Estimation of Settlement Induced Land Subsidence of Marine Clay on Kamal Muara Area, Northern Jakarta, Based on the Change of Pore Water Pressure

Land subsidence phenomena which occurred in last 30 years in Jakarta affected by groundwater extraction, settlement of high compressibility soil such as marine clay, natural consolidation of alluvial soil or tectonic subsidence. Over the period of 1982-1997, the subsidence occurred from 20 to 200 cm, with the rates of about 1 to 15 cm/year, in several places. This paper discusses settlement induced land subsidence of shallow marine clay deposits on Kamal Muara area, based on the pore water pressure changes based on the piezometer's measurement located at 19 meters and 32 meters depth. Consolidation parameters (Cv and Cc) tested by cyclic load consolidation test. The estimation of on-site land subsidence is performed using the Terzaghi's 1-D consolidation theory and the secondary compression theory. Ranges of estimated values, as well as their relevant statistical properties, were identified. The results shown as follow: Without water extraction, settlement on soil layer #1 and #2 estimated as 0.647 meters and 0.305 meters respectively, with average subsidence rate is 9.832 cm/year and 1.07 cm/year. Total settlement estimated as 1.01 meters, with average subsidence rate is 5.07 - 5.42 cm/year. With water extraction, settlement on soil layer #1 and #2 estimated as 0.658 meters and 0.395 meters respectively, with average subsidence rate is 10.005 cm/year and 31.88 cm/year. The subsidence on Kamal Muara estimated as 0.68 - 1.05 meters, with subsidence rate 5 - 20.9 cm/year. The results placed on the lower range of field geodetical measurements, due to specific values of surface load and pore water measurement on Kamal Muara is used specifically.