不同顶管组合方式的管幕冻结温度场模型试验

Model test of freezing temperature field of the freeze-sealing pipe roof method under different pipe arrangements

拱北隧道作为港珠澳大桥珠海连接线的关键性工程,在国内外首次成功运用了管幕冻结技术。以此为背景,为更加全面地掌握饱和软土地层中管幕冻结温度场的分布特点,开展了不同顶管组合方式下的管幕冻结温度场模型试验研究。试验结果表明:各测点温度曲线在积极冻结期前4h急剧下降,随后逐渐减缓,降至砂土冰点后趋于平稳,三种布管方式均满足冻结设计要求;冻结管中低温盐水提供的冷量首先传递给顶管管壁,再以"面"的形式均匀地传递给周围土体;积极冻结21h后,采用四根空顶管组合的C区冻结壁竖向范围最大,空管管壁正上方冻结壁平均厚度约为105mm,在满足管幕刚度设计要求的前提下,可采此布管方式以达到快速形成冻结帷幕的目的。限位管开启后的4h内,实顶管中线垂直距离100mm范围内测点温度曲线虽有明显回升但仍维持在冻土冰点以下,超出此范围后温度变化影响逐渐减弱,且顶管间冻结壁稳定存在,表明限位管在满足管间有效封水的条件下,能在一定范围内起到定向限制地层冻胀的作用。优化后的双圆形冻结管在满足冻结设计要求的同时,更加便于安装且经济环保。

As the key project of the Zhuhai connecting line of the Hong Kong-Zhuhai-Macao Bridge,the Gongbei Tunnel successfully used the Freeze-Sealing Pipe Roof Method(FSPR)for the first time at home and abroad. Based on this background,a model test of FSPR under different pipe arrangements have carried out and the temperature field variation have been studied. The results show that during the active freezing period,the temperature of each measurement point decreased sharply in the first four hours,then slowed down gradually,and finally tended to be stable after falling to the sand freezing point. The three configurations of pipe arrangements all met the freezing design requirements. The freezing tube inside the hollow pipe first cooled the pipe wall and then reduced the temperature of the surrounding soil via the surface area of the pipe. After21 hours of active freezing,the vertical range of the frozen wall in Configuration C was the largest,and the average thickness of the frozen wall directly above the hollow pipe wall was about105 mm. On the premise of meeting the design requirements of the rigidity of the pipe roof,this configuration could be adopted to achieve the purpose of forming a frozen curtain quickly. The temperature curve of the measurement point within the vertical distance of100 mm at the concrete pipe middle line had a distinct rising stage in4 hours after the opening of the limitingtube,but it still remained below the freezing point and the frost wall between the pipes was stable. The existence of the frozen wall was stable,indicating that the limiting tube can limit the frost heave of the formation within a certain range under the condition that the water was effectively sealed between the pipes. The proposed optimized double circular freezing-tube can meet the requirements of freezing design,at the same time,it was more convenient to install,economical and environmentally friendly.