STABILITY ANALYSIS OF DEEP EXCAVATION IN JAKARTA MRT STATION

• Main Author: Khaedar Nuridwan Putra, Kevin
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/74644
• Institution: Institut Teknologi Bandung

Construction of underground structure is complex work. The unloading process carried out during construction can change the stability that occurs. This report discusses about analysis of excavation that located in Mangga Besar MRT Station. The project has an excavation depth 30.8 m and a width of 14.1 m. Retaining structure used is a diaphragm wall using temporary struts and kingpost to increase stability during due to construction period. There are two locations that are analyzed in this report, namely section A and section B. The striking difference between those two sections is the presence of a layer of sand found at depth 0f 42 m to 48 m in section A. This analysis used PLAXIS 2D software by using hardening soil model. The conditions reviewed in the analysis are undrained without seepage, undrained with seepage, and drained. After analysis, it was found that the presence of a layer of sand at depth of 42 m to 48 m in section A affects the depth of the diaphragm wall installed. The wall depth must be at the cutoff depth or cut through the sand layer to prevent upheaval failure at the bottom of the excavation. Then used diaphragm wall with thickness of 1.2 m and depth of 50.8 m for section A. Meanwhile in section B, diaphragm wall with thickness of 1.2 m and depth of 50.8 m is installed. Excavation work carried out causes negative excess pore pressure. If there is a delay in construction of the excavation, the negative excess pore pressure will dissipate as a function of time. In addition, delay of construction can also make the flow that occurs towards a steady state. This makes drained condition the most decisive condition by obtaining the smallest safety factor. The global safety factor in section A and section B is 1.79 and 1.66 respectively. Then related to the stability of the bottom of the excavation, safety factors of 1.75 and 1.95 for basal heave, 1.51 and 1.52 for sand boiling, 1.29 and 1.27 for upheaval. There are also lateral deformations and maximum land subsidence that occur in each section of 5.31 cm and 2.27 cm for section A and 4.69 cm and 2.10 cm for section B. From the internal forces, it is recommended to install 35D32 flexural reinforcement and D13-300 shear reinforcement in section A. While in section B 28D32 for flexural reinforcement and D13-300 for shear reinforcement. In addition, it is also recommended to use struts with dimensions of 700 mm x 300 mm.