避難シミュレーションを用いた大規模地下街津波浸水対策の避難誘導計画の評価

抄録

　Underground spaces are widely developed in many large cities in Japan. Therefore, social and economic risk management of underground mall against tsunamis caused by major earthquakes is required. When the Great East Japan Earthquake struck in 2011, a tsunami of greater-than-expected proportions caused extensive flooding in large areas, and then forcing a fundamental review of disaster prevention measures. Administrators of underground malls and other facilities in the Tsunami Hazard Area were obliged to prepare and publish Tsunami Evacuation Plans (Act on Development of Areas Resilient to Tsunami Disasters，2011). Predicting the behavior of evacuees during a disaster is important to evaluate the safety of such evacuation plans. However, there are challenges in predicting evacuee behavior and verifying the safety of evacuation plans for various disaster situations.

　This study aims to quantitatively evaluate the improvement of evacuation safety following the revision of the evacuation plan for tsunami disaster in a large underground space. Several scenarios developed by the management company (under consideration) were simulated at the most congested time of day (18:00 on weekdays), and a comparative study was conducted. The main findings are as follows.

1）　Evacuees chose the shortest staircase to evacuate by themselves or were guided to evacuate in groups by the management company, and both scenarios were completed within the target time of 120 minutes.

2）　Simulations of a scenario in which evacuees choose the shortest staircase and evacuate on themselves revealed a bottleneck staircase.

3）　the Plan for dispersed evacuation through evacuation guidance and the plan to direct people to the widest staircase even if the distance was disadvantageous were more effective than the plan to select the staircase at the shortest distance. And then the time and amount of the effect were quantitatively shown by simulation.

4）　In the case of a group evacuation, the efficiency of evacuation to the ground was better if there were more evacuation stairs due to the dispersion effect. However, there are still some points to be noted regarding the safety of the overall evacuation, such as the choice of the evacuation movement routes on the ground and the capacity of the walkways.

5）　The visualization of the distribution of evacuee retention revealed the location and time of evacuee retention for each evacuation scenario, demonstrating the potential use of the simulation to support evacuation guidance planning.

6）　We were able to visualize the bottlenecks that occur when dividing up areas that are difficult to identify by numerical analysis.

　In summary, we were able to evaluate part of the evacuation safety from the perspective of evacuation guidance by comparing each scenario (evacuation timeline) considered by the management company by using evacuation simulation.