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Protective water barrier pillars (PWBPs) are inter-mine barrier pillars. An adequate PWBP can protect active mine workings from the danger of inundation from adjoining inundated workings. This paper discusses a hydro-mechanical coupled numerical modeling approach for the design of PWBPs, considering different flow regimes. The coupled model considers the effect of seepage through the roof, pillar, and floor on the mechanical strength of the rock mass and vice-versa. A statistical model based on the extent of positive volumetric strain zones (ZoPVS, %) was formulated to assess the mechanical stability of the pillar. The model considers the pillar width, cover depth, strength, modulus of elasticity of coal and roof/floor, and the extraction ratio as the input parameters. Based on the results of numerical modeling-based parametric studies, statistical models were developed to estimate the seepage rate for assessing the hydraulic performance of the pillar. The seepage rate of water through a PWBP was estimated in terms of the cover depth of the seam, compressive and tensile strengths and modulus of elasticity of the pillar system, mean in-situ horizontal stress, pillar width, extraction ratio, and permeability of the rock mass. A ZoPVS of 95% represented unstable behavior and piping failure of the pillar. The maximum seepage rate of 315 L/s/km (5000 GPM/km) was reckoned as the acceptable hydraulic performance of the PWBP based on the field experience in Indian geo-mining conditions. The validation of the model for two case studies with minimum pillar widths of 30–60 m at a cover depth of 84.5–134.5 m was in agreement with the field experiences. [ABSTRACT FROM AUTHOR]

Issues with conventional depillaring techniques resulted in unscientific development of a number of coal seams into rectangular/square shaped pillars, mainly, located at shallow depths in different coalfields of India. Continuous miner based mechanised depillaring (MD) has been introduced to extract these coal pillars which is the main stage of production. The practise of leaving a proper sized rib/snook is a legal requirement as it decides the efficiency and safety of the MD operation. However, MD of square/rectangular shaped pillars created irregular-shaped-heightened-rib/snook. Conventional empirical formula is not capable to estimate strength of such ribs/snooks. These ribs/snooks should be of sufficient size to protect the adjacent slicing operation and junction as well as it should fail in a controlled manner when shifted inside the goaf. Field studies conducted at 39 panels of 7 different mines found a number of factors affecting the design of rib/snook. Proper assessment of performance of different sizes and shapes of ribs/snooks in field is difficult due to the complex and challenging underground mining environment of depillaring. These challenges prohibit a detailed study to be carried out in field. Therefore, parametric study on calibrated numerical model is conducted to estimate the strength of rib/snook with variation in sizes and heights of rib/snook and depth of cover. Further, an empirical relationship is developed to estimate the strength of rib/snook based on multivariate regression analysis. The values of strength estimated by the developed relationship is found to be least when compared with the popular pillar strength formulations due to effect of pillar/rib/snook spalling observed during field investigation with increase in depth of working. Results of field and simulation studies are presented and discussed in this paper for the design of irregular-shaped-heightened-rib/snook. [ABSTRACT FROM AUTHOR]