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Summary of Proposal LAN1058

TitleMonitoring of surface subsidence induced by metro tunneling
Investigator Dehghani, Maryam - K. N. Toosi University of technology, Faculty of Geodesy and Geomatics
Team Member
Dr Dehghani, Maryam - K. N. Toosi University of technology, Faculty of Geodesy and Geomatics Engineering,
Mr. Iravani, Alireza - K. N. Toosi University of Technology, Faculty of Civil Engineering
Dr Valadanzoej, Mohammad Javad - K. N. Toosi University of Technology, Faculty of Geodesy and Geomatics Engineering
Dr GhasemZadeh, Hassan - K. N. Toosi University of Technology, Faculty of Civil Engineering
SummaryObjectives:High subsidence rate especially in urban areas increases the risk of flooding and damages of their infrastructures due to the induced surface fracturing by subsidence. Therefore, in order to be able to better risk assessment and resource management, temporal and spatial monitoring of subsidence is required. GPS stations are not able to map the extent and pattern of the ground surface deformation caused by subsidence. Among various Geodetic and space-based techniques available, Interferometric SAR (InSAR) technique has shown its ability for measuring spatially continuous land subsidence. InSAR technique provides very precise measurements using highly correlated RADAR images. However, mid-resolution radar images such as ENVISAT ASAR are not able to detect and measure the local subsidence caused by human activities such as tunneling. These data can only be used to monitor the subsidence phenomena with a remarkable extent. Therefore, TerraSAR-x data with high spatial resolution allows us to monitor local subsidence with the small extent. A key factor to be mentioned is that TerraSAR-x can be applied in areas with low temporal decorrelation, since radar echo acquired at x-band are highly influenced by temporal decorrelation. Urban areas mainly consist of man-made structures such as buildings that are acting as corner reflectors. The corner reflectors with the persistent scattering behavior increase the TerraSAR-x capabilities in monitoring subsidence. We are going to monitor the subsidence caused by tunneling in metro constructions in Tehran, the capital city of Iran. The main purposes of the study are as follows: Phase 1: Radar Interferometry This phase consists of two other sub-phases as follows: 1.To detect the land subsidence in one of the metro stations using the radar interferometry. The extent and pattern of the deformation will be estimated. In this phase the risky areas in the vicinity of metro station will be identified. The results obtained in this part can serve as valuable information for constructions activities. 2.The subsidence rate can also be measured using the radar interferometry. The displacement map is the result of phase 1. 3.The obtained results are finally evaluated with the GPS and leveling data in the area. GPS and leveling measurements will be collected in the study area. Phase 2: Subsidence modeling A subsidence model will be generated using geology and geotechnical information. The model is then calibrated using the InSAR-derived displacement. The parameters to be calibrated are related to the soil mechanic properties such as internal friction angle and cohesion. The idea is that as we are not able to directly measure the modelís parameters precisely, the highly-precise interferometric measurements can be used to calibrate those parameters. Method: In phase 1 we are going to use DInSAR technique to detect and measure the subsidence rate. In this part TerraSAR-x data acquired at the Stripmap mode will be used. If the number of existing images in the archive is sufficient, we may be able to use time series analysis in order to study the temporal behavior of the subsidence (including short-term and long-term behaviors). In phase 2 we are going to use some specific models already defined by other scientists in order to model the subsidence. - Data requirements: The required data for this study is: 1.TerraSAR-x stripmap data 2. Large-scale topographic map (1:500) 3.Large-scale geology map 4.Soil mechanic map 5.Other geology and geo-technic information Deliverables: The outputs of the study are as follows: 1.The subsidence map (including location and deformation rate) 2.The evaluation results (InSAR with GPS and leveling) 3.The generated model with its calibration results The project output will be delivered through a complete report to DLR. This project is financially supported by K. N. Toosi University of Technology, Faculty of Civil Engineering.

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