The forming law of sinking column in Huabei type coal field, especially at the Fengfeng coal mine is analyzed and the mechanism of groundwater inner cycle in sinking columns is put forth. The igneous intrusion and Mohorovicic discontinuity lift are considered as the main causes to generate abnormal geothermal to energize groundwater circulation and karst development in limestone. The CaCO3 dissolution accelerated by geothermal abnormality, by sub-critical and supercritical water is discussed. High content of CO2 generated by CaCO3decomposition and relieving when the skarn minerals form is considered to raise CO2 partial pressure and consequently enhance the dissolution of carbonate rocks. Chimney effect during hot water convection in the limestone aquifers was proposed. The paper assumes that the flame shaped cave in intensive convection areas developed into chimney that were favorable to convection. The overburden of the chimney collapsed and became sinking column. According to this, the causes that some sinking columns have permeable edge are explained. It is deduced that the above factors result in karst development with sinking column formation.
Inner circulation of groundwater