Design and analysis of hole-forming technology for surface large diameter emergency rescue borehole

Surface large diameter borehole can be used as the escape channel for trapped people underground, and it is one of the important emergency rescue plans when mine accidents cause people trapped underground. However, the conventional large-diameter engineering hole is mainly formed by mud positive circulation and multi-stage reaming, which can not meet the rescue requirements. Focusing on the purpose of rescue and escape of large-diameter hole, this paper expounds the hole forming technology design principles including accurate connecting roadway, optimization of borehole structure, high-efficiency hole forming and safety connecting roadway. According to the specific construction conditions of overburden drilling, second foundation rock drilling, casing running and cementing, the paper analyzes the technologies of full casing drilling, pilot hole pipe-guide drilling, cluster DTH hammer reaming drilling, buoyancy casing running and interpolation cementing. Using the theory of loose zone and plastic zone of roadway surrounding rock to check the roof stability with considering that the rock mass in the plastic zone destroyed by the through tunnel drilling is a potential caving body. Then, the design and selection method of key parameters including safe through roadway distance and position are proposed, which could provide technical support for the construction of surface large diameter emergency rescue borehole.