Research On The Construction Technology Of Tunnelling Under River By Slurry Shield Tunnel Boring Machine

The SS (Slurry Shield Machine ) method is the best choice for the tunnel projectwith the highest venture and challenge. In recent, four SS method projects have beencontracted, three biggest highway tunnels under Yangtze River(Wuhang, Nanjing,Shanghai) and a water transfusion tunnel through Yellow River,which transfusewater from south china to north china. The demands for construction technique of theSS method are in urgent, especially the problems in list: 1)Tunnel is constructed underthe very difficult geotectonic conditions, such as the sand layer with the water contentgreater than its liquid limit;under river with the overburden earth was less than 0.6times the tunnel diameter;the high water pressure;2)how to keep the building on thesurface safe, where the construction environment is complicated, e.g. many buildings,many pipelines, such as gas pipe, water supply and sewerage pipes, telephone andCATV cables;3)The special tunnel boring machine, which outer diameter of theshield is bigger than 10 m, the multi-diameter tunnel, The longest tunnel, which islonger than 1000 m.This paper presents a good example for SS method research——the "Li~Da"section, which is between "Lijiao station"～"Xiajiao station"～"Dashi station" inGuangzhou Metro line 3. By the case, this paper investigates the problems upward.According to the characters of the tunnel construction and the key techniques ofSS method, this paper discusses the problems upon. First, analysis on the geotectonicconditions of "Li~Da" section. The geotectonic conditions are very complicated,which contain high sensitivity soft mucky clay, sand layer filled with high pressurewater, and seriously (or moderately) weathered rocks;there are two sections underPearl River, one is 312 m, the other is 512 m. Second, designing of the SS based onthe conditions: 1.selection of cut-head and cutter, 2.the slurry dispose and circlesystem. Third, the construction technique: 1.the key of deep foundation pit for SSstarting in high sensitivity soft mucky clay;2.starting driven methods in the softground, 3.how to drive under the river, 4.how to overcome the collapse under the river,5.hoisting and moving TBM in whole. This paper contains first-hand data collectedfrom the worksite, all the information and conclusion methods came from thetechnique used in the project, which may be use to the SS method project in future.