International Journal of Mining & Geo-Engineering
Volume:49 Issue: 2, Summer and Autumn 2015

Block-flexure is the most common mode of toppling failure in natural and excavated rock slopes. In such failure, some rock blocks break due to tensile stresses and some overturn under their own weights and then all of them topple together. In this paper, first, a brief review of previous studies on toppling failures is presented. Then, the physical and mechanical properties of experimental modeling materials are summarized. Next, the physical modeling results of rock slopes with the potential of block-flexural toppling failures are explained and a new analytical solution is proposed for the stability analysis of such slopes. The results of this method are compared with the outcomes of the experiments. The comparative studies show that the proposed analytical approach is appropriate for the stability analysis of rock slopes against block-flexure toppling failure. Finally, a real case study is used for the practical verification of the suggested method.

Earth pressure balance tunnel boring machines (EPB-TBMs) are favorably applied in urban tunneling projects. Despite their numerous advantages, considerable delays and high maintenance cost are the main disadvantages these machines suffer from. Reliability, availability, and maintainability (RAM) analysis is a practical technique that uses failure and repair dataset obtained over a reasonable time for dealing with proper machine operation, maintenance scheduling, cost control, and improving the availability and performance of such machines. In the present study, a database of failures and repairs of an EBP-TBM was collected in line 1 of Tabriz subway project over a 26-month interval of machine operation. In order to model the reliability of the TBM, this machine was divided into five distinct subsystems including mechanical, electrical, hydraulic, pneumatic, and water systems in a series configuration. According to trend and serial correlation tests, the renewal processes were applied, for analysis of all subsystems. After calculating the reliability and maintainability functions for all subsystems, it was revealed that the mechanical subsystem with the highest failure frequency has the lowest reliability and maintainability. Similarly, estimating the availability of all subsystems indicated that the mechanical subsystem has a relatively low availability level of 52.6%, while other subsystems have acceptable availability level of 97%. Finally, the overall availability of studied machine was calculated as 48.3%.

One of the conventional methods for temporary support of tunnels is to use steel sets with shotcrete. The nature of a temporary support system demands a quick installation of its structures. As a result, the spacing between steel sets is not a fixed amount and it can be considered as a random variable. Hence, in the reliability analysis of these types of structures, the selection of an appropriate probability distribution function of spacing of steel sets is essential. In the present paper, the distances between steel sets are collected from an under-construction tunnel and the collected data is used to suggest a proper Probability Distribution Function (PDF) for the spacing of steel sets. The tunnel has two different excavation sections. In this regard, different distribution functions were investigated and three common tests of goodness of fit were used for evaluation of each function for each excavation section. Results from all three methods indicate that the Wakeby distribution function can be suggested as the proper PDF for spacing between the steel sets. It is also noted that, although the probability distribution function for two different tunnel sections is the same, the parameters of PDF for the individual sections are different from each other.

The behavior of earth dams has particular complexities against dynamic forces and its assessment requires detailed and scientific analysis. The Farrokhi earth dam is a heterogeneous type with vertical clay core, built 150 km away from Birjand and 41 km away from Qaen on the Farrokhi River. There are concerns regarding the stability of this dam in the event of a future severe earthquake especially because of its placement near the active faults of eastern Iran, a very active seismic area in the country. In this study, the pseudo-static analysis, sliding block model and Singh et al empirical relationships were adopted to evaluate safety of the Farrokhi dam against the design earthquake. Based on the findings of the present study, the stability of the Farrokhi earth dam is not guaranteed and as such, small to large size slope failures are expected especially in the upstream side. The pseudo-static analysis and the Singh et al empirical relationships revealed similar conclusions about the stability condition of this dam, while the sliding block method underestimated the earthquake related deformations.

Metals used in everyday life are produced from ores occurring in the Earth’s crust. Geological processes are known to concentrate minerals to form ores of economic value. Mineral processing engineers concentrate these ores by mechanical and physico-chemical methods while the extractive metallurgist extracts the metals by chemical means.

In studying of the in situ gravitational concentration process part feature for placer, the technological ability to transform the in situ massif placer structure is evident. The two main processes involved in altering the massif in situ have been examined and outlined in detail. The in situ disintegration of massif material results in a new massif gravitational stratification structure. Regularities of the distribution of particles in the array of alluvial gold in situ were obtained. These regularities showed us the possibilities for direct formation of zones with elevated gold concentrations. The disintegration feature separates particles in an aqueous medium and concentrates the full exemption in situ particulate matter within the placer massif. This method will reduce the volume of mining and ore processing and increase profitability.

Lead and zinc production is one of the main predisposing factors of excessive greenhouse gases emissions, air pollution and water consumption. In this paper, the environmental problems of lead and zinc production in Calcimin plant are expressed and life cycle assessment of this plant is assessed. The data regarding the amount of induced global warming and pollution, acidification, and depletion of water resources were collected and discussed. It was concluded that depletion of water resources affected the environment and this was the main issue of the lead and zinc production of this plant. According to the results, in the global warming’s impact category, the proportion of carbon dioxide is more than that of methane. The results also showed that in the acidification’s impact category, the nitrogen oxide proportion is greater compared to that of the sulfur dioxide.

To prospect mineral deposits at regional scale, recognition and classification of hydrothermal alteration zones using remote sensing data is a popular strategy. Due to the large number of spectral bands, classification of the hyperspectral data may be negatively affected by the Hughes phenomenon. A practical way to handle the Hughes problem is preparing a lot of training samples until the size of the training set is adequate and comparable with the number of the spectral bands. In order to gather adequate ground truth instances as training samples, a time-consuming and costly ground survey operation is needed. In this situation that preparing enough field samples is not an easy task, using an appropriate classifier which can properly work with a limited training dataset is highly desirable. Among the supervised classification methods, the Support Vector Machine is known as a promising classifier that can produce acceptable results even with limited training data. Here, this capability is evaluated when the SVM is used to classify the alteration zones of Darrehzar district. For this purpose, only 12 sampled instances from the study area are utilized to classify Hyperion hyperspectral data with 165 useable spectral bands. Results demonstrate that if parameters of the SVM, namely C and σ, are accurately adjusted, the SVM can be successfully used to identify alteration zones when field data samples are not available enough.

In this paper we investigate the mechanism of internal erosion caused in the right abutment of the Shahghasem dam’s spillway. Shahghasem dam is an earthen dam located in Yasouj, in southwest of Iran. A significant hole and pipe have been observed in the corner of the right abutment from upstream view. The foundation is Marlstone, which has low cohesion and susceptible for internal erosion and piping in some conditions. Going through details of the design maps has shown that Lane’s criteria for selecting safe dimensions of the seepage control measures have not been considered properly. A series of the supportive walls are designed to attach to the right part of the spillway in order to increase the length of seepage. The pipe route of the erosion should also be grouted with high quality concrete.

Cementing is an essential part of every drilling operation. Protection of the wellbore from formation fluid invasion is one of the primary tasks of a cement job. Failure in this task results in catastrophic events, such as blow outs. Hence, in order to save the well and avoid risky and operationally difficult remedial cementing, slurry must be optimized to be resistant against gas migration phenomenon. In this paper, performances of the conventional slurries facing gas invasion were reviewed and compared with modified slurry containing special gas migration additive by using fluid migration analyzer device. The results of this study reveal the importance of proper additive utilization in slurry formulations. The rate of gas flow through the slurry in neat cement is very high; by using different types of additives, we observe obvious changes in the performance of the cement system. The rate of gas flow in neat class H cement was reported as 36000 ml/hr while the optimized cement formulation with anti-gas migration and thixotropic agents showed a gas flow rate of 13.8 ml/hr.

The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exponential distribution function has less effect on the tunnel stability compared to the two other distribution functions.

Among various practical measures used for restriction of the ground surface settlement in such tunnels driven in soft ground, selection of an appropriate excavation method plays a significant role. In this paper, employing suggested diagram by Yu & Chern, corresponding values of Niayesh tunnel has been inserted into the diagram. Later, two excavation methods namely: central diaphragm and side drift methods have been suggested and numerically modeled using Finite Difference Method. Side drift excavation pattern has finally been selected since it causes less settlement. To reach an optimized selection of excavation sequence through side drift method, seven excavation patterns have thus been recommended and numerically modeled. Results have revealed that the first pattern causes the least amount of settlement. Consequently, the aforementioned excavation pattern has finally been considered as an appropriate excavation pattern encompassing optimum excavation sequence for Niayesh tunnel.