Deep excavations in urban areas need to limit ground movements for the protection of surrounding property and generally have limited space for construction.
Top-down construction addresses both issues. Lateral earth support is provided by progressively excavating and constructing permanent robust supporting structures and the completed decks provide working space.
For the majority of underground railway stations bottom-up construction has been adopted. However top-down method can offer substantial savings with no temporary decks and eliminated or reduced temporary strutting.
For buildings with basements, time for completion can be reduced by many months. Early construction of the ground floor can permit early commencement of construction of the super-structure in parallel with completing the underground structures.
Designs and planning for construction of deep underground structures that take account of the interaction between the structures, whether temporary or part of the permanent structure, and the ground, and the method and sequence of construction can be cost effective and efficient.
John Endicott has been based in Hong Kong for some 40 years and will illustrate his talk with examples of using top-down and bottom-up methods in challenging situations such as the West Kowloon High Speed Rail Terminus.
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