Abstract The river-crossing passage through Weisan Road of Nanjing will be built by shield tunneling, with two storeys, two-way four lanes and 14.5m diameter. The north exit approach mainly passes through muddy silt with rich water and low bearing capacity, and it is difficult to ensure the stability of soil and effective waterproofing by ordinary consolidation method. So it was designed to adopt artificial ground freezing. With the help of numerical method incorporating the site conditions, the effect of soil frost swelling on safety of diaphragm wall was studied, and the effect of local freezing and overall freezing on surface deformations was analyzed. In addition the reasonable thickness of freezing wall was studied. Research results showed that the diaphragm deformed a little due to large carrying capacity after the closure of freezing wall, the force bearing capacity of freezing wall and deformations were large after dismantling the sealing door on the wall and the distribution diagram of bending moments and displacements took the form of paraboloid at tunnel center. Compared with the overall freezing, local freezing could well control the freezing deformations and significantly reduce the surface heaving induced by freezing. When the thickness of freezing wall was 3.9m, the min.safety factor was 4.1 and max. deformation was 23.2mm. And when the thickness of freezing wall was 3 m, the min. safety factor was 3 and the max. deformation was 35.5mm. Taking the actual site conditions into consideration, the thickness of freezing wall of 3.9m is conservative and uneconomic and it is suggested that 3.0m should be taken.
Abstract：
The river-crossing passage through Weisan Road of Nanjing will be built by shield tunneling, with two storeys, two-way four lanes and 14.5m diameter. The north exit approach mainly passes through muddy silt with rich water and low bearing capacity, and it is difficult to ensure the stability of soil and effective waterproofing by ordinary consolidation method. So it was designed to adopt artificial ground freezing. With the help of numerical method incorporating the site conditions, the effect of soil frost swelling on safety of diaphragm wall was studied, and the effect of local freezing and overall freezing on surface deformations was analyzed. In addition the reasonable thickness of freezing wall was studied. Research results showed that the diaphragm deformed a little due to large carrying capacity after the closure of freezing wall, the force bearing capacity of freezing wall and deformations were large after dismantling the sealing door on the wall and the distribution diagram of bending moments and displacements took the form of paraboloid at tunnel center. Compared with the overall freezing, local freezing could well control the freezing deformations and significantly reduce the surface heaving induced by freezing. When the thickness of freezing wall was 3.9m, the min.safety factor was 4.1 and max. deformation was 23.2mm. And when the thickness of freezing wall was 3 m, the min. safety factor was 3 and the max. deformation was 35.5mm. Taking the actual site conditions into consideration, the thickness of freezing wall of 3.9m is conservative and uneconomic and it is suggested that 3.0m should be taken.
WEI Long-Hai,
Guo-Xiao-Hong,
Qiao-Chun-Jiang etc
.Study on Freezing Method Applied for Large Diameter River-crossing
Shield Tunnel in Nanjing City[J] MODERN TUNNELLING TECHNOLOGY, 2011,V48(3): 80-86
2011, Vol. 48 