HAZARAD ANALYSIS OF SMALL UNDERGROUND SPACE IN URBAN FLOOD AND STUDY OF COUNTERMEASURES

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The main results obtained through this research are as follows.A three dimensional numerical simulation model is developed for inundation analysis in a small underground space. VOF method is used in the model. The model is verified, comparing several computation results with the experimental data of a full-scale stairs model and of a 1/15-crate basement model comprising two stairs, corridor and five rooms. It is found that the model can well simulate the inundation flow behavior in the basement. We conclude that the model can be applicable to evacuation analysis in a small underground space.Evacuation from underground space has been investigated by using two real size models of staircase and door. From the experiment of staircase, we find that the water depth of 0.3m on the ground level is the limit of safe and easy evacuation and that clothes are also related with evacuation. In addition, specific tire per unit width is introduced as a new criterion to evaluate safety evacuation in both corridor and staircase. It is difficult to implement safety evacuation when the specific faro per unit width is over 0.125m^2. From the experiment of door we find that the water depth in between 0.3m and 0.4m in front of the door is the limit to open it without difficulties. Also, we have to keep in mind that evacuation by children or elderly people is more difficult than that by adults.Through the simulation results by the integrated urban flood model with 2-D underground inundation model, we find that setting of step at each entrance is one of the effective measures to reduce the risk at underground inundation, especially for heavy rainfall for a short time.