ABSTRACT:

In this paper, the practice of NATM (New Austrian Tunnelling Method) in Dongfeng tunnel in Suozhou-Huanghuagang railway is introduced in detail, including such aspects as reducing interference to surrounding rock as possible, controlling deformation and loosening of surrounding rock, adjusting support pattern and parameters on time etc.

I.
INTRODUCTION NATM

(New Austrian Tunnelling Method) was firstly put forward by professor L. V. Rabcewicz, an Austrian scholar, in 1950s. It was awarded patent right and formally named in 1963 after theoretical studies and project practice in several countries. Such as Austria, Swede and Italy etc. Then, NATM was quickly developed in underground engineering in Western Europe, Northern Europe, United States and Japan. The main points of NATM are:

  1. applying the theory of rock and soil mechanics,

  2. maintaining and utilizing self support capability of surrounding rock as a basic point.

  3. using bolt and shotcrete as main support means,

  4. controlling surrounding rock deformation and loosening.

  5. making surrounding rock as a part of tunnel support system and

  6. by means of monitoring to guide the design and construction of tunnels and underground engineering. Seven basic points were summed up in "The Guideline of NATM for Railway Tunnel" issued by China Railway Ministry.

2.
PROJECT DESCRIPTION

Dongfeng tunnel is a double-track railway tunnel. Its inlet and outlet mileages are DK45+683 and DK48+973. The total length of the tunnel is 3290m. It is one of the 4 longest runnels in Suozhou-Huanghuagang railway. The geological structure of the tunnel is very complicated. The tunnel was excavated in the Quaternary Period diluvial formation and marl. The maximum depth of the tunnel is 465m. The construction task with the mileage of DK45+683-DK47+660 (1977m) at the inlet section was taken by the 14th China Railway Construction Bureau. In this construction section there are 4 different kinds of surrounding rocks: scale 11, scale III, scale IV and scale V, according to China Railway Tunnel Surrounding Rock Classification Method. The scale II surrounding rock has poor stability and it is soft, broken seriously weathered there are, joints, and fissure growth. It is soften and mudded when water exists. In accordance with the requirements of NATM, different construction methods and technical measures were used during construction for different surrounding rock scales to realize safe, quality, economic and effective tunnelling.

3.
NEW PRACTICE OF NATM CONSTRUCTION
3.1
Scale IV and V surrounding rock section In general,

drilling and blasting method will be used for tunnel excavation in scale IV and V surrounding rock sections. In Dongfeng tunnel, excavation was also carried out by drilling and blasting method in scale IV and V surrounding rock sections, combined with smooth blasting method. But, in real operation, maintaining and utilizing self support capability of surrounding rock was taken as a basic point to reduce interference to surrounding rock as possible. The double excavation method of "advanced Central pilot, reserved smooth blasting layer and smooth blasting for enlargement" was firstly proposed. (1) Central pilot excavation According to the tunnel transverse section size.

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