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This research work presents the rock mass characteristics and tunnel support system recommendations for hydroelectric power tunnels at Dasu dam site Pakistan. Two inverted U-shaped tunnels are proposed at the left bank of Indus river. The tunnels have inlet portals at an elevation of 773.00 m and outlet portals at an elevation of 758.00 m. The thickness of rock cover above the tunnels is between 100 and 200 m. Three types of rock are encountered at project site including Granulite, Amphibolite and Gabbronorite. Granulite rocks are encountered along the alignment of tunnels. Rock mass is classified using Rock mass rating (RMR) and Tunneling quality index (Q system). Support system is suggested based on values of Q and RMR. Correlation between Q-index and RMR is also derived. [ABSTRACT FROM AUTHOR]

Highlights • Abnormal stress conditions in unique sedimentary geological settings. • Presence of geological anomaly in rock burst zone. • Occurrence of frequent strain burst due to brittle failure of rock. • Occurrence of small scale fault slip burst due to the presence of shear zone. • Numerical evaluation of strain burst and fault slip burst in massive hard sedimentary rock. Abstract Tunneling in the Himalayas is full of surprises due to the active state of stresses, along with hostile geological and geomechanical heterogeneities. These sometimes go unnoticed during the design stage, which can result in rock burst type failures, which is the case with a recently completed hydroelectric project in Pakistan. In this project, twin headrace tunnels are excavated by tunnel boring machines (TBMs). Several rock bursts have occurred in the tunnels of the case study project, which are influenced by many factors like in-situ and excavation induced stresses, rock type and its brittleness, bedding orientation, geological anomalies, and geological structures. The Himalayas lay on the most active plate margin zone, and excavation here is more difficult than in the Andes, Alps, or any other mountain belt in the world. The project area is surrounded by the Main Boundary Thrust (MBT), the most active fault in the region, along with local faults that pass through the headrace tunnels. Due to this active stress condition, thrust faulting is common, and a complex structural geological regime is prevalent. Abnormal in-situ stress conditions at a deep depth have caused unique geological anomalies in the unique sedimentary geological settings of the project area. The TBM, which has little flexibility during excavation, has done little to disperse the in-situ stresses near the boundary of the tunnel and has exaggerated the situation. The two rock burst events of January 13, 2016, and May 31, 2015, are selected for this study; they are classified as strain and fault-slip bursts, respectively. Empirical approaches have been used to evaluate the proneness of rock burst occurrence. Numerical simulation has also predicted the actual failure zone well, in such deep excavation. The details documented for these events not only provide a basis for understanding the process of rock burst in the Himalayas but also provide a good reference regarding the occurrence of rock burst in deep civil tunnels excavated in the hard rock. [ABSTRACT FROM AUTHOR]

Sublevel stoping mining methods with delayed backfill are employed for mining steeply dipping ore deposits at deeper horizons. Cemented rockfill (CRF) is used as a backfilling material for open stopes formed during mining. In primary-secondary mining sequence, blast vibrations are induced in CRF during the extraction of adjacent stopes. Higher magnitude of blast vibrations may destabilize CRF causing failure and dilution of precious ore. This paper presents a methodology for calibrating a FLAC3D numerical model, encompassing mine backfill with blast-induced vibration data recorded from field instrumentation. Two FLAC3D models are prepared, one for simulating the blasting process and the other is prepared for backfill stability analysis. The first model resulted in load vectors to be applied to backfill and rock interface. The second model showed that the backfill fails under the blast vibrations induced by the adjacent production stope. The results of the back analysis of fill failure are presented and discussed. The methodology may serve as numerical model calibration procedure for mine backfill. [ABSTRACT FROM AUTHOR]

Sublevel stoping methods with delayed backfill are employed for mining tabular steeply dipping ore bodies. Cemented rockfill (CRF) is a type of backfill with simple operation, moderate capital cost while acquiring good strength. CRF stope is subjected to blast-induced vibrations during production blasting in adjacent stopes. Excessive dynamic load may destabilise backfill stope that leads to dilution of precious ore. Blast-induced vibrations can be monitored to assess the stability of CRF and to determine the blast waveforms for a detailed analysis using numerical models. This paper aims to establish that excessive blast-induced vibrations are the prime cause of backfill dilution at the case study mine. A detailed methodology and results of monitoring blast-induced vibrations in backfill are also presented. Blast vibrations are monitored in a CRF stope using three dimensional geophones and blast vibration monitors. The monitoring results obtained are processed and analysed to produce results in terms of velocity components and vector sum of velocity components. The data is further processed to examine particle velocity vs. scaled distances of individual blastholes and the effect of rock/backfill interface [ABSTRACT FROM AUTHOR]

Backfilling is one of the most critical tasks for sublevel stoping mining methods with delayed backfill. Selection of the type of backfill is a significant component of backfill design at preliminary stage of mine development. This paper presents a state-of-the-art review of backfill practices with focus on backfill operations in North America. Major difficulties and solutions in backfill practice have been laid down in this review. Preliminary recommendations are made for the case study mine based on the knowledge gained from the literature review andin situobservations. [ABSTRACT FROM PUBLISHER]

Blast vibrations are considered among the primary factors in destabilising cemented rockfill (CRF) stopes in open stoping systems with delayed backfill. This destabilisation occurs when the backfill face is subjected to blasting of an adjacent stope. Inadequate cementation, backfilling practices and blasting of adjacent stopes can be the causes of CRF failure and hence ore dilution. Poor blasting practices can cause greater blast vibrations and therefore can initiate fill failure. The magnitude of blast vibrations can be controlled by the powder factor and blast design. This study presents the effects of blast vibrations on CRF backfilled stopes. The effect of different blast loads and profiles are examined. Blast loads corresponding to non-ideal blasting are also simulated. [ABSTRACT FROM AUTHOR]

Thermal treatment followed by subsequent cooling conditions (slow and rapid) can induce damage to the rock surface and internal structure, which may lead to the instability and failure of the rock. The extent of the damage is measured by the damage factor (DT), which can be quantified in a laboratory by evaluating the changes in porosity, elastic modulus, ultrasonic velocities, acoustic emission signals, etc. However, the execution process for quantifying the damage factor necessitates laborious procedures and sophisticated equipment, which are time-consuming, costly, and may require technical expertise. Therefore, it is essential to quantify the extent of damage to the rock via alternate computer simulations. In this research, a new predictive model is proposed to quantify the damage factor. Three predictive models for quantifying the damage factors were developed based on multilinear regression (MLR), artificial neural networks (ANNs), and the adoptive neural-fuzzy inference system (ANFIS). The temperature (T), porosity (ρ), density (D), and P-waves were used as input variables in the development of predictive models for the damage factor. The performance of each predictive model was evaluated by the coefficient of determination (R2), the A20 index, the mean absolute percentage error (MAPE), the root mean square error (RMSE), and the variance accounted for (VAF). The comparative analysis of predictive models revealed that ANN models used for predicting the rock damage factor based on porosity in slow conditions give an R2 of 0.99, A20 index of 0.99, RMSE of 0.01, MAPE of 0.14, and a VAF of 100%, while rapid cooling gives an R2 of 0.99, A20 index of 0.99, RMSE of 0.02, MAPE of 0.36%, and a VAF of 99.99%. It has been proposed that an ANN-based predictive model is the most efficient model for quantifying the rock damage factor based on porosity compared to other models. The findings of this study will facilitate the rapid quantification of damage factors induced by thermal treatment and cooling conditions for effective and successful engineering project execution in high-temperature rock mechanics environments. [ABSTRACT FROM AUTHOR]

Diesel exhaust is a major cause of large number of occupational diseases. Acute and continuous exposure to DPM can cause numerous health issues including respiratory disease, lung disease, heart disease, etc. The NIOSH and the IARC consider DPM as 'probable carcinogenic' and 'carcinogenic', respectively. In large underground M/NM mines, DPM regulatory compliance is challenging. This paper primarily focuses on the evolution and application of real-time DPM monitoring in mining. This study discusses different monitors performance, their applications, and prospects of DPM monitoring in mining. This paper also presents an overview of core issues of using diesel equipment in underground mines and summarises existing DPM regulations in US and other countries. [ABSTRACT FROM AUTHOR]

Rockburst is an unstable failure of a rock mass which is influenced by many factors. During deep excavations, the presence of nearby geological structures such as minor faults, joints, and shear zones increases the likelihood of rockburst occurrence. A shear zone has been observed in the headrace tunnel in the Neelum Jhelum Hydropower Project, Pakistan, which has played an important role in major rockburst events in the project's history. A rockburst is a seismic event that involves the release of a great amount of energy as the dynamic wave radiated from the seismic source reaches the excavation boundary. In this paper, the FLAC 2D explicit numerical code has been used to simulate the dynamic phenomenon of rockburst near the shear zone in a headrace tunnel. The behavior of the rock mass around the tunnel has been studied under both static and dynamic loading. According to modeling results, rockburst significantly affected the upper left quadrant of the tunnel similar to the actual failure profile with a depth of approximately 5 m. The dynamic impact of rockburst has also affected the loading conditions of the support system in the adjacent tunnel. This study elucidates one of the most important rockburst controlling factors through numerical analysis and recommends yielding support measures that can withstand the dynamic impacts of rockburst in deep, hard rock tunnels. [ABSTRACT FROM AUTHOR]

Rockburst is a hazardous phenomenon in deep tunnels influenced by geological structural planes like faults, joints, and shear planes. Small-scale shear-plane-like structures have damaging impact on the boundaries of the tunnel, which act as barrier and accumulate high stresses. A shear plane combined with high stress conditions is very dangerous in deep excavations. Such a shear plane exposed in the side wall of the right headrace tunnel in the Neelum-Jehlum Hydropower Project. This project is constructed in the tectonically active Himalayas under high stress conditions. The influence of a shear zone on rockburst occurrence near the tunnel is studied. The FLAC3D explicit code simulated the shear zone in the right tunnel, revealing that the stresses are concentrated near the shear zone, while no such stress concentration is present in the left tunnel. The Rock mass got displaced near this shear zone. Modeling results confirm that the presence of shear zone in side wall of the right tunnel has a major influence on rockburst occurrence. A shear slip along this plane released huge amounts of accumulated energy, causing human fatalities and property damage. A comparison of numerical simulation with empirical rockburst criteria validates the actual conditions and help us to understand the phenomenon of stress concentration near the shear zone and its impact during deep tunneling. [ABSTRACT FROM AUTHOR]

Clay minerals are one of the most utilized minerals among non-metals. These are hydrous aluminum silicates with a layer (sheet-like) structure. Kaolin is a hydrous aluminosilicate mineral with a thin platelet structure. Kaolin is extensively used in paper, paint, and many other industries. Wet processing of kaolin will not be sustainable over the long term because global freshwater resources are becoming scarce. Hence, a process is necessary that does not consume water during the beneficiation of kaolin. This study developed a dry beneficiation process for low-grade kaolin of 59.6%, with 12% quartz and about 6% titaniferous impurities from Nagar Parkar, Sindh province, Pakistan. To develop a size difference between kaolinite and impurities, steel balls clad with rubber were used as the grinding media in a selective grinding unit. Screens of 60 and 400 mesh were employed to classify the feed of air classifier. Oversize +60 mesh was reground, 400 to 60 mesh fractions were sent to an air classifier, and −400 mesh was considered to be a product with the grade and recovery of 90.6% and 20.5%, respectively. Air classifier experiments were designed using central composite design. An experiment using a fan speed of 1200 revolutions per minute (rpm) and a shutter opening of 4.0 showed optimum results, with maximum kaolinite grade and recovery of 91.5% and 35.9%, respectively. The statistical models developed for grade and recovery predicted the optimum results at a fan speed of 1251 rpm and shutter opening of 3.3 with the maximum kaolinite grade and recovery of 91.1% and 24.7%, respectively. The differences between experimental and predicted grade and recovery were 0.1% and 2.4%, respectively. The characterization results showed the total upgrade of kaolin from 59.6% to 91.2%, with 27.1% recovery during the process. The designed methodology has the potential to improve the yield of the product by focusing on its recovery. Furthermore, the designed process can be improved by using different sized balls in the selective grinding unit. This beneficiation process can utilize more than one air classifier in series to achieve the targeted results. [ABSTRACT FROM AUTHOR]