Abstract
Continuous pumping of groundwater will induce uneven ground settlement, which may adversely affect the nearby metro tunnels. In this paper, taking Nantong Metro Line 1 crossing Nantong Port Water Plant as an example, the surface level measurement and subsurface deformation monitoring using vertically distributed fiber-optic sensing are implemented to acquire the surface and subsurface settlement of emergency water supply conditions. The fiber-optic cable vertically buried in the constant-temperature layer is used to measure the subsurface strain field and deduce the deformation amount of each stratum. The monitoring results show that, during the pumping, the deformation of the aquifer and ground surface is linearly compressed with time; after the pumping, the ground surface continues to settle linearly at a slower rate for about 50 days, followed by a slow linear rebound, and the aquifer is logarithmically rebounded. In addition, deep pumping causes the deformation of the aquifers to be much greater than the surface settlement; the surface settlement lags behind the settlement of the aquifers by 1–2 months; the surface rebound recovery also exhibits a similar delay. Fitting models were derived to predict the maximum settlement and curvature radius of the site, which indicates that the adverse effects against the metro tunnel are not negligible once the continuous pumping exceeds 15 days. Those insights can be referred by the practitioners for the control of urban subsidence.
Highlights
Ground subsidence is a hazardous environmental geology issue which reduces stratum elevations and yields damage to buildings and infrastructure (Herrera-García et al., 2021; Pacheco-Martínez et al, 2013)
Given the monitoring scenario of land subsidence, the deformation field along the sensing optical cable caused by soil compression or rebound at depth h can be calculated in accordance with the measured strain, which yields: h2
In order to further study the influence of the groundwater barrier on the deformation connectivity of the strata, the subsurface deformation values acquired by distributed fiber-optic sensing (DFOS) were substituted into the space-time matrix B
Summary
Ground subsidence is a hazardous environmental geology issue which reduces stratum elevations and yields damage to buildings and infrastructure (Herrera-García et al., 2021; Pacheco-Martínez et al, 2013). Given the monitoring scenario of land subsidence, the deformation field along the sensing optical cable caused by soil compression or rebound at depth h can be calculated in accordance with the measured strain, which yields: h2. That using the DFOS for subsidence monitoring, the submatrix Bs of the space-time matrix B is usually extracted to characterize the local distribution of stratum deformation field, which yields: éεus ê ê. Where hi is the length of a certain measured micro-element section of the DFOS in the formation
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