Laboratory testing of settlement propagation induced by pipe-roof pre-support deformation in sandy soils

A 'pipe-roof' is an increasingly popular supporting structure for underground space development. For efficient design and wider deployment, a thorough understanding of soil settlement propagation caused by deformations of the pipe-roof itself is critical. To this end, this paper describes a laboratory investigation into the interaction between pipe-roof deformation and surface settlement using a combination of fiber optic sensing, digital displacement gauges and soil imaging. The testing also explored the effects of pipe-roof stiffness and burial depth-span ratios on pipe-roof deformation and surface settlement. The results show that the development of pipe-roof deformation and surface settlement during excavation occur over three distinct stages. Increasing pipe-roof stiffness is also shown to effectively control the pipe-roof deformation and surface settlement but has a limited impact on the settlement trough. As the burial depth-span ratio increases, transmission of displacements from the pipe-roof deformation to surface settlement decreases significantly, this is due to soil arching effects above the pipe-roof, which becomes more significant as the burial depth-span ratio increases. The development of a three-dimensional surface settlement prediction model using Fourier transformation is described and predictions are shown to agree well with experimental data. The proposed design method is in a form amenable for use on routine projects in industry.