Study on quantitative evaluation method of hydrogeological structure and water-blocking capacity of coal seam floor

The structure in the Xinqiaocoalfield is well developed. Under the combined action of sedimentary environment，faults and large-scale fold structures, the Xinqiaocoalfield presents characteristics of blocks. There are differences in the relationship and other aspects, and its structural combination has become an important factor affecting the water-blocking ability of the floor water aquifer. Based on the above background, statistics of exploration drilling data in the well field, selection of typical borehole histograms, and a "three-layer" structure division method are proposed and used to divide the 2-2 coal floor water-proof layer within the well field into 4 types of structural models: a, b, c, d; from the qualitative evaluation of the four types of structural models from the damage types resisted by each interval in the "three-layer section" and the properties of its own rock formation, it is concluded that the water-blocking capacity from large to small is: a>b=d>c; Taking the 2301 working face as a typical working face, through the supplementary survey sampling and test analysis of the floor water aquifer layer, it is obtained that: layer Ⅲ (sandstone layer) has high rock mechanical strength; layer Ⅳ (silty mudstone layer) has extremely poor rock permeability.According to the comparative analysis of the field measurement results of the floor failure depth under mining conditions and the calculation results of the empirical formula, the III layer (sandstone layer) is determined as the key strata of mining failure resistance; and an evaluation model based on the type c structural model was established. The qualitative analysis determined the influence of the structure on the water-blocking capacity of the bottom water aquifer; finally, the weighted calculation of the mass ratio coefficient, the strength ratio coefficient and the thickness of the rock layer were carried out on the four types of structural models, the calculation results were analyzed and the advantages and disadvantages of the two calculation methods were compared. Based on the above analysis, the concept of the structural ratio coefficient comprehensively considering the thickness of the water barrier was initially proposed, which laid a theoretical foundation for further research on the quantitative evaluation method of water barrier capacity.