Course of the consolidation process of the subsoil made of coal sludges with varying permeability

The paper presents results of calculations of the course of the consolidation process of coal sludges subjected to the loading with consecutive heap layers made of coarse-grained colliery spoils. Geotechnical parameters of the sludges were assumed on the basis of the investigations carried out on the material from the sedimentation pond of the Coal Recovery Plant in Trachy. The colliery spoils were dumped in layers: the first layer -2 m thick, the second and the third one -4 meach, and the fourth -8m thick. The sludges deposited in the sedimentation pond were considered as a homogenous subsoil consolidating under the load applied on the surface. Taking into consideration the large surface of the pond (around 125 x 110 m) in relation to the thickness of the sludges (9 m ), the problem was considered as the consolidation at the uniaxial state of strain. The results of the calculations are depicted in the diagrams of settlement and the degree of consolidation versus time. Taking into consideration changes of the sludge permeability as the load increases was found to significantly improve the assessment of the actual course of consolidation. The increase of consolidation time with the diminishing permeability coefficient results in slower dissipation of the pore pressure and thus in slower increase of the effective stress. This issue is very important for the bearing capacity of the subsoil and the stability of the colliery spoils heap built on it