Discussion on twelve points of regulations regarding setting of waterproof coal (rock) pillars in coal mines

“Detailed Rules for Water Prevention and Control in Coal Mines” and “Code for the Setting of Coal Pillars and Coal Mining in Buildings, Water Bodies, Railways and Main Mines” are not only the cornerstone of coal mine water prevention and control work, but also the highest technical standards. Their authority comes from their scientific and rigorous nature. In order to maintain the authority of the regulations (norms) and better guide the retention of water resistant coal (rock) pillars in coal mines, twelve opinions on the provisions of Appendix 6 of “Detailed Rules” and Appendix 4 of “Three Down Mining Norms” are proposed for discussion: firstly, the meaning of the example diagram is vague, such as what is the standard for drawing auxiliary lines in Appendix 6-3c of “Detailed Rules” Due to the vague meaning, L₁ and L₂ have no solution, and the example diagram needs to be modified. Secondly, there is an error in the calculation formula, such as the incorrect formula in Appendix 6-5 of “Detailed Rules”, The formulas in Annex 6-8 of Detailed Rules are meaningless after deduction. The expression and attached diagram for the waterproof coal (rock) pillar with a filling water blocking zone at the top of the aquifer given in the “Three Bottom Mining Standards” are incorrect and need to be modified. The third issue is the omission of influencing factors, such as the “Detailed Rules” which did not take into account the movement angle of the overlying strata during mining when setting up water resistant coal (rock) columns for water drilling. Therefore, it is necessary to modify the example diagram and calculation formula. The fourth issue is that the reference standards are not unified. For example, formulas 6-6 and 6-8 in the “Detailed Rules” are both “borrowed” from the formula for sudden water coefficient, but the “borrowed” standards are not unified. It is recommended to unify the standards. Fifth, the parameters are not clear, such as the concept of “rock column” and the unit of water pressure in “λ is the ratio of water pressure to rock column width”, which results in the formula having no solution or being unable to apply; The object (water source) to be protected against water blocking coal (rock) pillars in adjacent mines is unclear, and the applicable conditions need to be clarified; The retention of water resistant coal (rock) pillars in adjacent mines bounded by faults is detached from reality due to the unclear “boundary” of the mine, and has become a simple problem of retaining water resistant coal (rock) pillars on faults. Sixth, the title summary is inappropriate, such as Appendix 6-2 and Appendix 6-3 of the Detailed Rules, which fail to grasp the essential difference of the problem; The main title of Appendix 6-3 contradicts the second subheading under its control (the main title is for water conducting faults, and the second subheading under the main title only applies to non water conducting faults) and should be corrected; The main title of Appendix 6-4 conflicts with the second subheading under its control (the main title is water conducting fault, and the subheading is non water conducting fault), and the title needs to be modified. The seventh issue is the confusion of the starting standards for the two ends of the waterproof coal (rock) pillar. Some are based on the intersection point between the coal seam floor and the fault plane, while others are based on the intersection point between the coal seam roof and the fault plane. This is not just a normative issue, but also related to whether the calculation formula is correct and has a solution. For example, the formula in Annex 6-4 of the Detailed Rules does not consider the thickness of the coal seam and needs to be revised. The eighth issue is the vague definition of the concept, such as whether the height of the water conducting fracture zone refers to the vertical height or the normal height being unclear. The calculation formula and accompanying drawings for the height of the water conducting fracture zone indicate that it includes urban collapse zones, which contradicts the explanation of the term (the water conducting fracture zone does not include collapse zones). It is recommended to further clarify the concept of the height of the water conducting fracture zone based on the dip angle of the coal seam, and clarify the difference between the height of the water conducting fracture zone and the height of the water conducting fracture zone. It is necessary to clarify whether the width of the waterproof coal (rock) pillar refers to the horizontal width or the inclined width. There are conceptual errors in the calculation of the water conducting fractured zone from the coal seam floor in Figure 6-8b of the Detailed Rules. The ninth is that the applicable conditions are vague, such as the retention of water-resistant coal (rock) pillars in the weathered zone of coal seam outcrops, and further clarification is needed on the applicable conditions for retaining coal pillars. Example figure 6-3c is only applicable to non water conducting faults and should be pre corrected. Ten is an error in the example diagram, as shown in Figure 6-7 of the Detailed Rules, which classify the roof waterproof coal (rock) pillar as a goaf. The endpoint of L_s length referred to in Figure 6-8a of the Detailed Rules is unknown and needs to be modified. Eleven is the lack of example diagrams, such as the omission of the example diagram of “water bearing faults” in Appendix 6-2 of “Detailed Rules”, which leads to unclear concepts of water bearing faults and requires the addition of example diagrams. Twelve is to focus on one aspect at the expense of another, as shown in Figure 6-8a of the “Detailed Rules”, which only considers the principle that mining one mine must not damage the adjacent mine’s waterproof coal (rock) pillars, but ignores the damage of mining one mine to the water conducting fault itself. It is necessary to modify the example diagram and add calculation formulas.