Research Trends and Results

Countermeasures against large-scale earthquake insewage system based on the damage of Great East
Japan Earthquake
YOKOTA Toshihiro, HeadFUKATANI Wataru, Senior researcher
MATSUHASHI Manabu, Researcher
Water Quality Control Department, Wastewater System Division（Key words）

Sewage system, Countermeasure of earthquake, Countermeasure of tsunami

1. Study committee for earthquake and tsunami
countermeasure techniques in sewage systems.
Tsunami and liquefaction in the Great east Japan
earthquake had brought critical damages to wastewater
treatment plants, pump stations in coastal areas as well as
sewer pipes including the inland areas throughout theTohoku and Kanto regions.
MLIT organized “Study committee for earthquake andtsunami countermeasure techniques in sewage system”
consisting of academic experts immediately after thedisaster. Then, they submitted four proposals and made asummary of committee as the last report on March 2012.
In this report, NILIM investigated the protection of
repeated damage and future tsunami-resistantcountermeasures in sewage system facilities. In addition,
we verified the efficiency of the earthquake-resistantcountermeasures adopted after the Niigata-Chuetsu
earthquake.
2. Checking the liquefaction countermeasure effect insewer pipes
Earthquake preventive countermeasure guideline insewage systems describes three backfill methods (such ascompaction of the backfilling soil, backfilling by crushedstone, and solidification of the backfilling soil) as theearthquake countermeasures of the sewage pipe. Among
those methods we checked the countermeasure effect of
the “backfilling by crushed stone” and “solidification of
the backfilling soil”. As a result, no traffic trouble of roadand no functional disorder of sewer flow were observedin any places that have executed such countermeasures(Photo 1). There found, however, a problem in terms of
construction management as the materials or strength ofsome sewer pipes has not fulfilled the given standard.

(A)

(B)

(C)

Photo 1. Situation of roads in the disaster area.
The road which had not provided earthquake-resistantcountermeasure (A). The road which had provided
earthquake-resistant countermeasure of backfilling bycrushed stone (B). The road which had provided
earthquake-resistant countermeasure of solidification ofthe backfilled soil (C).
3. The view of the sewage system design in considerationof tsunami protection measures.
We analyzed the characteristics of damage with the Great
east Japan earthquake and made a summary of the viewof the sewage system design for tsunami-resistantcountermeasures. Assuming the tsunami of theworst-case scenario defined by the prefecture and city
government, we summarized the functions to be
maintained on a priority basis on the tsunami hit by three
sections such as sewer pipes, pump stations andwastewater treatment plants as shown in Table 1. We
determined that the pumping for sewer evacuation andthe sterilization must be maintained even in the time ofdisaster. Functions to recover overall function weredivided into “Recover swiftly” and “Recover earlier”
based on the concept of the risk management.

Research Trends and Results
Table 1. Functions to be maintained at the time oftsunami
Type offacility
Functional
category

TsunamiresistanceType ofprotection

Sewer
Pump
Wastewater treatment plantsystem
stationEssential functions
Other functions
Backflow
Pumping Pumping
Sedimentation
prevention
Sterilization Dewatering“Must be maintained” even in adisaster situation

Risk avoidance

Other thanshown on left

Althoughfunctional
suspension isaccepted
temporary, it“should berecoveredswiftly”

Althoughtemporarysuspension isacceptable, it“should berecoveredearlier”

Risk reduction

Risk retention

4. Practical use of this research and future development
This study was summarized as four proposals as wellas the last report proposed by Study committee forearthquake and tsunami countermeasure techniques insewage systems, and effectively-utilized to recoversewage system facilities in damaged areas. Moreover,this study will benefit the revision of the Earthquake
preventive countermeasure guideline in sewage systemand the manual of earthquake-resistant countermeasure insewage systems.
【Reference】
1) Report of Study committee for earthquake and tsunami

countermeasure techniques in sewage systems
http://www.mlit.go.jp/mizukokudo/sewerage/crd_sewer
age_tk_000170-1.html