Abstract
This paper presents a methodology to exploit the Persistent Scatterer Interferometry (PSI) time series acquired by Sentinel-1 sensors for the detection and characterization of uplift phenomena in urban areas. The methodology has been applied to the Tower Hamlets Council area of London (United Kingdom) using Sentinel-1 data covering the period 2015–2017. The test area is a representative high-urbanized site affected by geohazards due to natural processes such as compaction of recent deposits, and also anthropogenic causes due to groundwater management and engineering works. The methodology has allowed the detection and characterization of a 5 km2 area recording average uplift rates of 7 mm/year and a maximum rate of 18 mm/year in the period May 2015–March 2017. Furthermore, the analysis of the Sentinel-1 time series highlights that starting from August 2016 uplift rates began to decrease. A comparison between the uplift rates and urban developments as well as geological, geotechnical, and hydrogeological factors suggests that the ground displacements occur in a particular geological context and are mainly attributed to the swelling of clayey soils. The detected uplift could be attributed to a transient effect of the groundwater rebound after completion of dewatering works for the recent underground constructions.
Highlights
Ground displacements can be evidence of several processes of natural origin such as swelling/shrinkage of expansive soils, compaction of recent deposits, tectonic displacements associated to the occurrence of earthquakes or long-term tectonic movements and anthropogenic causes such as pumping-induced aquifer-system compaction [1]
Two approaches have been implemented: (1) a statistical procedure to find the principal components (PC) of time series (TS) and (2) an automatic classification tool for TS based on statistical tests that analyze the variance
The analysis of the geotechnical parameters has highlighted a high value of swelling pressure for the clayey soils of the London Clay and Lambeth Group, and a low value for the alluvium soil and River Terrace Deposits present in the superficial deposits, confirming that bedrock formations, when wetted, have a great potential of volume change which can be responsible for the uplift
Summary
Ground displacements can be evidence of several processes of natural origin such as swelling/shrinkage of expansive soils, compaction of recent deposits, tectonic displacements associated to the occurrence of earthquakes or long-term tectonic movements and anthropogenic causes such as pumping-induced aquifer-system compaction [1]. Negative displacement corresponds to lowering of the earth surface named land subsidence positive displacement is the uplift of the earth surface. Uplift phenomena are less common and less studied than land subsidence. Positive movements (uplift) can occur as a result of various natural and human causes; for example, swelling of clay soils [3], fault effects [4], and water rebound in mining areas [5,6]. Uplift phenomena can lead to various environmental and engineering problems such as springs of polluted water [7] and damage to building foundations [8,9]
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