tests. Then, the 3DEC code was used to construct a three dimensional model. According to the initial displacements from the software and geomechanical properties of the eastern wall and its concave shape, this wall was supposed to be stable. Further analyses were focused on the western wall. For stability analysis of the western wall, the model was constructed based on different cohesions and internal friction angles. It was observed that the magnitudes of displacements were higher than in the eastern wall. So, statistical analysis was performed on the toe of the wall and the probability of the failure calculated to 35.2 percent, according to the obtained displacements.
Slope stability is one of the major and determiner parameters in the economy and safety of open pit mines. Failure and consequently rupture of the slope caused no compensable economic and humanity losses. So, probability assessment of the further failure for presentation of damages and additional costs is of prime importance. In this research, stability analysis and probability assessment of the further failure for Angooran lead and zinc mine have been investigated.
Methodology and Approaches: To investigate geomechanical properties precisely, main joints and available faults were appraised and some samples of the mine limestone zone were prepared to determine strength properties of rocks using laboratory tests. Then, the 3DEC code was used to construct a three dimensional model. According to the initial displacements from the software and geomechanical properties of the eastern wall and its concave shape, this wall was supposed to be stable. Further analyses were focused on the western wall. For stability analysis of the western wall, the model was constructed based on different cohesions and internal friction angles.
Results and In this research, field and laboratory studies were carried out in order to achieve accurate data of Angooran lead and zinc open pit mine. According to the obtained displacements of the model, probability of heavy failure was evaluated. The results are listed below:

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. It was revealed that the failure mechanism in the wall of thick-walled hollow cylindrical specimens for stress condition of is shear failure which occurs in two opposite points on the borehole wall. However, in the stress condition of 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.