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Abstract
Abstract. With the development of economy, land reclamation by dredger fill has become an effective measure to alleviate the shortage of land resources. However, the accompanying subsidence has always been a challenge to the safe use of soil in dredger fill area. In this study, Chongming East Shoal, China, where dredger filling activities are going on in recent years was selected as the study area. SBAS-InSAR was applied to monitor the variation of land subsidence and deformation in the recent two years. Furthermore, a total of 25 undisturbed soil samples including dredger fill and underlying soil were collected from 5 boreholes (maximum depth 55 m), and the land at each borehole had different a formation time. The physical properties and compressibility were tested by laboratory tests. Results show that for the current state, fast to slow subsidence velocity was observed in the reclamation area close to the coastline, which is controlled by building load and geological features of soil layers. The building load is the main factor affecting the land subsidence and special attention should be paid. It is the poor drainage condition of the soil layer in the offshore area resulting in slow subsidence. Consolidation degree and final settlement of soil can be obtained from monitoring data of land subsidence. Based on the settlement-time curve obtained by SBAS-InSAR, the estimated final settlement of typical settlement area is −27.03 to −38.96 mm, and the corresponding consolidation degree is 58.95 % on average. It still takes a long time to achieve stability. In conclusion, land subsidence is essentially the macro-accumulation of drainage consolidation of all the soil layers, so it is controlled by soil structure and engineering geological properties of both dredger fill and underlying soil layer. The research combined with field investigation, laboratory testing can provide a mechanism explanation for monitoring results. Future research will focus on longer monitoring time and a higher sampling frequency to enrich and improve the research.
Highlights
Shanghai is surrounded by many deep-water waterways
The dredger fills have a large amount of subsidence after land formation, and can produce land subsidence, which is considered a series of geological hazards (Haas and Ban, 2014) causing great economic losses (Galloway et al, 2000; Sarychikhina et al, 2011)
Using the Small Baseline Subset (SBAS)-InSAR method, we obtained the maps of mean deformation velocity in the period 22 January 2017– 20 October 2018 (Fig. 4)
Summary
Shanghai is surrounded by many deep-water waterways. A large amount of dredged waste soils combined with tense land resources makes that land reclamation became the best choice to treat waste soil and expand land. The Small Baseline Subset (SBAS) was proposed in the early 20th century (Berardino et al, 2002; Casu et al, 2006; Lanari et al, 2004). It is widely used in large-scale and long-time series surface deformation monitoring (Bing et al, 2016; Hu et al, 2014). Previous research on subsidence monitoring focused on the data processing algorithm for SAR data, rather than on the genetic mechanism in relation to reclamation activities and geological features
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