Deep hole drilling technology for final survey of a railway tunnel in Enshi， Hubei Province

Abstract:

To address the complex geological conditions in the deep boreholes of a railway tunnel survey in Enshi， Hubei， including karst cave development， severely fractured rock masses， and persistent fluid loss， a multi-diameter casing pipe reaming drilling technique combined with casing isolation technology is proposed as an effective solution for traversing the upper karst cave formations. This paper introduces the handling method for drilling tool falling （drill string runaway） accidents， analyzes the application effectiveness of conventional low-solid-phase flushing fluid， special flushing fluid for carbonaceous limestone sections， and fractured zone flushing fluid. In addition， it elaborates on the mechanism by which the polyvinyl alcohol （PVA） stabilizes borehole walls through adsorption， cementation， and film-forming. In the meantime， the primary causes leading to the abandonment of three boreholes are summarized. This establishes a technical paradigm for safe drilling in karst development zones for similar deep-hole drilling in railway tunnels.