ABSTRACT:

Korea has tunnels of approximately 1,843km in total length that are already completed or under constructions. The total number of tunnels in 1997 was 184 and reached to 932 in 2006, and it has increased by 750% for last 10 years. The number of tunnels longer than 500m was 52% of the total tunnels and 17% longer than 1,000m. Most tunnels were excavated in hard rock formation by drilling and blasting method. But, mechanized tunneling methods are widely adopted in Korea recently. There are difficult tunneling conditions in term of geotechnical conditions. This paper describes three special tunnelling projects which constructed in difficult geological conditions such as the 1,270m long riverbed subway tunnel constructed using a EPB-type shield TBM tunneling method, the 16.2km long loop railway tunnel located in a complex coal mining region with faults, cavities and coal measures, and the 4.6km long highway tunnel constructed by TBM-NATM combined method.

1. INTRODUCTION

Korea has tunnels of approximately 1,843km in total length that are already completed or under constructions. The number of tunnels in 1997 was 184 and reached to 932 in 2006, and it has rapidly increased by 750% for last 10 years. This paper describes three special tunnelling projects which constructed in difficult geological conditions such as the 845.5m long river-bed subway tunnel constructed using a EPB-type shield TBM tunnelling method, the 16.2km long loop railway tunnel located in a complex coal mining region with faults, cavities and coal measures, and the 4.6km long highway tunnel constructed by TBM-NATM combined method.

2. BUNDANG SUBWAY TUNNEL

The Bundang subway tunnel passing through the Han river-bed was constructed. Fig. 1 shows the longitudinal section of the site. The average rock cover is 23m and the total length of the tunnel is 1,270m. The contract amount is US$142 million. It took 18months for the completion of the tunnel

2.1. Geology

The tunnel mainly passed through metamorphic rock complex banded gneiss and mica schist. In the northern area of this site, a rock boundary of Jurassic Seoul granite intruded with gneiss exists. Special geological investigation such as directional core drilling, 3-D electrical resistivity survey and 3-D hydraulic fracturing experiment were performed. Fig. 2 shows the directional core drilling system.

Fig. 1. Longitudinal section of the site. (available in full paper)

Fig.2. Directional core drilling. (available in full paper)

The Directional core drilling is used to sample the sand and clay in the bedrock discontinuity. There is no lineation across the tunnel but a small scale tectonic line in northwestern direction exists. Based on the results of the geologic survey, the fractured zone was identified, and a detailed support pattern was designed.

2.2. Tunnel section

The length of ground section constructed by NATM is 380.5m and the length of the river-bed passing section constructed by an Earth Pressure Balanced (EPB) type shield TBM is 845.5m. Fig. 3 shows the earth pressure balance type shield TBM. The structures of tunnel include two ventilating openings and two shelter connection pits.

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