Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 621

Table 23.1 Pipe materials used in the distribution area of the
water-supply system

Pipe length (m)

CIP DCIP Steel Pipe

Dia.
(mm) Old Old New Old New

200 4 738 20 091 0 1 390 0

250 52 53 0 0 0

300 3 620 14 898 0 925 0

350 2 820 14 049 0 2 121 0

400 0 0 0 879 0

500 0 7 000 5 260 0 23 023

Subtotal 11 230 56 091 5 260 5 315 23 023

Total 100 919

Source: Wada et al. (2010).

If transmission pipelines are broken, the water supply may be suspended
due to pipe damage and repair works. On occasion, seismic damage within
the distribution network may be limited to particular service areas by
means of emergency shut-off valves. These different characteristics of trans-
mission and distribution pipelines are refl ected in the pipe materials and
their joint systems.
Transmission pipelines have to be strong enough to withstand earthquake
loads; as a result, arc-welded high-grade steel pipes are often adopted.
The distribution and service networks, on the other hand, include old
cast-iron pipes (CIP) with bell and spigot joints as well as ductile cast-iron
pipes (DCIP) which are classifi ed into two different joint types: unrestrained
joint (old type) and new restrained joint (new type) (Kubota, 1992). As
a result, the weakest joints of CIP are particularly vulnerable to seismic
damage.
The main target of seismic retrofi tting activities is to replace old-type CIP
and DCIP with new DCIP or arc-welded steel pipes in the distribution
network system. Recently in Japan, newly developed restrained-segmented
joint pipes have been widely used to replace old unrestrained pipes as part
of seismic disaster-prevention measures. Mechanical features of old- and
new-type CIP and DCIP joints are illustrated in Fig. 23.3. Since CIP and
DCIP with old-type joints do not have any restraining mechanism for axial
force, they are vulnerable to seismic displacement. As a result, these unre-
strained pipes with old-type joints are replaced by new-type DCIP, which
is equipped with a locking mechanism and thus cannot be easily pulled out