含黏粒砂土地层浅埋盾构隧道开挖渗流稳定性试验

针对含黏粒砂土地层浅埋盾构隧道开挖渗流稳定性问题,设计制作了主要由模型箱、水循环系统、盾构隧道与开挖面模型、饱和地层模型和量测系统组成的试验装置。通过模型试验,量测开挖面逐渐失稳过程中的地层沉降和开挖面饱和土压力以及前方地层孔隙水压力。结果表明:渗流条件下,开挖面前方地层孔隙水压力,会因地层黏-砂比的增大而增大,且会随开挖面体积损失的增大而增大;渗流会使开挖面极限有效土压力明显增大,开挖面极限有效土压力与地层黏-砂比基本上呈线性增加关系;地层极限失稳范围主要取决于开挖面前方和后方以及横向的破裂角,其中,后方破裂角受地层黏土含量和渗流的影响不大;无渗流时,地层极限失稳范围会因黏-砂比的增大而增大,而有渗流时,地层极限失稳范围会因黏-砂比的增大而减小。研究成果改进了对含黏粒砂土地层浅埋盾构隧道开挖渗流稳定性的认识,可以为实际工程以及有关的稳定性极限分析提供参考。

Experimental study on excavation-seepage stability for shallow shield tunnel in sandy ground with clay

In view of the stability of shallow shield tunnel excavation under seepage conditions in sandy ground with clay, a test equipment was designed and established, which mainly consists of model box, water circulation system, shield tunnel and excavation face model, saturated stratum model, and measurement system. Based on model tests, the ground settlement, saturated earth pressure, and pore water pressure in front of the tunnel were measured in the process of gradual instability of the tunnel face. Results show that under the seepage condition, the pore water pressure in front of the tunnel face increased with the increase of the clay content in soil and the volume loss of the tunnel face. Seepage could evidently increase the limit effective earth pressure at the tunnel face. The limit effective earth pressure increased linearly with the increase of clay-sand ratio. The limit collapse range of the soil was mainly dependent on the rupture angle in front and rear of the tunnel face and the transverse rupture angle, in which the rear rupture angle was not much affected by the clay content in soil and seepage. Under the condition of no seepage, the limit collapse range of the soil increased with the increase of clay-sand ratio, while under the condition of seepage, the limit collapse range of the soil decreased with the increase of clay-sand ratio. The research results improved the understanding of the stability of shallow shield tunnel excavation under seepage conditions in sandy ground with clay, which can provide reference for practical engineering and limit analysis of stability.