A PROJECT OF REINFORCEMENT EMBANKMENT
FOR EARTHQUAKE RESISTANCE
OF THE MURAYAMA-SHIMO RESERVOIR,
AN EXISTING EARTH DAM
Bureau of Waterworks
Tokyo Metropolitan Government
We report that an example of an earthquake proofing measures on the Murayama-Shimo Fs=1.84 Fs=1.78
Reservoir, an existing earth dam. Fs=1.07
1.1 Outline of The Murayama-Shimo Reservoir
Location : The northwest part of Tokyo
Construction : Between 1916 and 1927
Total storage capacity : 12,148,000m3 Fig.4. Results of the Sliding Stability in the Case
Effective storage capacity : 11,843,000m3 of South-Kanto Epicentral Earthquake
Surface area at full-filed water : 1.1km2
Structure : zoned earth dam 0.9cm
Top lengths : 587.27m
Height : 32.6m
Photo.1. The Murayama-Shimo Reservoir
1：2 Fig.5. Prediction of the Volume of Residual Deformation
1：3.0 Core .0 counter weight fill
in the Case of South-Kanto Eepicentral Erthquake
Cut-off wall of water
Fig.1. Cross Section of Existing Dam Body 3. REINFORCEMENT SLOPE WITH GEO-TEXTILE
In case of normal time after completion, the sliding safety factor did not satisfy f =1.2 of
2. DESIGN OF REINFORCEMENT EMBANKMENT the aim, then reinforcement is necessary.
In January 1995, a gigantic earthquake M7.3 attacked Kobe-city. Soon we performed We decided to perform reinforcement with the geo-textile.
a seismic diagnosis for this earth dam. This diagnosis cleared that the embankment
would have damage at the time of an earthquake M7.0 class. 3.1 The Friction Characteristics of Geo-Textiles and Filling Materials
We use pulling test for setting the friction characteristics of geo-textiles and filling
2.1 Choice of the Earthquake to Examine materials.
Level 1 earthquake motion (That occurred once to twice in occupied term)
The occurrence probability 1/30 years, M7 class Lateral displacement
Level 2 earthquake motion ( The occurrence probability is very low) Air transducer
The occurrence probability 1/300 years, M8 class
100 Backfill soil
Table.1. The Assumed Input Earthquake Motions 100 Backfill soil
Level of Occurrence Assumption Acc Max Speed Max
Earthquake Probability Earthquake （gal） （kine） Load cell to measure
Level 1 1/30 years the pull-out load
Ansei-Edo Inland 6.9 186.3 11.1
1/300 years Trench 7.9 333.4 126.4
－ 7.1 458.2 147.1
Photo.2. Pulling Testing Machine Fig.6. Mechanism of Pulling Testing
3.2 Placement of Geo-Textile for Reinforcement Slop
The geo-textile is laid at the intervals of 1.6m in height for an anti-sliding failure
-400 South-Kanto epicentral earthquake
南関東地震 measures as a main.
0 5 10 15 20 25 30 35 40 The geo-textile is laid at the intervals of 0.4m in height for preventing surface
landslide as an assistance.
Fig.2. Example of the Earthquake Wave Pattern,
South-Kanto Epicentral Earthquake
2.2 Design of Reinforcement Dam Body TP.87.900
At first, designing a sectional structure by use a seismic coefficient method. The main reinforcement material 1:1.0
Then, confirming the earthquake proofing performance and the stability of the slope by TP.83.100
The main reinforcement material
use a dynamic analysis and a slope stability analysis. TA>=30.0kN/m,L=6.8m
Top of backfill TP.80.000
The main reinforcement material
Reinforcing structure TA>=36.0kN/m,L=6.8m TP.78.300
To be reinforced with filling on the downstream side.
The assistance reinforcement material Backfill
To install an inclined drain and a horizontal drain on the downstream side.
To be constructed in an acute angle of 45 degrees. TP.73.000
10.0m Counter-weight fill Fig.7. A Placement Example of Geo-Textile
Concrete blocks .5 1：2
1:1 .6 Geo-textile
drainage We have ensured a sufficiently high seismic stability of an existing earth dam.
Existing dam body
This project is the first case of reinforcing an existing earth dam by means of geo-
Fig.3. Cross Section of Designed Dam Body textile reinforcement.