降水条件下基坑宽长比对邻近既有隧道变形的影响

Influence of Width-length Ratio of Foundation Pit on Deformation of Adjacent Existing Tunnel Under Dewatering Condition

针对基坑降水施工时对邻近既有隧道变形的影响已有学者进行研究,但降水条件下基坑宽度与长度的比值对隧道最大竖向位移的影响尚有空白。为探讨基坑降水时基坑宽长比对邻近隧道的变形影响,首先借助模型试验研究邻近隧道在基坑宽度和降水深度改变时产生的受力变形规律,再利用数值软件进一步分析基坑宽长比的影响,最后针对隧道竖向位移进行归一化处理,分析了不同降水深度影响下基坑宽长比对邻近既有隧道变形的影响规律。结果表明:通过模型试验可以发现,降水会使坑外出现明显的降水漏斗,并且随着基坑宽度和降水深度的增加,出水量会逐渐增加,坑内水位不断降低,既有隧道的竖向位移和弯矩产生明显变化,坑外隧道呈现压扁式的“横鸭蛋”变形。通过数值分析可以发现,当基坑宽长比较小时,应将宽长比和降水深度综合考虑,而当基坑宽长比较大时,应格外避免超降现象。另外,通过归一化发现,各降水深度下的位移曲线近似满足同一函数关系,当基坑宽长比小于0.4时,基坑宽度越大隧道位移越大;当基坑宽长比大于0.5时,隧道的竖向位移不会随着基坑宽度的增加而增大,但隧道位移的范围会增加4至5倍。

The influence of foundation pit dewatering construction on the deformation of adjacent existing tunnel has been studied by scholars,but the influence of width-length ratio of foundation pit on the maximum vertical displacement of tunnel under dewatering condition is still blank.In order to explore the influence of the width-length ratio of foundation pit on the deformation of adjacent tunnel during foundation pit dewatering,firstly,the stress and deformation rule of the adjacent tunnel is studied with the model test when the width of foundation pit and the depth of dewatering are changed.Then the influence of the width-length ratio of foundation pit is further analyzed with the numerical software.Finally,the vertical displacement of tunnel is normalized,and the influence of the width-length ratio of foundation pit on deformation of the adjacent existing tunnel under the influence of different dewatering depths is analyzed.The result shows that through the model test,it can be found that the causes obvious dewatering funnel outside the pit.With the increase of foundation pit width and depth,the amount of water increase gradually.The water level in the pit continues to decrease,and the vertical displacement and bending moment of the existing tunnel change significantly.The tunnel outside pit presents a deformation like‘flat horizontal duck egg’.Through numerical analysis,it can be found that when the width-to-length ratio of foundation pit is small,the width-to-length ratio and the dewatering depth should be considered comprehensively,while when the width-to-length ratio of the foundation pit is large,the phenomenon of over-drop should be particularly avoided.In addition,through normalization,it is found that the displacement curves at each dewatering depth approximately satisfy the same function relationship.When the width-to-length ratio of foundation pit is less than 0.4,the larger the width of foundation pit,the larger the displacement of tunnel.When the width-to-length ratio of foundation pit is greater than 0.5,the vertical displacement of tunnel will not increase with the increase of foundation pit width,but the range of tunnel displacement will increase by 4 to 5 times.