Subsidence Rate Analyzing of Bangkok Soil Profile with InSAR Data

Abstract

The monitoring of land subsidence in Bangkok and its vicinity area has been conducted since 1978. The activities include the follow-up of the class one leveling survey technique as operated by the Royal Thai Survey Department (RTSD). The RTSD conducts surveying by using benchmarks in which the depressions or soil compression compartments at various depths located in the vicinity of the reference benchmarks. The data from these surveying techniques can serve as a substitute for calculating the amount of vertical movement to show the total subsidence of Bangkok and its vicinity area. However, the density of the observation points related to the coverage area was not dense enough to be used to indicate subsidence as an area consistent with the characteristics of the soil layer underground. This research presents a guideline for applying data from Time-Series InSAR technology. With the advantage of the technique, it can detect the rate of subsidence with the density of the observation points sufficient to display spatial relationships. We also propose a calculation method to estimate the subsidence rate of each soil layer at a deeper level by classifying the subsidence rate from the Time-Series InSAR data and dividing the data according to the type of depth of the foundation of the building. In Bangkok and its vicinity areas, we divide the depth of the foundation into three groups, which are the depths of 20, 40, and 80 meters. In this research, we study at the depth range of 20 meters to 40 meters. Finally, the final result of a vertical movementfrom our analysis with Time-Series InSAR data is 0.350 millimeters per year.