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.%南京纬三路过江通道在江中段采用盾构法修建,其内设上下层双向四车道,直径为14.5 m.该隧道江北盾构出洞时主要穿越淤泥质粘土,土体含水量大,承载力低,若采用普通加固方式很难保证盾构出洞破壁时土体的稳定和有效隔水,设计采用人工地层冻结加固技术.结合现场实际情况,利用数值方法,就冻结施工时土体冻胀效应对地下连续墙安全性的影响进行了研究,分析了局部冻结和全局冻结对地表变形的影响,探讨了冻结壁的合理厚度.研究结果表明:冻结壁交圈后,地下连续墙的受力较大、变形较小,井壁封门拆除后冻结壁受力和变形均较大,弯矩和位移分布图在隧道中心处呈抛物面形；与全局冻结方案相比,采用局部冻结法可以较好地控制冻结变形,显著降低冻结所造成的地表隆起量.当冻结壁厚度为3.9 m时,冻结壁的最小安全系数为4.1,最大变形为23.2 mm;当冻结壁厚度为3.0 m时,冻结壁的最小安全系数为3.0,最大变形为35.5 mm.考虑到现场实际情况,认为冻结壁厚度采用3.9 m较为保守,不经济,宜采用3.0 m.
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