Geo Talk 3 - HATTI
This activity was preceded by interactive presentations and discussions hosted by Mr. Prof.Ir. Chaidir Anwar Makarim, MSCE, Ph.D with the topic of Dewatering basement in Jakarta city - Perspective case since 30 years ago. Described very clearly and explicitly ranging from several cases that occurred due to dewatering in several buildings in Jakarta. The impact of groundwater on the construction process of a project is enormous. Water affects the design of structures, construction procedures and overall project costs. In this session we discussed five cases of building decline that occurred in Central Jakarta and North Jakarta for soft soil conditions. It was stated in his presentation that the damage caused by dewatering in soft soil is a common knowledge that often occurs in Jakarta. This is due to the reduction or settlement in which the soil pores that contain water decreases due to water sucked out of the pore. Destruction damage has occurred around the Grand Indonesia building, Bank Indonesia, Sarinah Building, Jakarta Box Tower Project (currently), and in other areas within a radius of up to ± 150 meters from basement excavation.
The conclusion of session 1 is as follows: • Pumping test must be present and the time is not enough for only 2 days. • Soft and dispersive soils may be simulated but must be conservative. • For projects with dewatering this required analysis of EIA.
In addition to the discussion sessions are also discussed on the aspects of the law and insurance for the condition if there is a case in dewatering. Not only during the presentation, the discussion between the participants and the experts turned out to be continued even though it has been interrupted by coffee break.
The next presentation was presented by Prof. Ir. Paulus Pramono Rahardjo, Ph.D with the topic "Examples of Inside Galian Cases in Jakarta and Considerations on Basement Construction Design". In this session he delivered about the excavations in South Jakarta, Central Jakarta, North Jakarta and excavations for MRT. In his presentation he also discussed problems arising from deep excavations such as: Stability issues during excavation, stability during long term periods, deformation and displacement, decrease in neighbors, dewatering problems and monitoring systems Also discussed commonly used excavation methods such as: Open Cut, open cut with reinforcement (SOIL NAILINGS), protection from excavation with plaster, berlin wall, soldier pile, diaphragm wall and additional stakes with Ground Anchor or Struts. In the drill design and monitoring system discussions are discussed about the design provisions of excavation such as safe design for basal heave, piping, artesian pressure, provision for global safety factor, maximum deformation of excavation system, maximum ground level reduction caused by excavation and due to dewatering system.
For discussion of the monitoring system discussed the movement of the retaining system, the horizontal movement of the retaining system, the decrease of ground around the building, groundwater elevation and pore pressures, visual observations of cracks or movements of neighboring buildings, forces in the retaining system and leaks / seepage and heaving.
The conclusion of session 2 is as follows:
• Excellent ground works can be done with open cut with minimum protection such as soil nailing, anchor, shotcrete. • The soil on soft soil will be a risk. • Drawing on underconsolidating soils requires attention to existing pore pressures and very low shear strength. • Monitoring on excavation is important as part of security, performance and warning systems (sometimes good for back analysis) • Determination of soil parameters is an important input.