Water-CO2 -rock interaction experiments to reveal the self-healing effect of fractured mining damaged rock

A series of physical or chemical reactions will happen between the damaged rock mass and underground water and gas after the underground coal mining. In the process,the water permeability of mining induced fracture will gradually be reduced which leads to the self-healing phenomenon of the water-conducted fracture. It is of great importance to study the self-healing mechanism on the scientific evaluation of ecological restoration of underground water and drawing up the water preserving mining method of fracture current-limiting. By conducting the water-CO2 -rock in- teraction experiments with acidic / alkaline water solution and fractured sandy mudstone samples,the self-healing mech- anisms and its development law are revealed under the effect of water swelling in clay mineral and filling and plugging of the secondary minerals or precipitate. The study results refer that the fractures in the rock sample have self-healing ability no matter when the rock in the acidic or alkaline water solution,and generally,the self-healing effect will be more significant while in the acidic water solution. In the self-healing process,the decline of permeability presents a partition characteristic of rapidly first and then slowly with time. The first rapid decline process is caused by the water swelling of clay mineral,and in the alkaline water solution condition the decline speed will be faster. Then,as time goes on,ions due to the dissolution or corrosion or rock minerals will react with the anion and cation and the free CO2 in the water solution. Furthermore,derived minerals such as Kaolinite and precipitate such as Fe(OH)3 will be genera- ted. These new materials adsorb and accumulate on the fracture face little by little,which lead to the decent of fracture permeability. Due to the low content of aluminosilicate minerals in the sandy mudstone samples,the increase input of CO2 in the acidic water solution may slow down the self-healing process of the fracture. Partial CO2 could not be deple- ted in the chemical process of WRI,the residual CO2 will dissolve and erode the rock minerals on the fracture surface in the form of carbonic acid. Then the fracture aperture will be enlarged,and the permeability may be increased.