DEEP BASEMENT EXCAVATION IN SOFT BANGKOK CLAY CLOSED TO PALACES

Abstract

The Bank of Thailand (BOT) head office is a large building constructed in the inner
Ratanakosin Island of Bangkok along Chao Phraya River, a main river of Bangkok, where high-rise building
construction with more than three stories is not permitted. The BOT building consists of five basements with
excavation depth of 15.8 meters and only three stories of super structure. The soil condition consists of 15 m.
thick soft to medium clay followed by stiff silty clay and sand layer. The basement construction was
constructed only five meters away from Tewavej Palace and ten meters away from Bangkhunphrom Palace.
The damage assessment by means of Finite Element Method (FEM) with simulation of basement
construction method was carried out to predict the influence on both palaces. Finally, the top-down
construction method was selected for basement construction with one meter thick and 20 meters long of
diaphragm wall which was designed together with the 50 meters long bored pile to support the whole
building. The full set of instrumentation was installed at the palaces, diaphragm wall and ground surface for
monitoring the field performances and effect to the palaces during and after basement construction. The field
measurement and FEM prediction is compared and the time dependent of lateral wall movement is discussed.
The construction was completed without any damage or effect to both palace.