邻近基坑施工作用下盾构隧道横向变形及开裂特性研究

Study on transverse deformation and cracking property of shield-driven tunnel induced by adjacent excavation

宁波地铁1号线某区间左线隧道在邻近基坑施工时产生较大位移和横向变形以及严重的管片结构开裂和破损现象。基于现场测试结果总结管片结构的破损特征,采用横向变形和开裂特性相互分离的数值方法探讨邻近基坑施工作用下隧道的横向变形和开裂特性,并预测管片环的开裂趋势。基于Plaxis的平面应变模型其收敛变形预测值小于测试值,坑内降水是导致该隧道产生较大刚体位移的重要原因。衬砌环"横椭圆"变形模式决定了其开裂范围,即拱顶和拱底附近为易开裂部位,相对最大裂缝宽度总出现在拱顶或拱底附近,这与现场观测结果一致。当竖向收敛增量达到1%隧道外径时,靠近基坑一侧的拱底宏观裂缝在管片厚度方向贯穿,成为贯穿裂缝。

The left shield tunnel between two stations of Ningbo metro line No.1 was damaged as a result of adjacent excavation. Cracks,concrete spalling and chipping appeared in the reinforced concrete segments due to the large displacement and transverse deformation of tunnel. The damage and cracking characteristics of this tunnel was summarized according to results of the on-site inspection and measurement. The transverse deformation and cracking property of shield tunnel induced by the adjacent excavation was numerically and separately studied,and the tendency of cracking was also numerically predicted. The numerical prediction of the vertical convergence was lower than the field data,and the rigid body displacement was mainly induced by the dewatering inside the excavation pit. The transverse deformation mode of tunnel lining ring,＂horizontal oval＂,actually determines its cracking range. The crown and invert of tunnel were the most vulnerable positions. The relative maximum crack width appeared around these positions. These predictions were agreed well with the field observations. The macro cracks at the invert of tunnel would run through the depth of reinforce concrete segment and become penetrating cracks if the increment of vertical convergence reached up to 1% tunnel external diameter.