Special Feature

Disaster Prevention and Security Technologies
Contributing to Safe and Secure Networks
Hideki Uehara, Susumu Baba, Koji Tanaka†,
and Taishi Deguchi
Abstract
To protect communications networks from large-scale earthquakes, we are conducting research anddevelopment of earthquake-proof technology for underground communications facilities and of seismic
evaluation methods. We are also deploying optical fiber sensing technology, which can measure the distortion or deformation of structures, in business applications outside NTT to allow precautions to betaken against possible accidents. This article introduces disaster prevention and security technologies forsupporting infrastructure equipment in communication networks.

1. Earthquake-proof technology supporting
network reliability
In Japan, people are becoming more aware of thepower of earthquakes and the damage they can cause
following several recent large-scale earthquakes,
such as the 2004 Niigata Chuetsu Earthquake, andpredictions for large-scale earthquakes in the near
future announced by the government. Accordingly,
we have given a high priority to the development oftechnologies for constructing earthquake-proof networks to ensure the reliability of future broadbandubiquitous communications services. Seismic countermeasures for NTT’s underground facilities havebeen developed and improved based on analyses ofdamage caused by actual earthquakes in the past.
Because level-II earthquake motions (equivalent toseismic intensity 7) were defined by JSCE (JapanSociety of Civil Engineers) after the 1995 HanshinAwaji earthquake, we have been implementing seismic evaluations methods and earthquake-proof countermeasures for underground facilities according tothis new standard.

† NTT Access Network Service Systems Laboratories
Tsukuba-shi, 305-0805 Japan
E-mail: kojit@ansl.ntt.co.jp

Vol. 4 No. 6 June 2006

2. Seismic countermeasures
2.1 For cable tunnels
Cable tunnels are designed to withstand a largescale earthquake with level-II earthquake motions,and cables inside cable tunnels were not damaged
even in the 1995 Hanshin-Awaji earthquake. However, water leakage and flooding did occur at connections, so we decided to develop the following countermeasures.
(1) Flexible joint for open-cut tunnel
We have developed a flexible joint because relative
displacements occurred in some cases at the attachment point between a building and a vertical shaft
when the open-cut tunnel expandable joint was in liquefied ground (Fig. 1(5)).
(2) Flexible joint for connection in shield tunnel orvertical shaft
As cracking and water leakage were seen in somecases at the attachment point between a shield tunnel
and a vertical shaft, we have developed a joint thatcan withstand water pressure and can expand andcontract lengthwise to maintain the high reliability ofcable tunnels (Fig. 1(4)).
2.2 For conduit lines
Since a conduit line may be damaged by grounddeformation caused by an earthquake, we are improving earthquake resistance by making the connection
41Special Feature(1) Sliding joint for manhole
ducts (duct sleeve)(2) Sliding joint for conduits(3) Sliding joint with astopper

Customer’sbuilding

Flexiblejoint

Open-cuttunnelSliding joint+
duct sleeve

Vertical shaft

NTT’sbuilding

Sliding joint
with a stopper+
protective
concrete

MHMH

ShieldtunnelFacilities attached
to a bridge

Normal ground(4) Flexible joint for connecting shieldtunnel and vertical shaft

Sliding joint
with a stopper+duct sleeve

SFRCMH

HH

MH: Manhole
HH: Handhole
Liquescent ground(5) Flexible joint
for open-cuttunnel(6) Flexible building
access conduits
Relativedisplacements

HH

Buildingwall
Corrugated flexible conduit

Fig. 1. Seismic countermeasures for NTT’s underground facilities.

part flexible.
(1) Sliding joint for conduits
We have changed the joint structure from screw
type to sliding type to improve earthquake resistanceand to make construction work more efficient (i.e.,faster and easier) (Fig. 1(2)).
(2) Sliding joint for manhole ducts (duct sleeve)
We introduced a duct sleeve, which acts as a sliding
joint, to enable connections to manholes to follow to
the shape of ground deformation (Fig. 1(1)).
(3) Sliding joint with a stopper for conduits
By applying a sliding joint with a stopper to areas
such as those susceptible to liquefaction and thosewith bridge sections, we have improved the reliability of conduit lines because the stopper limits therange of movement. (Fig. 1(3)).
(4) Flexible building access conduits
We installed a flexible building access conduit leading between a handhole and a customer’s building to42

absorb large relative displacements due to uneven settling of the ground (Fig. 1(6)).
2.3 For manholes
As the duct part of a manhole is a connection pointwith the conduit, a large relative displacement may begenerated in an earthquake, causing flaking of concrete blocks or damage to communications cables.
We have improved its ability to withstand heavyloads by introducing steel fiber reinforced concrete(SFRC).
2.4 For telecommunications bridges
Telecommunications bridges are special bridges
that are used when NTT’s communications cables
cross a river or other obstacle. About 3000 telecommunications bridges are in place across Japan. They
range in length from several meters to several hundred meters and there are various types of bridge
NTT Technical Review

Special Featureincluding rolled-beam bridges and truss bridges. A
telecommunications bridge is a structural component
consisting of infrastructure facilities together withconduits, manholes, and cable tunnels. Unlike otherinfrastructure facilities, they are located on theground instead of underground, so they are easily
affected by seismic motions. That makes them possibly the weakest point of infrastructure facilities. Infact, damage such as the breakage of supports, buckling of main girders, and depression of the rear sidesof abutments has occurred in past earthquakes (Fig.
2).
Telecommunications bridges have light bridge
beams because the load to be supported is smaller

than the load on a road bridge, and they are narrow
because they only carry communication cables. Thus,
their design goals differ from those of road bridges.
For these bridges, it is important to prevent themfalling in a lateral direction. To implement seismic
countermeasures efficiently and effectively, we rated
the earthquake resistance required for telecommunications bridges taking into account the possibility of
secondary damage occurring and the importance ofthe facilities. From that we determined whether or not
it is necessary to apply the measures. In cases where
there is a danger of secondary damage resulting frombridge collapse, we will implement the required seismic countermeasures as a fail-safe (Fig. 3).

Conduits

Main girder is bent

Support is broken

AbutmentRear side is depressed

Fig. 2. Damage that occurred in past earthquakes.

Telecommunications bridges:
about 3000
Divide by degreeof importance

To apply earthquake-resistant countermeasures effectively andefficiently to about 3000 telecommunications bridges, classify
them in two ranks (A and B) according their importance.

Determine necessary
earthquake-resistivity

Determine the need for earthquake resistance for eachtelecommunications bridge.

Judge level-II durability

From the results, judge whether the bridge has level-II durability
from the bridge type, bridge length, and the number of attachedconduits.

Judge the need for fail-safe

Judge from the installation environment whether secondary
damage may occur.

Decide necessary
countermeasures

Judge priority

Decide the required seismic countermeasures according to theimportance, level-II durability, and need for a fail-safe.

Determine where countermeasures
will be applied

Fig. 3. Flow for deciding the seismic countermeasures for telecommunications bridges.

Vol. 4 No. 6 June 2006

43

Special Feature

In the future, we are planning to evaluate the earthquake resistance of the cable conduits attached toroad bridges, in addition to improving the ability ofroad bridges to resist earthquakes by, for example,
making them seismically isolated.
3. Evaluation of seismic performance of accesssystem underground routes

Underground cablefacilities data layer

Facility
dataFacilities

To implement seismic countermeasures on a vastquantity of underground facilities efficiently andeffectively, it is necessary to evaluate the equipmentfrom the viewpoint of the possibility of it sufferingdamage and to execute appropriate countermeasuresaccording to priority assessment within a limited
budget. As a tool for doing this, we have developedsoftware for evaluating the seismic performance ofunderground facilities. It can evaluate their earthquake resistance based on 1) information about thefacilities (available from various in-house shared
databases), the ground (detailed geological data
about Japan), and earthquakes (magnitude, epicenter,depth, etc.) and 2) the probability of damage estimated from historical damage data such as that for the
1995 Hanshin-Awaji earthquake (Fig. 4).
By performing simulations with this software

before an earthquake occurs, we can predict the seismic intensity and occurrence of liquefaction in specific areas and utilize the results to make effectiveplans for updating equipment taking into account theimportance of communications lines and to selectappropriate countermeasures. In addition, this software will help us in making plans for surveying damage and performing restoration work after an earthquake. And it will be useful in actually implementing
effective restoration by making it possible to executeprioritized restoration work, beginning from the mosteffective place or in making a restoration plan incooperation with other lifeline companies that also
have underground facilities (Fig. 5).
At present, we are adding damage probability datathat was obtained from cable damage data and experimental results. This is enabling us to enhance thesoftware’s ability to identify the weak points ofaccess system underground routes so that we caneliminate them.
4. Optical fiber sensing technology
Brillouin optical time domain reflectometry(BOTDR) is an optical fiber sensing technology
developed by NTT [1]. It has been put into practical

Damage probability
comparison table

Display of cable damage locations

Ground-boringdata layer

Detailed topographicclassifications layer

Earthquake
data

Location of seismic
center, magnitude,related information

Seismic intensity

Grounddata

Damage simulation

Infrastructure facilities
data layer (conduits, MHs)

Liquefaction danger
level map layer

Actual data ofHanshin-Awaji earthquake

Max conduit spandamage probability_ X < 0.05
0.00 ≤
0.05 ≤_ X < 0.100.10 ≤_ X < 0.15
0.15 ≤_ X < 0.20
0.20 ≤_ X < 1.00

Area withhigh possibilityof damageNTT’s building
Liquefaction
judgment
No liquefaction
Liquefaction

Area with low
possibility ofdamage

Develop cabledamage evaluation
softwareFig. 4. Algorithm of evaluating the seismic performance.

44NTT Technical Review

Special Feature

Average possibilityof conduit damage
0.00 ≤_ X < 0.05
_ X < 0.100.05 ≤0.10 ≤_ X < 0.15
_ X < 0.20
0.15 ≤_ X < 1.00
0.20 ≤

Simulations before
an earthquake occurs

Restoration work after
an earthquake occurs• Change to duct sleeve.
• Reinforce with lining.
• It removes the new route plans
where the probability of damage
is high.

• Decide priority of restoration andcreate a restoration scenario.
• Make a restoration plan incoordination with lifelinecompanies neighboring thedamaged location.

Fig. 5. Examples of effective simulations.

use in a communication tunnel management system
and it has been customized and introduced for disaster prevention and security for social infrastructures
such as roads, tunnels, and bridges by NTT Group
companies such as NTT InfraNet. BOTDR is attracting global attention as an alternative to conventional
electrical sensors. For example, it is currently being
examined for use in monitoring deformations inunderground mines (Fig. 6).
(1) Slope collapse monitoring function
Across Japan, disasters frequently occur as a resultof landslides caused by heavy rains or storms. We
have developed optical fiber slope displacement,
underground displacement, and water-level sensors
to quickly provide information about the possibilityof disasters, even small landslides, within a large
monitored area.
(2) Bridge monitoring function
Bridges are very important facilities. They are
strategic points in times of disaster as well as being
vital for day-to-day transportation and traffic. Therefore, performing maintenance and management,
ensuring safety, and improving earthquake resistanceare critical themes for road administrators. We havedeveloped a small optical fiber displacement sensor
that can detect and measure the amount of displacement of bridge beams to enable us to evaluate thebridge’s condition and decide whether it is safe toVol. 4 No. 6 June 2006use.
(3) Tunnel monitoring function
Communication tunnels are places where many
communication cables are concentrated, so theirstructural performance must be maintained for very
long periods of time. We are using optical fiber sensing technology to monitor the amount of tunnel
deformation caused by nearby construction work. In
recent years, accidents involving concrete flaking off
and concrete fragments falling from the ceilings ofroad and railway tunnels have been reported. For
such cases, our optical fiber sensing technology has
been attracting attention as a way to perform multipoint measurement on long-span structures effectively and remotely.
(4) Example of applications abroad
The use of information technology (IT) in the mining industry is rapidly progressing around the world
and optical fiber sensing technologies are expected to
be introduced in this field soon. At present, we areconducting joint feasibility tests of mine tunnel monitoring methods in Chile with a local copper mining
company [2]. By monitoring the rock deformation
caused by mining operations, we can pick up signs ofimpending disaster such as rocks falling from the tunnel ceiling. We are conducting experiments to verify
the reliability of optical fiber sensing systems under
severe conditions and to establish a system that can45

Special Feature

Example of application abroad (Chile, monitoring mine tunnel)

BOTDR measurement principle
Optical fiberChile

Pulsed light

Minetunnel

Signal power

DBrillouin
ε1 istort scattered light
ε2 ionε3Di Z1stancZ2e

νB2
νB1 calti
Op uency
freq

NORTE
GRANDE

IquiqueCalamaAntofagasta San Pearode Atacama

NORTE Copiapó
CHICO

BOTDR

La Serena
Isla
Coquimbode Pascua
Vina del Mar Mantegua
Valparaiso
Santiago
CENTRO
RanteguaArchi. Juan
Taica
Fernández
ChillanConcepcion
TemucoSUR

Road slope
TunnelDam

Arica

Valdvia
Ancud
CastroOsarno
Puerto Montt

PATAGONIA
NORTE

Puerto Alsan
Coihalquo

PATAGONIA
SUR

PuartoNatales
Punta
ArenesMonitoring collapse of slope
Building

Optical fiber undergrounddisplacement sensor

NetworkPlantJapan
BridgeRemote support PC

Optical fiber slope
displacement sensor

Fixed point

Undergroundfacilities

Optical fiber
water-level sensor

Tunnel monitoring (neighboring construction)
New orNTT
updatingbuilding
Construction
work ofwork ofundergroundtunnelfacilities

Bridge monitoring

Small optical fiber
displacement sensor

CabletunnelFig. 6. Overview of BOTDR.

ensure the safety and efficiency of mining operations.
Changes in the rock status are monitored continuously in both the local office in Chile and in Japan via anetwork. Field test results to date show that the experimental system accurately caught changes in the tunnel caused by excavation and confirm the applicability of optical fiber sensing to efforts to improve minesafety against disasters. We are planning further
deployments of optical fiber sensing technologies totest its applicability to other applications.

46

References
[1]

[2]

K. Fujihashi, H. Uehara, M. Okutsu, and K. Komatsu, “Developmentof a Road Disaster Monitoring System Using Optical Fiber Sensing
Technology,” NTT Technical Review, Vol. 1, No. 9, pp. 48-52, 2003.
K. Nozawa, K. Noguchi, M. Shoji, H. Uehara, and R. Ohmoto,“International Joint Feasibility Experiment with a Copper-mining
Company in Chile,” NTT Technical Review, Vol. 4, No. 1, pp. 44-49,2006.

NTT Technical Review

Special Feature

Hideki Uehara

Koji Tanaka

Senior Research Engineer, Supervisor, Civil
Engineering Project, NTT Access Network Service Systems Laboratories.
He received the B.E. degree in civil engineering from the University of Tokyo, Tokyo, in1983. In 1983, he joined Nippon Telegraph andTelephone Public Corporation (now NTT),
Tokyo. He worked mainly in the telecommunication facility planning section. After 2000, he
worked in the multimedia communication section and the customer service section. He took up
his present post in 2003. He is a member of theJapan Society of Civil Engineers (JSCE) andJapan Association for Earthquake Engineering.

Research Engineer, Civil Engineering Project,NTT Access Network Service Systems Laboratories.
He received the B.E. degree in civil and environmental engineering from Yamanashi University, Yamanashi, in 1990. He joined NTT in 1990
and developed no-dig repair technologies forunderground conduit lines. In 2005, he was transferred to NTT Access Network Service SystemsLaboratories. He is currently engaged in researchon earthquake-proof technology. He is a memberof JSCE.

Susumu Baba

Taishi Deguchi

Research Engineer, Civil Engineering Project,
NTT Access Network Service Systems Laboratories.
He received the B.E degree in civil engineeringfrom Kisarazu National College of Technology,Chiba, in 1980. He joined Nippon Telegraph andTelephone Public Corporation (now NTT) in1980. Recently, he has been engaged in researchon earthquake-proof technology.

Research Engineer, Civil Engineering Project,
NTT Access Network Service Systems Laboratories.
He received the B.E. degree in civil engineering from Kanazawa University, Ishikawa, in1992. He joined NTT in 1992 and was transferred to NTT Access Network Service Systems
Laboratories in 2003. He is currently engaged in
the development of applications using BOTDR.

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