Improved prediction of differential subsidence caused by underground mining

Observations in the field demonstrate that there exist discrepancies between the differential movements predicted from theory and those experienced in practice. From the point of view of structural damage, such discrepancies should be eliminated in order to decrease subsidence damage associated with mining. Using non-linear geometrical field theory, the deformation factors are modified and the limitation of linear elastic theory is established. Only when the rotation angles are smaller than 4 degrees is the application of conventional theory reasonable. A new deformation index, the mean rotation angle, is proposed. The study shows that there exists a relation between the mean rotation angle and the surface cracks. Incompatibility of rotation can initiate cracking. The outcome of the work presented will be helpful in improving the calculation accuracy of predicted differential movements, especially for steeper coal seam extraction, extraction under mountains, 'top coal caving' of thick seams, and mining in high relief areas. (C) 2000 Elsevier Science Ltd. All rights reserved.