Land subsidence monitoring in sinking coastal areas using distributed fiber optic sensing: a case study
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Land subsidence monitoring in sinking coastal areas using distributed fiber optic sensing: a case study Su‑Ping Liu1,2 · Bin Shi1 · Kai Gu1 · Cheng‑Cheng Zhang1 · Ji‑Long Yang3 · Song Zhang1 · Peng Yang1 Received: 6 April 2020 / Accepted: 13 June 2020 © Springer Nature B.V. 2020
Abstract A number of coastal areas have been suffering from severe land subsidence, which draws worldwide attention. Quantifying the subsidence and the contribution of each compacting stratum is crucial to study its development mechanism. In this paper, the distributed fiber optic sensing (DFOS) technique based on Brillouin scattering was adopted to monitor land subsidence in a 100-m-deep borehole located in Tianjin, China. Vertical strain profile was obtained by a kind of fixed-point cable embedded in the borehole, and the DFOS-based land subsidence system successfully achieved a 2-year-period in-situ investigation of the soft soil. The results revealed that the land subsidence rate was 21.6 mm/a after 2017, and the strata deformation measurements were refined up to each 5-m-thickness in vertical direction. The compression strata were localized at shallow strata (3.4–38.4 m), and the dominant contributors were soft soil strata at depth of 3.4 m to 18.4 m that the contribution of every 5 m thick stratum from top to bottom was 34.4%, 27% and 19.1%, respectively. The subsidence and strata contribution obtained by DFOS were in good agreement with those of extensometers. The groundwater fluctuations and additional loading may be the significant triggering factors of the compaction of the soft soil. This study showed that the DFOS-based measurement is an effective approach for land subsidence monitoring and will be a supplement to existing techniques in coastal areas. Keywords Land subsidence · Coastal areas · DFOS · Quantitative assessment · Tianjin
1 Introduction Coastal areas are among the most intensively used areas in the world, hosting evergrowing urban construction. There had been about 10% population around the world living in coastal areas by 2012 (Wang et al. 2012). With the expansion of human activities and the development of urban construction, some coastal cities have been suffering * Bin Shi [email protected] * Kai Gu [email protected] Extended author information available on the last page of the article
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Natural Hazards
from severe land subsidence, such as Shanghai and Tianjin (China), Jakarta (Indonesia), Ravenna (Italy), New Orleans (USA) and Tokyo (Japan) (Erkens et al. 2015; Shearer 1998; Wang et al. 2012). Ongoing land subsidence has become one of the greatest geological hazards to coastal cities, and even some cities increasingly sink rapidly than sea level rising (Erkens et al. 2015; Temmerman et al. 2013). To evaluate and control subsidence, the monitoring technologies of land subsidence developed rapidly over the past decades. Measurement techniques used commonly can be divided into two groups: space-based observation technique and ground-based survey technique, ranging from LiDAR and
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