非均质黏土隧道环向开挖面稳定性分析多限于圆形断面，而其他断面形状的破坏机制分析也很重要。为评价不同断面、埋深比、土体重度和抗剪强度沿深度线性增加的非均质强度等因素影响下黏土地层隧道环向开挖面稳定性，采用刚体平动运动单元上限有限元方法研究临界荷载比上限解和潜在破坏模式演化规律。结果表明：
同等高度条件下，直墙马蹄形隧道破坏极限状态对应的临界荷载比的上限解稍小于圆形隧道，椭圆形隧道对应的上限解随跨度增加而减小； 隧道破坏时的临界荷载比与土体非均质强度正相关而与土体重度负相关，其随埋深变化趋势受非均质强度和重度共同影响。运动单元上限有限元方法获得的非均质黏土地层隧道滑移线网破坏模式揭示，断面形状和埋深直接影响破坏范围，而其他因素的影响并不显著。临界荷载比的上限解与已有的离心机试验结果吻合较好，说明运动单元上限法及上限解拟合公式可作为非均质黏土地层隧道环向开挖面稳定性评价的有力手段及参考依据。
The research on
determining the stability of the circumferential excavation face of a tunnel in
the nonhomogeneous clay layers primarily focuses on circular cross-section
tunnels, and the action law of different cross-section
shapes has important significance. Therefore, the stability of the
circumferential excavation face of a tunnel in a clay layer is investigated as
a function of the factors influencing the stability, such as various cross-section shapes, buried depth ratios, soil weights, and heterogeneous
strength that increases linearly with depth. The upper limit finite element
method of rigid translational motion element is used to investigate the
relationship between the critical load ratio and potential failure mode. The
results show the following. (1) For the case of the same height of tunnel, the
critical load ratio under the failure limit state for the straight wall of the
horseshoeshaped tunnel is slightly lower than that of
the circular tunnel. However, the upper limit solution obtained for the elliptical
tunnel decreases with increasing span. The critical load ratio of tunnel
failure is positively related to the soil heterogeneous strength and negatively
correlated to the depth of soil. (2) The tunnel′s
buried depth is affected by the strength of soil heterogeneity and the soil
weight. Moreover, it is noted that failure range is determined by the shape of
cross-section and buried depth, and it is considerably
less sensitive to other factors from the failure mode of the sliding line
obtained using the upper limit finite element method. Therefore, the upper
limit solution with the critical load ratio agrees well with the centrifuge
test results. This demonstrates that the upper limit method of the moving
element and the fitting formula of the upper limit solution can be used to
evaluate the stability in the circumferential excavation face of tunnels in the
nonhomogeneous clay layer.
