Mechanism and impact of water seepage during shield tunnelling in sandy cobble strata: A case study

Sudden leaks often occur when constructing shield tunnels within saturated sandy cobble strata. Therefore, it is important to examine the reasons for water seepage and understand the mechanisms behind such problems. This paper presents a study that combines laser scanning technology with the Python programming language to create software for monitoring tunnel deformation. The software was employed in a practical subway tunnel scenario, successfully acquiring deformation data pertaining to the tunnel's structural segment through the analysis of point cloud data from the tunnel lining. Furthermore, the seepage-stress coupling theory was employed to establish a three-dimensional model of shield tunnel excavation, interlinking groundwater and stratigraphic factors with the sequence of shield tunnel excavation. The origins and mechanisms of water damage resulting from seepage and leakage are explicated through an examination of the seepage field, displacement field, and deformation of the tunnel structure pre- and post-excavation. Additionally, on-site monitoring data is considered. The mechanism of tunnel leakage is outlined as follows: Tunnel excavation completion induces alterations in the seepage field, leading to an accelerated inflow of groundwater into the soil beneath the tube sheet during shield excavation. The tube sheet of the shield tunnel, composed of sand and gravel layers, experiences vertical elliptical deformation that exacerbates shifts in the displacement field due to tunnel deformation's inception and progression. Excessive tube sheet deformation triggers fracture cracks, ultimately engendering the creation of seepage channels. These channels, in turn, foster seepage and water damage. The results of this paper provide a reference for preventing and remedying water infiltration and leakage in shield tunnels constructed of sandy cobble strata.