A STUDY ON SAFE EVACUATION FROM INUNDATED UNDERGROUND MALL BY A MULTI-AGENT MODEL
Yutaro NAKASAKA, Taisuke ISHIGAKI(Kansai University, Japan) and Ryuji KAWANAKA(Hydro Technology Institute Co.,Ltd., Japan)

1. Introduction

3. Results

In the urban area of Japan, underground spaces, such as underground mall, subway stations, have beendeveloped to effectively utilize the limited land. However, in recent years, due to climate change, thenumber of heavy rainfalls has increased, and underground spaces are prone to inundations caused bypluvial flood. Therefore, it is important to perform quick and safe evacuation in the event of a disaster. In
this study, it was investigated how to improve the evacuation success rate in an underground mall in theurban area, assuming the possibility of underground flooding caused by pluvial flooding caused by shortterm torrential rainfall. The study area is a large-scale underground mall in the Umeda area in Osaka,
Japan. Figure 1 shows the location of Umeda. This area is very vulnerable to water-related disasters
because of its low ground level and rivers and seas on all sides. Figure 2 shows the mesh data andanalysis range of the underground shopping mall.

From the inundation results, the safe evacuation time starting from the start of rainfall is calculated. Thesafe evacuation completion time is obtained by using a criteria based on the specific force per unit width
for elderly female whose evacuation is difficult at the earliest time (Asai et al., 2010). Figure 5 shows thechange over time in the proportion of the area that can be evacuated. In this study, the safety evacuation
time is the time when the ratio of the safe evacuation area falls below 100%.
Figure 6 shows the results of the evacuation behavior simulation. The evacuation completion timeincreases as the number increases from 10,000 to 20,000. In this study, it was considered that theevacuation time increased because people settled at a specific exit because the following action was set
in order to consider the synchronicity at the time of disaster. It would be possible to shorten the evacuation
time if it could be set so that the route could be changed in the event of a guide or congestion.
Figure 7 shows a comparison between the average of evacuation time and the critical lines of the safe
evacuation time. In the case of 60 mm/hr, all patterns can be evacuated with almost no problem, but in thecase of 120 mm/hr and 180 mm/hr, as the number of people increases the evacuation margin timedecreases. In addition, even if you evacuate to the ground, it is conceivable that evacuation will be difficulton the way to the evacuation sites. In other words, it is dangerous to evacuate to the exit to the ground. Itis important for people to evacuate to the building connected in the underground shopping mall andevacuate to the upper floor in order to improve the evacuation success rate.

Fig.1 Umeda area, Osaka, Japan

Fig.2 Study area (Umeda underground mall)

2. Modela) Pluvial Flood Model
The inundation calculation was performed using InfoWorks
CS that can analyze ground inundation considering thesewer road network. The rainfall data are those createdusing three rainfalls of 60mm/hr, 120mm/hr and 180mm/hr.
The rainfall of 120 mm/hr and 180mm/hr are twice andthree times as large as the reference rainfall of 60 mm/hr,
the design rainfall in Osaka City (Kho et al., 2018). Figure
3 shows hyetographs of these rainfalls. These data arecentralized with a time interval of 5 minutes and a rainfall
duration of 2 hours.

Fig.3 Rainfall hyetograph (three types) (Kho et al., 2018)

Fig.5 The time variation of safe evacuation
area (elderly female)Fig.7 The evacuation time and critical lines ofsafe evacuation

4. Conclusionb) Evacuation Model: Multi-Agent Model
The evacuation simulation model was built by a multi-agent
simulation platform “artisoc 4.2” developed by Kozo Keikaku
Engineering Incorporated. Figure 4 shows a flowchart of evacuation
behavior. The study area is a one-dimensional network modelcomposed of nodes and links, and widths are set for passages.
Evacuees were set to adapt to changes such as speed reduction
due to congestion, and movement to a link with more people when
there were multiple destinations. Evacuation was simulated with six
patterns of 10,000, 12000, 14000, 16000, 18000, and 20000 visitors.
The simulation was performed 10 times for each pattern. All agents
started to evacuation when rain started, and the time which
everyone finish to evacuate was measured. After that, the average
evacuation time for each pattern were calculated.
Fig.4 The flowchart of the evacuation behavior

Fig.6 The box-plot of evacuation time
(10 times for 6 patterns)

It has been shown that the evacuation time decreases as the rainfall increases and the number ofevacuees increases. It has also been shown that evacuation methods of getting out to the ground andgoing to evacuation shelters were not an effective means to safely evacuate all evacuees if the floods
become severe. In the future, it will be possible to consider more specific evacuation success rates byconsidering when entering connected buildings and adding some guidance systems.

References⚫ Khoet al. (2018). Evacuation from inundated underground shopping mall under extreme weather condition,
Proceedings of Symposium on Underground Space, JSCE, Vol.23, pp.103-108. (in Japanese)⚫ Asai et al. (2010): SAFETY ANALYSIS OF EVACUATION ROUTES CONSIDERING ELDERLY PERSONS DURING
UNDERGROUND FLOODING, Journal of Hydroscience and Hydraulic Engineering, Vol.28, No.2 November, 15-21.