Improved Knothe surface dynamic subsidence prediction model and its parameter analysis

In view of the shortcomings of the traditional Knothe time model in describing the process of surface dynamic subsidence, based on the Knothe time model, considering the nonlinear mechanical characteristics of the overlying strata, an improved Knothe time model is established. The theoretical analysis shows that the improved time model conforms to the variation laws of surface single point subsidence, subsidence velocity and subsidence acceleration. Based on the field measured data and the two-medium method, the expression for parameters of the improved Knothe time model is given. Based on the surface subsidence monitoring data of 4326 working face of Xinglongzhuang Coal Mine, 35101 working face of Sandaogou Coal Mine and 8403 fully mechanized working face of Yangquan No. 2 Coal Mine, the accuracies of the traditional Knothe time model and the improved Knothe time model are compared and analyzed. The results show that the improved time model can more truly reflect the dynamic change process of the surface with the mining time. The average relative standard deviation between the predicted and measured values is only 3.22%, which is far lower than 15.72% of the Knothe time model, which verifies the accuracy and reliability of the improved time model. The process of surface dynamic subsidence is affected by the mining speed v of coal seam, the thickness H_s of loose layer, the thickness H_j of bedrock layer and the full mining angle of loose layer φ_i and the full mining angle of bedrock φ_j, and the impact sensitivity is in the order of H_j, v, H_s, φ_j and φ_i. The results may provide some reference for the prediction of surface subsidence in coal seam mining.