Model tests on influences of quasi-rectangular shield construction on underground pipelines

Excavation of quasi-rectangular shield tunnels causes uneven settlement of soils in pipelines, resulting in longitudinal deformation and failure of the pipelines. The indoor shrinkage model tests are conducted for the construction of quasi-rectangular shield tunnels. The influencing factors of the relative position of tunnels, buried depth of pipelines and soil loss rate are taken into account. The rules of subsidence, deformation of underground pipelines and surface settlement in dry sand are studied. The results reveal that the vertical displacement curve of the pipelines is Gaussian, the reverse bending point of the vertical displacement appears near the tunnel axis, the bending moment of the pipelines is “M” type distribution, and the maximum vertical displacement and bending moment are located directly above the tunnel axis. The impact of skew conditions of pipelines and tunnels is greater than that of their vertical conditions. The deeper the pipeline is, the larger the influence is. The vertical displacement of the pipelines decreases with the decrease of the soil loss rate. The vertical displacement of the pipelines directly above the tunnel axis and the maximum positive bending moment and two large negative bending moments of the pipelines decrease greatly, and the both sides of the pipelines are less affected. The surface settlement is directly affected by the soil loss, and the settlement value is larger than that of the underground pipelines.