Constructability Analyses of Vertical Extension Methods for Existing Underground Spaces

Remodeling underground structures requires careful construction planning, including consideration of costs and scheduling. Therefore, this study aims to analyze and compare the effects of four methods for vertically extending the underground spaces of an existing building under scheduling and cost constraints. The study considers the following extension methods: (1) bottom-up method, (2) normal top-down method after demolition, (3) normal top-down method in parallel with demolition, and (4) top-down method using double beams in parallel with demolition. Twelve illustrative examples are presented to investigate the constructability of these methods in terms of construction scheduling and costs. The construction durations and costs of each example is calculated and compared. We also analyze the structural stability of the examples using MIDAS Gen 2017. We conclude that the top-down method using double beams is the most efficient method in terms of costs and scheduling. The results and analysis process can help practitioners to select appropriate methods to expand underground spaces without demolishing entire existing buildings and efficiently manage costs and schedules. In future studies, these extension methods should be applied to real-world projects in various countries to validate and verify their actual effects on construction costs and scheduling.