CONSTRUCTION TECHNOLOGIES FOR IMPROVING THE SAFETY OF DEEP EXCAVATION WORKS AND THE SURROUNDING STRUCTURES

Abstract

In many countries today, the number of deep excavation pits is increasing yearly, due to the increased necessity to satisfy the growing land needs. A significant amount of deep excavation works has also been undertaken in the Kallang Formation, which involves significant risks such as settlement of adjacent properties and utilities. Large-scale deep excavation projects also have the potential to injure or cause inconvenience to not only the workers involved, but also to the public. The infamous example of deep excavation collapse is the excavation adjacent to Nicoll Highway, which resulted in 4 fatalities. In this study, the construction technologies used in the industry is explored to ensure the safety, stability and robustness of deep excavations, minimizing the impact of settlement of adjacent structures. This includes utilizing “Top-Down” construction approach and the installation of diaphragm wall, cross walls, soil improvement, kingposts, strutting and recharge wells, coupled with instrumentation and monitoring. A case study of the deep excavation at the ongoing Jalan Besar Mass Rapid Transit Station project is adopted. From the construction technologies in placed at site, the way the industry has incorporated the lessons learnt from past construction deficiencies can be seen judging from the emphasis placed on temporary supporting structure works. From the case study, problems faced at site are mainly the diaphragm wall deflection and settlement of adjacent conservation shophouses despite the implementation of Earth Retaining Stabilizing Structures. Solutions suggested include the use of Tube-A-Manchette Grouting and Jet Mechanical Mixing methods. However, the limitations of this paper is that only one case study is studied in detail, and cannot be generalized to all deep excavation projects in the industry. In addition, as this report only focuses on the implementation process, it cannot guarantee the safety and robustness of deep excavation works, unless proper design is involved.