Experimental study and engineering application of jacking retractable concrete filled steel tubular column

To overcome the issue that exists in gob side entry retaining, a gob side entry retaining technology based on jacking retractable concrete filled steel tubular column was proposed. A new jacking retractable concrete filled steel tubular column structure and roadway retaining technology was developed. In order to verify the resistance increase and pressure relief performance of the column designed, the compressible bearing tests of different pressure relief structures were carried out. The results show that the stable bearing capacity of poplar in the shrinkable stage is 200 kN and the extreme bearing capacity is 700 kN. The stable bearing capacity of reinforced mesh column in the shrinkable stage is 400 kN and the extreme bearing capacity is 750 kN. Correspondingly, the stable bearing capacity of pine in the shrinkable stage is 500 kN and the extreme bearing capacity is 900 kN, the compression rate of pine is the highest, reaching 77.7%, indicating that pine is more suitable as pressure relief structure. Through the analysis of the bearing capacity test of the long and short columns, the high bearing capacity characteristics of jacking columns were verified, the reduction factor of slenderness ratio of the column bearing capacity was modified, and the calculation formula for the ultimate bearing capacity of the columns in compression stage and stability stage was obtained. By summarizing and analyzing various calculation methods, the calculation formulas of roadway side support resistance and reasonable compression in line with the technology of jacking retractable concrete filled steel tubular column were given. According to the project background in the retaining roadway along the goaf at the A02 working face in the 3rd lower section of Luxi Coal Mine, the resistance and compression of roadway side support were analyzed. Then, on the basis of the experiment, the bearing capacity and force analysis of the retaining roadway were carried out according to the pillar structure design. The results of engineering practice show that the support scheme of one row 299 mm×10 mm jacking retractable concrete filled steel tubular column and one column 21.6 mm×10 300 mm roof control anchor cable, combined with “wind curtain to isolate goaf + net spraying layer” meets the requirements of roadway stability. The support technology has the characteristics of good jacking effect in the initial stage, strong resistance increasing deformation capacity and high supporting force in the later stage. It has a good application prospect in the roadway retaining project where the basic roof settlement movement is violent, and the roadway retention effect will be better if it is further combined with the pressure relief of side cutting roof in goaf and the recovery and reuse of pillar shell steel pipes.