Failure Knowledge Database / 100 Selected Cases

A concrete wall collapsed under drainage channel improvement
work in Tottori【The accident date : Afternoon in December 20th, 1972
The accident place: Yurayado Daieicho Tohaku District Tottori Prefecture】
Writer：Masahiko Kunishima・Keita Sugihara（note 1）

1.

Event
In December 20th around 13:20 in 1972, the side wall (1.1m height, 22m length, 25cm

width, made from concrete) collapsed onto construction workers during the excavation
phase of drainage channel improvement work in a Hojosakyu prefecture-run
agricultural field at the north-side of the Yura elementary school in the Tohaku District
Tottori Prefecture.
Seven female workers, including Ms Ikuko Arao, who were the part-time workers
working during the farmer's leisure season, were crushed to death and a worker
received seriously injury. Three male workers managed to escape.
[Death: 7 (all were women), Serious injury: 1 (woman), Slight injury: 1 (man)]Figure1- Place(Source: Mainichi Newspaper)

Picture1-Situation of accident(Source: Mainichi Newspaper)-1-Failure Knowledge Database / 100 Selected Cases

2. Course
That day, about 15 cm of water accumulated in the drainage channel because of thelong spell of rainy weather, and the ground became soft. Moreover, the concrete sidewall had been embedded in the ground about 10cm, and the ground was dug about 15
more centimeters a week before. Therefore the side wall was very unstable. In addition,no safety countermeasure had been made just before the accident, and the foreman incharge of the excavation hastily supported the concrete wall with logs, sensing from thegush of the water during excavation that they were in danger. However, unfortunately,
the collapse of the concrete wall began, when the third brace member were being
installed.
Workers could not escape from the collapse, because they were working with theirhead, bent down to lay the cobble at the bottom of the drainage channel; also, since dug
up soil had been heaped up on the side of the drainage channel, they could not climb up
from the drainage channel.
As a result, 8 female workers and 1 male worker failed to escape, since the concretewall, which was over 22m in length, collapsed and were buried under the concrete wall.
More than 100 teachers and pupils’ fathers and mothers participated in the rescue,since there was a class round-table conference at Yura elementary school on that day.
But, unfortunately, the concrete wall was so heavy that they could not save the victims.
30 minutes later, the rescue was carried out using the bulldozer, but 6 workers were
instantly killed and one was killed in hospital where he had been carried.
The Yatsuhashi Police Station investigated the construction company over whether
there was any omission in the safety management, and, on the night of the 20th, Tetsuo
Izumi, who was in charge of the construction site, was arrested on charge of professional
negligence leading to death.

.

The outline drawing of the accident

Figure2- Simple figure of the accident(Source: Author made)-2-

Failure Knowledge Database / 100 Selected Cases

3. Cause
1.

The concrete wall gradually moved and suddenly collapsed because of the soft
ground of the drainage channel due to an accumulated 15 cm- depth of water,
and the weight of the soil heaped up on the side of drainage channel.

2.

The workers failed to escape, because they worked with their heads bent down
and were late to notice the collapse of the concrete wall.

3.

The concrete wall was very unstable, because they had dug down 15cm one
week before that day, even though the wall was embedded only 10cm in thedrainage channel bottom.

4.

Since the soil had been heaped up on the side of the drainage channel, it wasdifficult for the victims to escape from the collapsing wall, even if they had
noticed the collapse of the concrete wall.

5.

They did not do anything to support the wall just before the accident took place,nevertheless they should have made bars to support the wall within every 1.5m
to prevent the collapse of the wall.

1.5m

Side wall

The figure of the ideal distribution of support bars to support(Source: Author made)6.

Even though this sort of construction work should be started after the side wallis removed, in this construction, the drastic design change was done to recycle
the walls in order to reduce the cost, following the request of Tottori Prefecture.

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4. Immediate Action
1. The field chief sensed the danger and tried to make support bars using logs, but
unfortunately, the collapse of the concrete wall had begun.
2. The worker near that place witnessed the collapse of the concrete wall and, inorder to rescue the victims, called other workers who were working in an
agricultural field about 200m away from that place and the teachers and theparents who attended the Round-table conference of Yura elementary school.
But the rescue was not carried out successfully, because the concrete wall was soheavy that they could not remove the wall. 30 minutes after the accident,bulldozers and shovel cars arrived and started breaking the concrete to savethem.
5. Countermeasures
Due to this accident, the Safety and Health section of Tottori Labor Standards
Inspection Office increased the access to guidance on the support bars for the concreteside wall in case of this kind of construction.
6. Knowledge
In the construction field, which holds so many inexperienced workers, further safetycontrol should be conducted on materials and safety education than in the normal
construction field.

For instance, suggestions on this issue are below.

The aspect of safety control on materials
1. There is no support bar for the concrete side wall.
2. Some treatments should be conducted for the looseness of the ground after a longspell of rainy weather.
The aspect of the safety education
1. The field manager should inform the workers of the danger for banking up dug
soil on the side of the concrete side wall.
However, even if there had been a lot of experienced workers, this accident would havehappened, because the safety control on materials was clearly not sufficient. It isdefinite that not making support bars for the wall standing almost vertically was very
dangerous, when working in the drainage channel. Also, even though they can savemoney, changing the design in order to recycle the wall increased the possibility of theaccident; normally, they have to start construction after removing the concrete side wall.
Moreover, this accident should be predictable enough, because the field managers knew-4-Failure Knowledge Database / 100 Selected Cases

that the ground was loose and the bottom of the concrete wall was revealed.

In thefuture, it is necessary that field managers CONTROL MATERIALS SAFELY,EDUCATE CONSTRUCTION WORKERS PROPERLY, PREDICT THE POSSIBLE
ACCIDENT BEFOREHAND, DO NOT REDUCE SAFETY COSTS FOR THE SAKE OFOBTAINING MORE PROFIT.
7. Background
One of the factors of this accident might have been the appointment of theinexperienced workers to this construction. Why were the inexperienced workers, whoshould have been more closely directed than experienced workers, involved in thisaccident, and became the victims? The background is described in the following.
1972 experienced the excess production of the yam which is locally produced in Tottori.
The yam was supplied to such an extent in the market that the price of yams was quite
low. Farmers could not get a decent amount of money; therefore housewives had to
obtain money for the New Year. That was the reason why they had to work in theconstruction site, which they were not used to. On another front, there were two reasonsfor Umano Construction Company was forced to employ inexperienced female workers.
One was that they were such a small company with only several hundreds of employeethat they had to get human resources locally. The second reason was that there were asmall number of male workers in those days.
8. Generalization
It can be said that this accident was, in some senses, inevitable for Umano
Construction Company. This is because, since there was a shortage of human resources
due to the high economic growth, Umano had to employ inexperienced workers, andthey were required by Tottori Prefecture to change the design, which increased the riskof the accident. However, there still remained Umano’s faults, because they did not
distribute support bars for the wall sufficiently, continued working in spite of the loose
ground, and were so late to respond to the accident. In addition, they should haveconduct further safe education than usual, because they employed a great amount of
inexperienced workers.
Also, it is undoubtedly true that there was a trend of neglecting safety, inferring fromTottori Prefecture’s request for the design change even though the design change raised
a risk.

-5-Failure Knowledge Database / 100 Selected Cases

9. On the SideIn this accident, the excavation was carried out by manpower; though it was legal, it
had been planned to be dug by machinery. However, if the mechanized excavation had
been done, lives would not have been lost, even if the collapse happened.

Reference： Yearbook of Construction Safety and Health (1973 fiscal year), Nihonkai
Newspaper (21st and 22nd December 1972), Asahi Newspaper (21st December 1972),
Mainichi Newspaper (21st December 1972), Yomiuri Newspaper (21st December 1972)(Note of 1) 4th grade undergraduate student of Civil Engineering Dept in Univ. of Tokyo-6-