盾构施工引起地面长期沉降的理论计算研究

 对盾构施工引起的隧道轴线上方地面工后沉降进行研究，结果表明，土体开挖卸荷引起应力释放，产生初始超孔隙水压力，其分布呈三角形。假定衬砌不排水、土体为单面排水、压缩层厚度为隧道覆土厚度，采用太沙基一维固结理论，得到地面工后固结沉降的理论计算公式。假定地面长期沉降主要由施工期间沉降和工后固结沉降组成，进而得到地面长期沉降的理论计算公式。算例分析结果表明：该方法的预测值与实测值非常吻合；上海软土地区盾构隧道施工引起的地面长期沉降相当显著，最终地面沉降量在80 mm以上，固结沉降占总沉降量的80%～90%；按最小覆土深度5 m计算，需要2 a以上地面沉降才能最终稳定。

RESEARCH ON THEORETICAL CALCULATION OF LONG-TERM GROUND SETTLEMENT CAUSED BY SHIELD TUNNELING

Post-construction consolidation settlement of soil above tunnel axis caused by shield tunneling is studied. Initial excess pore water pressure，due to stress release by unloading of soil excavation，is triangle-shaped distributed. Assuming that linings are undrained，soil is under single-drainage condition，and thickness of compressed soil equals that of soil above tunnel；theoretical calculation formula of post-construction consolidation settlement is obtained based on Terzaghi’s one-dimensional consolidation theory. Long-term settlements of ground are divided into settlement during construction and post-construction consolidation settlement. Furthermore，theoretical calculation formula of long-term ground settlement is deduced. As shown in analytical calculation，the calculated results are in good agreement with the field data. It is analyzed that long-term ground settlements caused by shield tunneling construction in soft soil of Shanghai are very noticeable. Final settlements of ground can reach above 80 mm，and 80%～90% of settlements are consolidation settlement. Assuming that the earth thickness above the tunnel lining is 5 m，consolidation settlement will be stable after at least 2 years.