| Two separate single track tunnels are introduced to shielding section of Kecun station to Datang station on Guangzhou Metro line 3. The burying depth of the tunnel vertical section is 9.9-31.3m. The total length of drilling is 2967m. The space between two line s is 15.2-11.2m. There are 4 plane curved sections with a 1000m of radius of curve. The total length of curved sections occupies 54% of the line. The maximum grade of line in section is 3.0%. The minimum grade is 0.8%. The maximum length of grade is 365m. The buildings along the line are concentrated and underground pipeline is distributed complicated.The tunnel mainly passes through <7>strong weathered zone, <8>medium weathered zone and <9>weak weathered zone. Lithologic character is mud siltstone and conglomerate rock. Part of the tunnel passes through <5-l>plastic or slightly dense alluvium soil, <5-2>hard plastic or medium dense alluvium soil and <6>full weathered zone of rock. The medium weathered zone, strong weathered zone and alluvium are over the tunnel.The shielding section is designed as round tunnel with an outer diameter of 6.0m and a inner diameter of 5.4m. The thickness of segment is 300mm and the width is 1.5m. It divides into 6 pieces. Staggered joint assembly is adopted between rings. The concrete grade for segment is C50-S12.With full study to the engineering geological conditions, it is decided to use EPB Shield Machine for construction. The disc cutters of shield machine are designed with soft and hard arrangement. It can realize three kinds of drilling such as earth pressure balance, semi-open and full open. It has synchronous grouting system, segment erecting system and foam injecting system. The total thrust force of shield machine is 342 It and torque is 450t.m (the maximum torque 530t.m). 40T battery car and 17m3 ballast car shall be used for earth mucking and moving. One ring can be finished in only one operation. 40T gantry crane shall be provided at portal for vertical lifting.One set of shield machine is used for construction. It starts from right line. After entering into the tunnel by mining method via intermediate air shaft, it shall turn back on return line in tunnel at subsurface excavation section for construction of left line. Again entering into the tunnel by mining method via intermediate air shaft, it shall be disassembled in shielding shaft on left line and lifted out.During drilling, three modes of drilling shall be adopted respectively according to the conditions of stratum. According to the classification and features of surrounding rock, adaptive knives shall be selected and changed. Effective method shall be taken to improve the sediment soil. Relative technical measures shall be employed for starting drilling, initial drilling, normal drilling and arrival drilling of shield machine.Scientific and strict measurement control net for ground settlement shall be set up. Monitor and measurement shall be carried out regularly to master the effect to the ambience and tunnel itself during the construction and after completion of the tunnel. The monitor data from monitoring point in front of shield machine shall be analyzed in time and IT construction shall be performed in order to direct the shield drilling with monitored information. Bracket for change by pile foundation shall be adopted for buildings along the route. The way to strengthening monitor and pre-grouting shall be adopted for protection, follow-up grouting, construction measurement and suspension lifting shall be adopted for protection of underground pipeline.
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