合理确定掌子面支护压力是保证隧道正常施工及周边环境安全的关键。为探究浅埋隧道中不同复合程度下复杂地层支护力上限值变化规律，基于三维有限单元极限分析软件Optum G3，建立一种考虑不同泥岩比例的浅埋隧道掌子面极限支护压力上限解模型，并通过案例对比分析验证模型的有效性。基于此，进一步探讨不同泥岩复合比例下掌子面支护压力上限解及对应失稳模式，并进行参数敏感性分析，拟合得到对应的简化计算公式。结果表明： 1）复合地层盾构隧道开挖过程中，泥岩比例低于50%时，掌子面支护力上限值增长平缓，大于该值后支护压力迅速上升； 2）复合地层掌子面破坏模式显著区别于均质土层，泥岩比例小于50%时，易失稳点出现在砂层与泥岩交界处，位置随泥岩比例的增加而上升，大于该值后出现在隧道中心位置并保持恒定； 3）极限支护压力上限解与隧道埋深比C/D、覆土内摩擦角φ及黏聚力c值呈正相关，且埋深比C/D越大，增长的幅度越大，当泥岩比例大于75%后，不同黏聚力下的极限支护力趋于接近。
The rational determination of tunnel face support
pressure is key to the normal construction of a tunnel and the safety of the
surrounding environment. To explore the variation law of the upper limit value
of shallow tunnel support pressure in different composite strata, an upper
limit solution model of the limit support pressure of shallow tunnel face
considering different proportions of mudstone is established based on threedimensional
finite element limit analysis software Optum G3, and the model′s effectiveness is verified using comparative analysis of cases.
Moreover, the upper limit solution and corresponding instability mode of tunnel
face support pressure under different mudstone proportions are discussed, and
the parameter sensitivity analysis is performed to obtain the corresponding
simplified calculation formula. The results show the following. (1) The upper
limit value of tunnel face support pressure increases more rapidly when the
proportion of mudstone is larger than 50% than when the proportion of mudstone
is less than 50%. (2) The tunnel face failure mode in composite strata
significantly differes from that in a homogeneous stratum. When the proportion
of mudstone is less than 50%, an instable point appears at the junction of sand
and mudstone, which increases with the proportion of mudstone; when the
proportion of mudstone is greater than 50%, an instable point appears at the
tunnel′s center axis. (3) The upper limit solution of
limit support pressure positively correlates with the ratio of tunnel buried
depth C/D, soil internal
friction angle φ, and cohesion value c; the larger the C/D, the greater the increase in the upper limit value of tunnel face
support pressure. When the proportion of mudstone is greater than 75%, the
limit support pressures under different cohesions are almost the same.
