密实砂土地层盾构隧道开挖面失稳离心模型试验研究

砂土地层中盾构掘进时,开挖面支护力不足极易导致开挖面失稳事故。通过3种不同隧道埋深比（C/D=0.5,1和2）的离心模型试验对密实砂土地层中盾构隧道开挖面稳定性问题进行了研究。离心试验研究发现,随着开挖面位移的增大,开挖面支护力先减小为极限值而后逐渐增大并最终趋于残余值；开挖面前方土体总体呈现“楔形体+棱柱体”的失稳区；隧道相对浅埋时（如C/D=0.5）,极限状态下失稳区已扩展到地表；隧道相对深埋时（如C/D=1和2）,极限状态下失稳区尚处于地基内部；极限支护力随着隧道埋深比的增大先增加而后基本保持不变。最后,通过现有几种极限支护力理论计算模型对本文试验预测结果的比较分析,评估了上述理论方法的工程适用性。该研究成果对砂土地层中盾构开挖面稳定性控制具有指导意义。

Centrifugal model tests on face stability of shield tunnels in dense sand

When tunneling in sand using the shield machine, failure of the tunnel face occurs frequently due to the inadequate support pressure. Centrifugal model tests with different overburden-to-diameter ratios (i.e., C/D= 0.5, 1, 2) are performed to study the problem of tunnel face stability in dense sand. During the tunnel face failure, with the increase of the horizontal displacement of the tunnel face, it is found that the support pressure firstly decreases rapidly to the limit support pressure and then increases gradually to the residual support pressure. A “wedge-prism” failure zone occurs in front of the tunnel face after the face failure. For the relatively shallow buried tunnel (e.g. C/D=0.5), the failure zone has extended to the ground surface in the limit state. While for the relatively deep buried tunnel (e.g. C/D=1 and 2), the failure zone is still in the interior of the ground in the limit state. It is also found that the limit support pressure increases with the increase of relative depth C/Dand then remains almost the same. Finally, after comparing the limit support pressures obtained from the existing theoretical methods with those from the centrifugal model tests, the engineering applicability of the existing theoretical models is discussed. The results of this research may help to guarantee the face stability of the shield tunnels in sandy ground.