Analysis of Land Subsidence Characteristics in Embankment Area of Kosambi, Blanakan, and Wonosari

• Main Author: Yanto, Willy
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/43415
• Institution: Institut Teknologi Bandung

Land Subsidence is a periodic decrease in land surface or the sinking of the earth's surface which is characterized by the downward displacement of surface material due to movement under the surface of the earth. Subsidence is a global problem that can be caused by natural factors or human activities. Subsidence can be caused by natural compaction, loading or settlement, groundwater exploitation, tectonic factors such as plate movement and faults, as well as oil and gas extraction activities in sediment reservoir. The effect of each factor varies depending on human activity and natural phenomena in the area of subsidence. Natural compaction is the process which rock loses porosity due to natural phenomena and generally causes subsidence of about 0.1 to 1 centimeter per year. Tectonic activities such as fault movement generally cause subsidence of less than 1 millimeter because the depth of fault is far from the surface so the effect is quite small. Factors caused by human activity usually cause greater subsidence rate. The factor of building load on the ground can cause subsidence of up to 15 centimeters per year in the initial period of land consolidation which will continue to shrink depending on the condition of the land which is given the load. Exploitation of ground water and oil and gas can cause subsidence of up to 10 centimeters per year in the area around exploitation activities. Geologically, the northern coastline of Java consists of unconsolidated alluvial Holocene sediments which should have small subsidence rate. Naturally, embankment and agriculture areas on the north coast of Java will experience a decrease in land surface due to the nature of alluvial deposits and it is indicated that they should be more influenced by Natural Compaction which will have subsidence rate around 1-2 cm per year. However, we found out that there are areas with subsidence magnitudes ranging from 1-10 cm per year to around 14 cm per year at Blanakan and Morosari, in contrast to Kosambi which have a small subsidence value. The subsidence characteristics in these three regions are determined by calculating the mathematical model of each factor causing the subsidence which is then compared with the measurement data in the field. Subsidence can causes impacts such as damage to buildings, roads and other infrastructures. Subsidence can also cause drainage problems, and also the loss of soil resistance to disasters such as floods. Comprehensive information about the characteristics of land subsidence can be applied to several important planning and mitigation efforts, such as flood and seawater intrusion control, groundwater extraction, environmental conservation, infrastructure design and construction, and development planning.