1.School of Civil Engineering and Architecture,Anhui University of Science and Technology,Huainan ,China; 2.China Coal Mine Construction Group Co.,Ltd.,Hefei ,China

In order to solve the water inrush problem during the repair process of the damaged shaft of the auxiliary shaft in Banji coal mine,according to the actual damage of the shaft and the distribution law of aquifers in the stratum,and considering that the frozen wall would produce frost heaving during the formation process,in order to reduce the damage to the existing wellbore,it was proposed to use the control freezing technique with double-circle hole to seal the surrounding of the damaged wellbore.That is,the outer row of holes was frozen at full depth (673 m),and the inner row of holes was partially frozen in severely damaged formation (380 m and deeper).In order to effectively control the thickness of the frozen wall at each horizon to avoid the threat of frost heaving to the safety of the existing wellbore,according to the actual formation condition of frozen holes and the thermo-physical characteristics of the soil in each layer,during the freezing process,the measured data of the temperature measuring holes were used to predict the development of the frozen wall at various levels through numerical calculations,and the cooling capacity of some freezing holes was controlled based on the prediction results.In order to prevent the construction thermal disturbance from adversely affecting the stability of the frozen wall,in the process of wellbore cleaning and casting wall construction,the cooling supply was adjusted in time according to the development of the temperature field.It was known from the field test data that the overall temperature of the frozen formation above the depth of 380 m is about 5 ℃ higher than that of the stratum below the depth of 380 m.There is no water inrush phenomenon and the temperature of the frozen wall remained stable during the entire restoration process.It can be seen that the freezing control technology effectively limited the soil frost heaving,and the thickness of the frozen wall was relatively uniform,and the water sealing performance could meet design requirements,and the expected construction effect was achieved.This construction technology could provide an important reference for the development of similar projects in the future.