Research Trends and Results

Case Studies and Dynamic Centrifuge Tests to Evaluate
Earthquake Related Damage of Special Levees of Rivers
KAJIO Tatsushi, Researcher; KATAOKA Shojiro, D.Eng, Senior Researcher; KANEKO Masahiro, HeadEarthquake Disaster Prevention Division, Research Center for Disaster Management
Keywords: special levee of river, liquefaction, dynamic centrifuge tests, seismic retrofit

80(cm)
displacement (Max value)
Horizontal
水平変位量（最大値）（cm）

Damage to retaining
擁壁被災ありwall

70

No damage to擁壁被災なし
retaining wall
Damage to sheet
矢板被災ありpile

60

No damage to sheet

矢板被災なしpile5040302010002468Liquefaction(m)
液状化層厚layer（ｍ）

1012Figure 1: Relation between Horizontal
Displacement in Frame and Thickness ofLiquefaction Layer in Damage Cases
Unit: m (model dimension: mm)
単位：ｍ（模型寸法:mm）75（1 500）

1010（200）（200）

37.5（750）

5（100） （100）1012.510(200)

（200）

（250）

5（250）

5■■■

背面土（非液状化層）Dr=85%
Back soil (non-liquefactionlayer) Dr = 85%■▲■▲

Liquefaction layer

■▲

■

▲

▲

■
◆◆■■■
◆◆■▲

■▲

▲

20▲

■■
◆■
◆■
◆◆■■▲▲

5.44■▲Dr = 55%

液状化層Dr=55%6■■◆◆◆◆■■■（120）■▲（108） （80）

（142）

■
▲

9.4（188）

7.125

■
■

（100）

（750）

12.5

Non-liquefaction layer
非液状化層Dr=90%（400）

37.5（500）

1. Introduction
For a river levee, a soil embankment is in principle
constructed. In some cases, however, special levees(Independent type structure: Concrete retaining wall[“retaining wall”]), steel sheet pile ["sheet pile"], or
parapet structure) are constructed due to land conditions,etc. Most of these special levees have a complicatedstructure due to extension / alteration works, etc. Sincesuch special levees are expected to demonstratecomplicated behavior during an earthquake, it is required
to implement advanced earthquake-proof diagnoses andmeasures. Thus, considering that the first step to solve
this issue is to understand their behavior during anearthquake, we collected data on the cases of damage of
special levees in order to analyze the causes andconducted dynamic centrifuge tests to clarify the damage
mechanisms.
2. Case study on the condition of special levees andseismic damage
The special levees in the river sections under the direct
administration of MLIT (209 locations, about 190 km intotal) are mostly composed of parapet structures (approx.
80%), followed by retaining walls (approx. 20%), andsheet piles (less than 10%). Moreover, about 70% ofthem are concentrated in the three major metropolitan
areas, so it is important to ensure earthquake resistance.
Twenty nine damage cases on special levees located in
the sections under the administration of MLIT,
prefectural control, etc., were compiled. It was observedthat major damage occurred where the thickness of theliquefaction layer was more than approx. 3 m for theretaining walls and more than approx. 2 m for the sheet
piles, as shown in Fig.1.,which shows the relationshipbetween displacement and the liquefaction layer during
an earthquake. Thus, the liquefaction layer is considered
to be the main cause of damage.
3. Implementation of centrifuge tests
Model tests were conducted by setting a 1:50 scalemodel (Fig. 2) on the dynamic centrifuge of thecooperating Public Works Research Institute (PWRI) andsubjecting it to excitation under centrifugal accelerationof 50 G. In these tests, the thickness of liquefaction
layer was changed to 3 types for both retaining walls andsheet piles.
The mechanism of damage of special levees was
identified from the centrifuge tests. The pore waterpressure of the liquefaction layer increased underexcitation, following which the ground lost the effective
stress and was liquefied, causing flow force to be directedto the frame. The flow force made the balance of applied
force unstable, consequently causing horizontal/verticaldisplacement and/or rotation (tilt) of the frame. Inaddition, the displacement of the retaining walls and thesheet piles showed the same tendency as the compiled
damage case: horizontal displacement increased as theDr = 90%▲▲■
Earth pressure gauge (21■ Strain gauge (12 sheets)
◆pcs)

■
■

加速度計(20個）
土圧計(21個) ひずみゲージ(12枚)
間隙水圧計(20個) ■Accelerometer(20 pcs)
変位計（ﾚｰｻﾞｰ）(2個)
変位計（ﾎﾟﾃﾝｼｮﾝﾒｰﾀｰ＋ｱﾙﾐ板）(6個)Displacementgauge (laser) (2 pcs)

▲ Pore pressure meter (20 pcs)

Displacement gauge (Potention meter + Aluminum board) (6 pcs)

Figure 2: Schematic Diagram of the Model (Casewhere the liquefaction layer is 7.1 m below the riverbed.)liquefaction layer became thicker, and verticaldisplacement was minimal in the cases where thefoundation of the retaining walls and the sheet piles were
supported by the non-liquefaction layer.
4. Future study
We plan to study seismic retrofit methods using
two-dimensional static analysis and promote studies thatwill resultantly propose effective seismic retrofit methods
by implementing model tests .