Control of floor heave with rock bolts-steel piles coupling support technology

The uncontrolled floor heave in gob-side entry retaining is the serious problem of underground coal mining. This phenomenon has gravely restricted the application of pillarless mining that has been increasingly used in coal mines in recent years. This study proposes rock bolts-steel piles coupling support method to control severe floor heaves in gob-side entry retaining. This study employs finite element method to analyze stress-strain state in surrounding rocks around gob-side entry retaining. It was found that essential floor heave was caused by high horizontal stresses, which were transmitted from the sides of the entry, and vertical delamination of floor strata in the post-peak strains zone under the entry span. These processes complement each other and aggravate the floor heave. This paper proposes four floor reinforcement schemes. As a result of the study, the most effective floor reinforcement scheme was determined, which consists of 3 elements: steel piles installed in the corners of the entry, rock bolts installed between the piles and a steel belt that coupled the bolts in entry floor. The combination of the advantages of floor reinforcement with bolts and steel piles was the basis for the design of rock bolts-steel piles coupling technology. As a result, the post-peak strain and stress areas are the smallest, and floor heave reduces by 80%. Compared with other reinforcement methods, the advantages of rock bolts-steel piles coupling technology were successfully defined in controlling effect.