ABSTRACT:

Taking the construction of Wangfujing-Dongdan tunnel project of Beijing subway's Fuxingmen-Bawangfen line as an for example, the authors stated the construction technique of multi-tunneling at shallow depth under condition of friable and watery strata, studied and analyzed construction effects with three dimensional FEM theory, optimized the construction technique of multi-tunneling system, solved a series of problems in the construction, and therefore the project has achieved fair effect.

1.
FOREWORD

With a total length of 518.395 meters, the Wangfujing-Dongdan tunnel project of Beijing subway's Fuxingmen-Bawangfen line is located under the East Chang An Avenue which is featured by busy traffic and complicated underground pipelines. It is a multi-tunneling project with a very complicated environment. With tough geological and hydrologic conditions, the project is constructed by tunneling with shallow depth method, therefore, the project brings high construction difficulty and risk. According to three dimensional FEM, we simulated, verified and optimized the construction methods and schemes at different sections and under different geological conditions, chose reasonable construction methods and summed up a set of unprecedented subway construction techniques not only at home but also abroad. The technique includes drilling and support technique of super large section, construction technique of multi-tunneling at shallow depth under condition or friable and watery strata, construction technique at turning points of complicated section, study of construction effects, monitoring and measuring techniques. etc..

2.
A BRIEFING OF THE PROJECT

2. 1 Structural type This part is a two-line turning back part with 2 transition lines, 1 spare line, 2 communication passages, a ventilation duet, outflanking tunnels and separation doors. The tunnel has 10 sections and 36 section turning points. It is the subway interval currently in China with the most complete functions, the soil excavation quantity reaches 80,000 m3, and concrete usage reaches 43,000 m3. The tunnel goes with a frequent change of sections, the biggest section is 14.2mxI0.678m(width × height). 2.2 Engineering Geology and Hydrology The interval is located at the middle and lower reaches of spine of Yong Ding River's alluvial fan, belongs to Quaternary Period stratum. The surface is asphalt concrete and artificial mixed filled soil, and then the successive layers are light mild clay, middle fine sandy clay, gravel, mild clay, sand and clay. (see figure 2) The multi-tunnels go through the mixed layer of clay, sand and gravel. soil collapse is easy to happen during excavation due to [he poor self-stability of surrounding soil and vibration caused by the ground dynamic load. The area has a rich deposit of underground water.. Frorn top to bottom, there are upper stagnant water, phreatic water and bearing water. Influenced by seasonal precipitation and pipeline permeation. upper stagnant water varies greatly: phreatic water's depth is 12.4–16.2 m. permeation coefficient is 100m- 120m/d; bearing water's depth is 15.7~20.4m. permeation coefficient is 150–180m/d, the work's base slab is positioned in bearing water. 2.3 Geographic Environment of Surroundings The project is located at East Chang An Avenue, a busy street with heavy traffic and tall buildings aside. Underground pipelines.

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