|Photo credit: AFP
By Hideaki Kimura, NTT Access Network Service Systems Laboratories
Urban planning aims to provide infrastructure that can withstand
disaster or that can easily be restored if it is damaged during
a disaster. Emergency communications are vital in providing
disaster relief, so access infrastructure for telecommunication
networks needs to be especially robust. At NTT Access Network
Service Systems Laboratories, we think that it is important to cooperate
with national and local government in building access
systems for telecommunication networks because the capital investment
in disaster-resistant infrastructure is huge.
Earthquake and tsunami
In Japan, infrastructure — and telecommunications infrastructure
in particular — has been put to the test by the biggest
earthquake ever recorded in the country’s history that struck at
14:46 hours on 11 March 2011 off the eastern coast of Japan.
The hypocentre was offshore from Sanriku at 38.1° north and
142.9° east, at a depth of about 24 km. The earthquake registered
9.0 on the Richter scale, seismic intensity decreasing with
distance from the hypocentre. The seismic intensity was 7 in the
northern part of Miyagi, up to 6 in southern and central Miyagi,
Fukushima, and below 6 in southern Iwate and southern Gunma.
And the earthquake triggered a huge tsunami, which swept
inland with a maximum height of about 38 metres, far exceeding
any previous assumptions.
The direction of the pressure axis of this reverse fault earthquake
was from west-northwest towards east-southeast. It was
a plate borderline earthquake, generated by the Pacific plate and
the boundary of the plate on the land. The maximum amount
of land shift was about 25 metres, and the scale of the fault
was about 200 kilometres in a north-south direction and about
500 kilometres in an east-west direction. The fault rupture expanded
in the vicinity of the point where the destruction began,
then progressed north and south, continuing for about three
||Photo credit: AFP/NASA
|Before (5 September 2010)
||After (This image was taken on 12 March 2011, and shows the
effects of the tsunami on Japan's coastline and inland)
Damage to general infrastructure
Cities, roads and communications infrastructure were damaged
by the earthquake and tsunami. What forces did the infrastructure
have to face, and how did it stand up to the disaster?
||Photo 1 — Damage caused by land liquidizing
|Inclination and subsidence of electrical pole
|Surfacing of NTT’s manhole
|Photo 2 — Damage caused by subsidence
|Broken bridge (side view)
|Photo 3 — Damage to road and railway
|Photo 4 — Access infrastructure equipment
|Photo 5 — Non-destructive diagnostic technology to monitor concrete
|Comprehensive supersonic wave method
|Photo 6 — Repair technology for cable accommodation tube
The scale of the disaster and its effects on infrastructure can
easily be seen from the maps and photographs shown here.
The two images shown above, from the United States
National Aeronautics and Space Administration (NASA), were
taken before and after the disaster. The image on the right was
taken on 12 March 2011, and shows how far the tsunami penetrated
inland, having flooded Miyagi and Iwate. Photo 1 shows
the damage caused by the ground liquidizing. This occurred in
the Itako-shi, Ibaraki, area, and caused both subsidence and
surfacing. Itako-shi, Ibaraki, suffered less damage than Miyagi
and Iwate, but the effects were significant. Photo 2 shows damage
caused by fill subsidence at the back of a bridge abutment,
with two views of the broken bridge and a picture of the broken
conduit. Photo 3 shows some of the other damage caused by
the earthquake and tsunami. A widening of the gap between
girders caused a bridge to fall. A dramatic landslip closed a
road. Sometimes infrastructure was deformed rather than broken,
for example the wavy road near the port or the undulating
Hitachinaka Kaihin Railway.
Damage to communications infrastructure
The disaster caused water leaks in the communications cable
tunnel. Pumping stopped because of loss of power, but the
communications cable was not affected and remained usable.
Concrete flaked off in the cable tunnel, but there was little damage.
The reason for this is because the cable tunnel was built
using technology that is in accordance with standards for earthquake
It might be asked why there was not more earthquake-resistant
infrastructure in Japan. The answer is depressingly simple
— because of the high cost of applying these technologies in
Access to communications infrastructure
The reliability of networks can be improved by means of:
network design technology, including the distribution of
data centres and the use of physically redundant transmission
network monitoring and control technologies;
building physical networks using improved earthquake-resistant
As a telecommunications carrier and a public corporation,
NTT is obliged to ensure the security of communications in the
event of disaster, in accordance with the measures enshrined
in law. This includes ensuring the security of access infrastructure,
which is, of course, essential for supporting communication
Access infrastructure comprises equipment such as conduits,
cable tunnels and manholes. In Japan, this infrastructure was all
constructed after 1950. Access infrastructure accommodates and
protects communication cables, such as metallic and optical fibre
cables, and provides access via manholes, as shown in Photo 4.
There are about 620 000 kilometres of conduits carrying cables
in Japan at present, along with about 650 kilometres of cable
tunnels large enough to permit human access (see Photo 4).
NTT has researched and developed various technologies that
minimize the impact of earthquakes on communication services.
To counteract the tension along the axes of conduits or tunnels,
caused by diastrophism resulting from an earthquake, NTT
has developed a telescopic joint and duct sleeve, both of which
can expand and contract.
To counteract equipment surfacing caused by ground liquidizing,
NTT constructs gravel drains around manholes. The effectiveness
of this technology was confirmed by a study of the
effects of the earthquake that occurred in the southern part of
Hyogo in 1995.
As a countermeasure to seismic ground motion at level 2 on
the Richter scale, (the maximum within the range of assumptions),
NTT has researched and developed various flexible technologies,
such as a flexible building access conduit, a flexible
excavation cable tunnel and a flexible shield shaft connection, to
protect communication cables.
Much of the equipment now in use in Japan was constructed
more than 30 years ago. About 75 per cent of cable tunnels and
about 40 per cent of conduits are at least 30 years old. More than
80 per cent of manholes are more than 30 years old.
Everyone understands the importance of basic equipment,
but there is almost no new construction because the capital cost
is so huge, and investment is now focused on the operation and
maintenance of equipment. Faced with the problem of controlling
investment costs, national and local government have to
make a choice between either spending money on the maintenance
and management of existing access equipment or on constructing
new earthquake-resistant infrastructure.
Future research and development
Continuing research and development to improve earthquake-
resistant construction technologies is clearly important to
ensure access to network infrastructure in the event of disaster,
so that telecommunications can be maintained. It is equally clear
that future research and development needs to focus on lowering
the cost of basic equipment.
Priorities will need to be set, taking into account the deterioration
NTT is researching and developing “check and repair” technologies
that can be used to monitor ageing equipment. Photo 5
shows two examples of non-destructive diagnosis technology,
which use two different methods to assess the deterioration of
concrete: the supersonic wave method; and the electromagnetic
method. The supersonic wave method is a technology for
assessing concrete thickness, the depth of cracks, the compressive
strength of the material, and corrosion. The electromagnetic
method is a technology for assessing the depth of cracks, along
with deterioration factors such as salinity.
If infrastructure is found to be deteriorating dangerously, it
must be repaired or replaced. Photo 6 shows technology that can
be used to repair two different types of cable accommodation
tube. Using this technology, it is possible to repair and reinforce
conduits that carry cables. This technology offers a way of maintaining
operations at low cost.
Learning from disaster
The earthquake and tsunami that struck Japan in March 2011
affected the access infrastructure essential to supporting communication
systems. Technologies now exist that are earthquakeresistant
but much current equipment is superannuated. A lot will
undoubtedly be learned from analysing the damage caused by
the March disaster. Meanwhile, NTT will continue to work on the
technologies for access construction that it has developed to date
to ensure that communications lifelines remain open.
* This article is based on contribution from the International
Policy Division, Global ICT Strategy Bureau of Japan’s Ministry
of Internal Affairs and Communications.