Study on fracture zone of cross fault group in large section rectangular roadway under mining conditions

Dynamic stress could cause safety issues for rectangular roadway when passing through facture zones of fault groups. The stability of roadways could also be affected under mining conditions. This paper presents a case study of a fracture zone of cross fault group on No.4310 working face of Changping Mine. The relationship between mine pressure and positive stress on the upper plate of normal fault was analyzed based on the stress analysis of faults. The theory of ultra-low friction effect on rock mass and the theory of dynamic stress wave were applied to explore the effects of dynamic stress on fault fracture zone. Then the safety measures when roadway passes through faults zone were recommended. The authors demonstrated that the stress concentration caused by the interaction between the stresses of normal fault upper plate acting on the lower plate and the mine pressure could lead to multiple expansions of the fracture zone. The dynamic stress can destabilize rocks of fracture zone and damage plastic zones. The pre-grouting method could be used to improve the lithology of fault fracture zones. Using this approach, the roadway passed through the normal fault fracture zones in the form of a dinting so that the stress applied to break surrounding rocks was lower and the fracture zone that roadway passed through was smaller. Another measure was to apply reinforced support wherever fracture was developed. The reinforced support combined active and passive supports, and applied grouting and anchoring belt and metal support to cushion the load and consolidate the strength of surrounding rocks. The ranges of the reinforced support for the three faults in the bed plate tunnel are 40, 40,50 m, respectively,and the mining roadway needed to be support when the fracture was developed.