Sensitivity analysis of the effect of airflow velocity on the thermal comfort in underground mines

Displeasure in respect to air volumes and associated airflow velocities are well-documented complaints in underground mines. The complaints often differ in the form that there is too little airflow velocity or too much. In hot and humid climates such as those prevailing in many underground mines, convection heat transfer is the major mode of heat rejection from the human body, through the process of sweat evaporation. Consequently, the motion of the mine air plays a pivotal role in aiding this process. In this paper, a method was developed and adopted in the form of a “comfort model” to predict the optimum airflow velocity required to maintain heat comfort for the underground workforce at different activity levels (e.g. metabolic rates). Simulation analysis predicted comfort limits in the form of required sweat rate and maximum skin wetness. Tolerable worker heat exposure times were also predicted in order to minimize thermal strain due to dehydration. The results indicate that an airflow velocity in the range of 1 e2 m/s is the ideal velocity in order to provide a stress/strain free climate and also guarantee thermal comfort for the workers. Therefore, an optimal airflow velocity of 1.5 m/s for the miners' thermal comfort is suggested

A Laboratory Investigation of the Effect of Bedding Plane Inclination Angle on Hydro-Fracturing Breakdown Pressure in Stratified Rocks

In this paper, the effect of layer inclination, thickness and physical and mechanical properties of layers on hydraulic breakdown pressure was investigated. To achieve this aim, the model materials composed of kaolinite, cement and water in distinct ratios were used to simulate the laminated blocks like sandstone-shale and limestone-shale interbedded rocks. The fabricated rock blocks were drilled at different dip angles of 0⁰, 30⁰, 45⁰, 60⁰ and 90⁰ with respect to their bedding planes. The prepared laminated cylindrical samples are 54 mm in diameter and 108 mm in length. Then, these specimens were drilled in the center to prepare the hollow cylinder samples. The prepared specimens have two different layer thicknesses designated as low-thickness (t = 1cm) and high-thickness (t=2cm). The laboratory scaled hydraulic fracturing test was performed on thick-walled cylinder samples with different layer thicknesses and bedding plane inclination angles. The results of the study indicated the breakdown pressure is reduced for bedding plane angles ranging from 0⁰ to 45⁰ and increased for bedding plane angles 45⁰ to 90⁰. The minimum breakdown pressure occurred at inclination angle of 45◦. This phenomenon can be expressed as the anisotropy effect on the hydraulic fracturing breakdown pressure

Deformation and Failure Mechanism of a Collapse Induced by Underground Mining -- A Study of the Pusa Collapse in Guizhou Province of China

The rock structures at Pusa Village, located in the karst mountainous area of Nayong County, Guizhou Province, China are gently dipping. The upper part of this mountain is composed of hard rock layers while the lower section is made up of soft rocks which includes six (6) coal seams. Mining the coal seams excited the rest of the slope body leading to instability of the upper portions. On August 28, 2017, a massive landslide occurred in this area which resulted in the generation of 82, 500 cubic meters of debris. Significant casualties and social impacts were recorded. Twenty-six (26) fatalities and nine (9) missing people were reported. In this paper, the field engineering, geological conditions and long-term mining activity are investigated. A numerical model is developed to simulate and analyze the failure and deformation process of the Pusa collapse. The failure factors of the Pusa collapse can mainly be attributed to the unique geology of the slope rock mass, underground mining activities, topography and rainfall. The intensified mining activities increased the compressive stress in the upper layers and caused the development of fractures and cracks. The failure process of the Pusa collapse can be summarized into three stages, namely: (1) deformation of the roof layers, (2) cracking on the crest of the slope, (3) rapid deformation and collapse. The upper slope with high strength rocks developed crack—toppling failure while the lower slope with low strength rocks developed crack-slide failure. In summary, the slope deformation and failure mechanism are tensional, toppling, and shear failure