Mine Subsidence is a phenomenon of lateral or vertical ground movement caused by a failure initiated at the mine level of man-made underground mines and an abandoned mine is a site where mining activities occurred but acceptable mine closure and reclamation did not take place or was incomplete. Subsidence is one of the major problems which is faced over an old abandoned mine. Presently there are limited means or methods which can predict subsidence over an old abandoned coal mine at a shallow depth efficiently and the precautionary methods that should be taken in these situations. This research paper will cover the possible causes which can lead to subsidence above an old abandoned board and pillar coal mines at a shallow depth. The research includes the calculation of the factor of safety for pillars and analysis of FoS using ANSYS and Monte Carlo Simulations for ascertaining subsidence. An old abandoned coal mine of South Eastern Coalfields Ltd. (SECL, a subsidiary of Coal India Limited), was considered for the study of coal pillar fatigue and eventual crushing of pillars over a long duration of time, simulation analysis of stress and strength of coal pillars over a long period, change in behavior of factor of safety as the dimension of the pillars changes.

The article describes the experimental studies on the recovery of chromite ore obtained from the Askale-Kop deposit (Erzurum/Turkey) using a laboratory-type KC-MD3 Knelson concentrator. For this purpose, the parameters of pulp feed rate, fluidization water flow rate, pulp solids ratio bowl speed and particle size were examined as variables in the experimental studies. As a result of the experiments, the maximum Cr2O3 grade was obtained at 54.68% in chromite concentrate at fluidization water flow rate of 12 l/min, pulp feed rate of 1.5 l/min, pulp solids ratio of 20% and bowl speed of 800 rpm. The highest concentrate recovery value (76.85%) was obtained at fluidization water flow rate of 6 l/min, pulp feed rate of 1.5 l/min, pulp solids ratio of 20% and bowl speed of 1080 rpm.

This study focuses on the influence of proppant parameters on the long-term conductivity of hydraulic fractures. Embedment of proppants in fracture walls and proppant crushing was studied using FCMS-V fracture conductivity system, field emission scanning electron microscope, polarization microscope and the screening analysis. The correlations between the conductivity, grain size, grain-size composition, proppant concentration and placement technique, closure pressure of fractures and proppant embedment were revealed. Embedment and crushing of proppant grains of different size under different fracture closure pressures were discussed. The recommendations on proppant placement during hydraulic fracturing were given as a case study of coalbed methane production in YC site of Ordos Basin in China.

The article presents the design model and results for the main crack development in closely spaced blasting in brittle rocks. The 3D modeling is described as case-study of crack formation in granite in perimeter blasting of ammonite charges at different spacing and filling of blastholes. The shapes and sizes are determined for the main cracks generated by blasting of single charge and three close-spaced charges. From the modeling results obtained for a specific charge, the method is proposed to determine efficient spacing of blastholes in perimeter blasting to ensure the maximal area of the created crack.

The new design of a powered roof support for the controlled longwall top coal caving in thick coal seams contains a special outlet and a reciprocating feeder. The introduction of such technology needs pre-testing and analysis of the outlet modes per the support units, such that to ensure the maximum allowable fill of the longwall conveyor without its overloading and dynamic phenomena. Created in Rocky DEM environment with that end in view, the simulation model takes into account the physical effect of rock mass fracture using the discrete element method, and enables variation in the design parameters and operating conditions of the powered roof support. The implemented experiments make it possible to assess the interdependence of the average velocity of coal outlet to the conveyor, the outlet gate angle and the feeder vibration frequency.

A brief description of coal resources in Transbaikalia is given. The issues of thermal and hydrochemical modification of coal from Apsat deposit are discussed. The usability of carbonization, gas–steam activation and alkaline treatment of low-caking coal for the improvement of coal adsorption capacity is determined. The proposed technology of Apsat coal preparation and dressing includes crushing, screening, carbonization and steam activation. The characteristics of the initial and treated coal are presented. The main physicochemical properties of the produced carbon adsorbents are determined. The coal modification parameters are identified. The computer-aided modeling of activated carbon adsorbents based on the quantum–chemical interaction of particles is described. The application areas of high-quality adsorbents in mining waste treatment are specified.

The influence of phase transitions in moist and salt-containing soil on freezing process is analyzed. The effects connected with the crystallization heat of pore water under negative temperatures and with the crystallization heat of salt when the eutectic point is reached are discussed. The conclusions on reachability of the eutectic point in artificially frozen strata above saline are drawn. Using a mathematical mode of heat processes in artificially frozen clay containing the common salt solution, the influence of the offset of the eutectic point on the temperature field in the frozen ground is analyzed.

By combining the advantages of InSAR, Probabilistic Integral Method and Genetic Algorithm, an improved method for dynamic prediction of probability integral parameters is proposed to realize subsidence inversion and prediction in insufficient mining. Firstly, InSAR is used to obtain the time series information of surface deformation in goaf. Then, a genetic algorithm-based parameter inversion model is constructed to invert the subsidence parameters such as subsidence coefficient and influence radius. After that, a dynamic prediction function is established to obtain the complete surface subsidence pattern and dynamic change trend of the mining area. Taking a goaf in Shanxi Province as the experimental object, Sentinel-1A(S-1A) image as the data source, combined with PIM and InSAR data, the parameter inversion model is used to successfully obtain the dynamic change process of mining subsidence parameters. The results show that the dynamic prediction function can achieve a certain effect on surface prediction in insufficient mining, and the parameter inversion model based on genetic algorithm has a high inversion accuracy, which provides a basis for surface prediction in insufficient mining.

In this study, the rebound hardness values (Shore–Schmidt–Leeb) were calculated for 12 different carbonate rocks using three different devices. The relationships between hardness values and rock cuttability properties (specific cutting energy and noise level) were investigated by simple and multiple regression analyses. It is determined that the Leeb hardness of the rocks can be an alternative to the Shore hardness and Schmidt hardness and that both the specific cutting energy and the noise level can be estimated with the Leeb hardness values.

A series of laboratory pull-out tests were performed on several types of bolts to investigate the effect of profile geometry of resin grouted bolts on load transfer mechanism. Therefore, three different types of bolts were used to prepare twelve series of specimens with different profiles. To evaluate the effect of bond length, the specimens were made using rebar bolts with two embedment lengths of 75 mm and 150 mm. The results showed that load transfer capacity and displacement at peak load were effectively related to the profile configuration and annulus thickness of resin. The bolt types T1 and G2 had higher peak share stress levels and the bolts with a rib spacing of 12.5, 16, 25 and 8 mm had the highest peak shear strength respectively. By decreasing the rib spacing and embedment length, the system stiffness increased. In the bolt types T1 and G2, by increasing the embedment length from 75 mm to 150 mm, the shear stress decreased by 7.8% and 10.5% and their stiffness decreased by 60.8% and 75.6% respectively. As the thickness of the resin annulus increased, the peak load decreased.