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Land subsidence has been seen to have an effect in many countries, especially countries with areas of very soft soil. Settlement is generally found in high economic and developed locations and often depends on the increasing demand of humans for water. Namely, increased water consumption due to groundwater pumping results in an increase in settlement. All of these causes affect the changes in groundwater level. The government of Thailand has created rules to control groundwater consumption in order to solve subsidence and others problems. Changes in the water level directly affect soil settlement. This paper studies the land subsidence behavior by means of soil profiles obtained from Bangkok and the central area of Thailand, which are very similar, as a prototype soil model. The settlement behavior is examined through centrifuge tests performed after the water level drawdown due to water pumping. The groundwater level increases due to controlled pumping. Finally, the settlement results of the centrifuge tests are compared with the land subsidence characteristics of the Bangkok area. This research focuses on the testing methodology and soil settlement behavior. The land subsidence of Bangkok clay occurs continuously, but the vertical settlement of Kaolin clay is seen to be different at each stage of testing.

The Chao Phraya River basin is located in the central area of Thailand, which experiences many land subsidence issues due to groundwater pumping. The Department of Groundwater Resources (DGR) has been recording data on the changes in the groundwater level due to water pumping since 1960 until the present time. In 1997, the DGR issued a law regulating the use of groundwater due to its effect on the changes in the groundwater level. The changing of the groundwater level was separated into two periods. The first period is the high groundwater pumping ratio that led to a rapid decrease in the groundwater level of about 27 m from the ground surface. After the DGR issued the new law in the second period, the pumping ratio decreased and the groundwater level increased. The groundwater level tends to reach the ground surface. In the past, the groundwater level decrease was affected by the land subsidence. Therefore, this study focused on calculating and learning the behavior of the soil surface displacement during groundwater level recovery to the ground surface in Bangkok, Thailand. We obtained the 3D soil profiles adopted from eight boreholes from the Department of Public Works and Town & Country Planning. The soil profile data were verified by monitoring the data from the Department of Groundwater Resources (DGR) in the same area. The soil layers of the 3D soil profile were analyzed to calculate the soil surface displacement based on the consolidation theory of Terzaghi. We also examined the displacement behavior of the clay layers during the groundwater level recovery to the ground surface by assuming that the soil layers below the groundwater level do not settle or rebound. The surface displacement results showed that the surface ends to move upward or rebound, which is a similar trend to that reported in previous research. All the considered locations showed similar soil surface displacement trends. The soil displacement ratio is 0.21 to 0.53 cm/year during the groundwater recovery.

Chao Phraya River basin is located in the central area of Thailand which has a lot of ground displacement issues due to groundwater pumping. Following the Department of Groundwater Resources (DGR) in Thailand recording data, the groundwater level changed due to water pumping from 1960 until now. In 1997, DGR issued a law regulating the use of groundwater effect to the characteristic of changing groundwater levels. Therefore, the characteristic of groundwater level change was separated into two periods. In the first period, the high groundwater pumping rate led to a rapid decrease in groundwater level at about 27 meters from the ground surface. After DGR issued the law, the pumping ratio decreased and the groundwater level was increased or recovered close to the ground surface. The groundwater level recovery still affected ground displacement. This study focuses on evaluating and predicting ground displacement during groundwater level recovery in the future based on Terzaghi's theory. The study area considers only zone D (10 to 14 m of soft clay thickness) in the Bangkok clay area. The soil profile and the soil boring log were gathered from the Department of Public Works and Town & Country Planning in Thailand. This study research the ground displacement behavior of the clay layer during groundwater recovery. All data will be used to make a 3D soil profile and calculate to predict ground displacement in the future of the soil layer. The results found that the ground displacement has rebound to the ground surface of every bored hole during the groundwater recovery.