Abstract

The Ca Pass Road tunnel is the new twin tunnel at the Ca Pass - a steep and dangerous mountain route in Vietnam using the new Austrian tunnelling method (NATM) - where the first time the twin tunnel was constructed in Viet Nam by drilling and blasting. The special issue in construction is the influence of the safety distance and blasting schemes to each tunnel. The blasting not only effected by impulse pressure but also induced the load transfer consequence to the adjacent tunnel. This paper presents a numerical modeling the effect of blasting interactions of twin tunnels during the construction stages as well the load-transfer mechanism between the two tunnels induced of detonations.

Introduction

In recent years, the demands for transportation have increased immensely in Vietnam urgently promoting infrastructure projects to improve the condition of the road system. The National Highway N01 is the backbone of the road system, connecting the North (from the China border) to the end South of the country. The Ca Road tunnel is the new 4200 m length twin-tube tunnel connection to replace the Ca Mountain Pass - a steep and dangerous mountain route in Vietnam. Which has a complex topography, steep slopes, and strong terrain dissection, deeply running close to the sea.

One of the biggest design issues that designer and constructor facing are the small distance between two NATM tunnel which parallel constructing procedure with the narrow spacing conditions, the blasting vibration effects during the construction of one tunnel may endanger the structure and normal operation of the existing tunnel that was excavated previously.

Thus, the drilling and blast construction work for small-spacing tunnels should be accurately designed under the guidance of effective detonation schemes. This is aimed at rendering the controllable destructive power of blasting vibration as well as guarantee both the safety of expected operation and the quality and progress of ongoing tunnel construction. Furthermore, it should be strictly observed and analyze parameters of excavation in real-time, ensuring the stability of its and the adjacent tunnel structure.

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