Basing on Huolangyu tunnel, the authors use the finite software MADIS-GTS to analyze stress field, displacement field, and plastic zone distribution of the surrounding rock under tunnel entrance excavation. They also study stress distribution rules of unsymmetrical pressure section with backfilled soil. After a comparative analysis of the monitoring data, the authors define the key controlled zones of rock unsymmetrical deformation and stress concentration, they advise some effective measures to avoid partial tunnel destruction. Through monitoring the blasting vibration on key controlled zones, the authors analyze the correlation between blasting vibration effect and blasting condition, they put forward the blasting vibration control technology, such as stress improvement of surrounding rock, the multi-stage small wedge cutting holes, reasonable holes design, information-based construction, optimized blasting parameter. The methods will ensure the excavation safety in shallow buried tunnel under unsymmetrical pressure.

1 Introduction

Surrounding rock of highway tunnel entrance is unstable and mechanics complex due to the rock crushing, severe weathering and the shallow buried tunnel under unsymmetrical pressure. Adding to blasting load impact and repeated vibration effect, whole stability of surrounding rock is descended, the effect aggravate tunnel deformation and stress concentration. If the design has improper blasting parameter or shield parameter, tunnel landslide is likely to happen in tunnel excavation. Basing on Huolangyu tunnel in Mixing road reconstruction project, the authors define key controlled zones by comparing the finite software analysis to monitoring data. Through blasting vibration monitoring on key controlled zones, the authors put forward blasting vibration control technology, to ensure the excavation safety of the shallow buried tunnel under unsymmetrical pressure.

2 Project Overview

The total length of Huolangyu tunnel is 618 m, its design starting point is K10+215, terminal is K10+833, and tunnel headroom (width × high) is 10.5m × 5m. Site topography fluctuation is large, minimum level of tunnel entrance is 238.52 m, ridge top level is 297.21 m, the relative height is 58.7 m, it is the structural landform of denudation and low mountain. The surface of tunnel entrance is 2.5mClay-loam, underneath it is strong to medium weathering (biotite) inclined long shallow grain rock, joint fracture, rock core is short column to column, local fragmental, and so the comprehensive evaluation of surrounding rock is V level.

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