Temporal changes of hydraulic properties of overburden aquifer induced by longwall mining in Ningtiaota coalfield, northwest China

Characterizing the mining induced temporal changes of hydraulic properties of the overburden aquifer is significant for groundwater resource protection. Conventional hydrogeological methods (e.g. hydraulic test, physical model test and numerical simulation) of determining hydraulic properties of the overburden aquifer cannot quantitatively analyze the temporal changes of the hydraulic properties induced by mining disturbances. This paper demonstrates a quantitative determination for the temporal changes of parameters (compressibility, porosity and specific storage) in the overburden aquifer influenced by the mining processes, based on in-situ continuous measurements of groundwater level that was affected by earth tide, atmospheric loading and mining disturbances. The results showed that, when working face reached a certain distance (127 m from borehole J6 in this study), those parameters (compressibility, porosity and specific storage) of overburden aquifer began to show gradual decrease, with approximately up to two order of magnitudes. After the working face passed by the observation borehole J6, those properties of overburden aquifer recovered in about 80 days, which might reflect the characteristic of elastic deformation of the aquifer. Those findings of the mining induced parameters' temporal changes could improve our understanding of the mining effects on aquifer system and could be meaningful in groundwater resource protection.