拱北隧道“钢管-冻土”复合结构承载力试验研究

Mechanical tests on bearing capacity of steel pipe-frozen soil composite structure applied in Gongbei Tunnel

管幕冻结法作为一种新型的隧道预支护工法,目前已被应用于港珠澳大桥珠海连接线拱北隧道施工中。管幕冻结法是利用顶管技术在隧道四周顶入大直径顶管,并利用冻结法将顶管之间的土体冻结起来,形成水密性的预支护结构。为了研究钢管-冻土复合结构在确保封水时的极限承载力和变形能力,以探求合理冻土温度,采用冻土单轴压缩试验机,对4种不同冻土温度进行钢管-冻土复合结构模型试验,并提出了封水条件下的极限状态判据,通过分析荷载-位移曲线,得到复合结构在封水条件下的极限承载力和变形能力。试验结果表明：温度较高时,冻土协调变形能力较好,但由于冻土本身强度较低,复合结构在封水条件下的极限承载力和变形能力较差;类似地,冻土温度较低时,强度较大,但由于冻土跟随钢管协调变形能力较差,在封水条件下的极限承载力和变形能力也较差;当温度适中时,冻土跟随钢管协调变形能力和冻土本身强度均处于相对理想状态,此时复合结构在封水条件下的极限承载力和变形能力相对较强,即在确保封水性能时所能承受变形的能力和极限荷载均较大。试验研究确定了该理想温度约为-10℃,该温度在拱北隧道管幕冻结实际施工中被采用,对类似工程施工具有一定的参考价值。

The freezing-sealing pipe roof（FSPR） as an innovative pre-supporting method in tunnel engineering has been applied to Gongbei Tunnel of Hong Kong-Zhuhai-Macao Bridge, which is the first application in the world. The definition of FSPR is that large-diameter steel pipes are laid out in a circle around the cross section of the tunnel in advance, and then the artificial ground freezing method is adopted to the freeze soil between steel pipes to form waterproof curtain. To study the bearing capacities of the steel pipe-frozen soil composite structure and the appropriate temperature of frozen soil between steel pipes in the actual project, the mechanical tests on steel pipe-frozen soil composite structure are conducted by using a uniaxial compression testing system of frozen soil with four different temperatures. The criterion for the ultimate deformation state of steel pipe-frozen soil composite structure under waterproofing is proposed. The bearing and deformation capacities of the composite structure under waterproofing are judged from the load-displacement curves in the tests. The results show that at relatively higher temperature, the deformation capacities of frozen soil following the steel pipes are better, but the bearing and deformation capacities of composite structure are relatively poor due to the low strength of frozen soil. Similarly, at relatively lower temperature, the results are relatively poor due to the poor plasticity of the frozen soil. When the temperature is moderate, the bearing and deformation capacities of composite structure are relatively strong, that is, the capability to withstand deformation and to bear the ultimate load is the largest. The ideal temperature of the frozen soil between steel pipes is about-10℃and it has been adopted in the actual construction of Gongbei Tunnel,which is of reference value for similar construction.