Evolution and coupling of “seepage field and chemical field” under regional grouting disturbance

In Huaibei coalfield, the technology of ground directional drilling and high-pressure grouting is widely used to control the karst water disaster of coal measures floor. After grouting, the filling and drainage path of the seepage field changes, and the grouting high pressure and the slurry water will change the distribution characteristics of the groundwater seepage field and chemical field of the injected target aquifer in a certain period of time. Taking Taoyuan Coal Mine in Huaibei Coalfield as the research object, the evolution model of seepage field and chemical field (referred to as “double field”) of the target layer under regional grouting disturbance is built by using the software of Feflow, the coupling mechanism of “double field” is discussed, and the Cl− which is less affected by the environment is selected as the simulation factor, and the analysis of the factors affecting solute transport under the “double field” coupling effect is carried out. On this basis, the mathematical model of solute diffusion under regional grouting disturbance is constructed. The results show that in the seepage field model after identification and verification, 71.9% of the points where the error between the simulated water level and the measured water level is less than 3m, and the simulation effect is good; Among the identified and verified chemical field models, the simulation effect of solute transport in mining area II4 is good, and the simulation value in mining area II1 is about 14.4 mg/L lower, with an error of about 6.6% of the actual value, less than 10%. The overall simulation effect is good. The Cl− in mining area II4 and II2 with relatively high permeability coefficient is easy to migrate and diffuse, while the rock in mining area II1 with low permeability coefficient is dense and has poor permeability. During the 50 years of model operation, it basically exists in the state of “stagnant water”. Based on the evolution characteristics of local seepage field in II4 mining area under grouting disturbance, it is considered that solute transport is mainly controlled by permeability coefficient, dispersion, hydraulic gradient, seepage velocity, grouting time, slurry specific gravity and other parameters. It is found that the concentration of Cl− reaches a peak within 18−22 years after the completion of grouting, and then begins to decrease, and reaching the equilibrium state before regional grouting approximately 40 years later. Based on the data obtained from multiple parameter setting operations, a mathematical model of solute diffusion under the “double field” coupling is established. The data with error rate less than 10% accounts for 81.4%, which indicates that the established mathematical model of solute diffusion is basically reliable. This study can provide scientific basis for the study of the water environment evolution of the injected target aquifer under the regional grouting disturbance and the prediction and early warning of coal mine water disasters, and has important theoretical and practical significance

Prediction of the Water Inrush Risk from an Overlying Separation Layer in the Thick Overburden of a Thick Coal Seam

With the expansion of coal mining westward in China, water inrush from seam roofs has become a prominent safety problem during mining. The roof rock of the coal seam in the Shilawusu coal mine has the characteristics of a double-layer structure, and the overlying separation space formed in the mining process of the coal seam poses a risk of water inrush. To ensure the safety of coal mine production, considering the geological and hydrogeological data of the mining area, the core recovery rate, lithologic assemblage index, key aquifer thickness, hydrostatic head and lithologic structure index of the Zhidan Formation are selected as evaluation indexes. The index weights are calculated based on the attribute hierarchical model and coefficient of variation methods, and subjective and objective preference coefficients are introduced to determine the ranking of comprehensive indexes. The catastrophe progression method is improved, and a zoning prediction model for water inrush risk is established by the improved catastrophe progression method. The results show that only a tiny part of the mining area is in danger, and most areas are in the safe and transition zones. The model realizes the prediction of the risk of water inrush from the overlying separation layer in the study area and provides a theoretical basis for the prevention and control of water inrush from the overlying separation layer in coal mining

Max-min fair allocation for resources with hybrid divisibilities

Resource allocation is a classic problem in economics and computer science. The application scenarios of resource allocation include inheritance settlements, computation resource sharing and so on. This paper focuses on the max-min fair allocation of resources in which m resources need to be allocated to n agents while maximizing the minimum utility of any agent. When money transfer is not allowed, the existing work on max-min fair allocation only focuses on the fair allocation of indivisible resources. However, in real applications, the allocated resource set may simultaneously include indivisible resources and divisible resources, e.g., the allocated resources in distributed systems include the indivisible CPU resources, the divisible storage resource and the divisible bandwidth resource. The combination of indivisible resources and divisible resources creates a new challenge and requires us to consider how to coordinate the allocations of indivisible resources and divisible resources in the allocation process. Therefore, we investigate the combined max-min fair allocation problem in which the allocated resource set consists of both indivisible resources and divisible resources. We present a 6+2 (ε > 0)-factor approximation algorithm for the restricted case where uij ∈ {0, uj} (i.e., the utility of a resource j is either 0 or uj for each agent i) and the agent valuations for the divisible resources are in proximity to each other. Moreover, we propose an approximation algorithm for the general case based on the augmented flow idea. Experiments conducted on real data show that the average performance of the proposed approximation algorithm is better than 80% of the performance of the optimal algorithm, which requires exponential time in the worst case unless P = NP. To the best of our knowledge, the proposed algorithm is the first approximation algorithm for the general case of the combined max-min fair allocation problem when money transfer is not allowed. The proposed algorithm can be adopted to design more efficient expert systems that apply to resource allocation in distributed systems, inheritance settlements and so on. The adoption of the proposed algorithm contributes to promoting the broader application of expert systems in the fair allocation of computation resources and social resources. The experimental results show that the proposed algorithm can perform well in real applications.The work was supported in part by the National Natural Science Foundation of China (61472079, 61170164, 61806053, 61807008), and the Natural Science Foundation of Jiangsu Province of China (BK20171363, BK20180356, BK20180369)