Different Methods of Excavation for Basement in Jakarta: Design, Reality and Associated Problems

摘要

Jakarta is a wide area covering different soils conditions and different surrounding. As metropolitan city, Jakarta has serious problems due to difficulties in the methods of excavation, geology, water table, and disturbance to neighbors. Of particular interest is there is no fixed standard of design and each designer has used different methods and references. Many constructions have been successful, and some construction fail due to lack of understanding and knowledge on the soils condition. The soft soils condition is part of the cause of failures. These soft layers spread from south to north of the city owing the fact that old or ancient rivers were there and at present, they could not be identified after covered by sediments. Soil Investigation should be carefully planned to reveal the variety of ground condition. In most cases, the soft soils are still consolidating and hence some failures have been caused due to ignorance on the presence of excess pore pressures. On the other hand, in some areas strong lahar formation also exist and excavation lead the fact that they are stable upon deep excavation over 15 m even without protection or minor treatment. The area could change drastically within a distance of less than 50 m. In central Jakarta surrounding the National Monuments, loose to medium sands are found. The excavation dewatering has caused severe problems mainly settlement of neighborhood that subsequently sued the owner of the buildings. The City of Jakarta now prohibit dewatering by pumping during excavation. The methods employed by designers and contractors vary depending on their experiences. Lessons learned from success and failures have been documented by the author. This paper discusses case histories of all common methods of excavation for the basement in Jakarta City from design perspectives and facts of recorded failures as well as successful measurements. A discussion on deep excavation for Jakarta MRT is also presented.