Earth structures and slopes on roads

Geology Research Team Soil Mechanics and Dynamics Research Team Construction Technology Research Team

Geology and Geotechnical Engineering Research Group Public Works Research Institute

(Map by Geospatial Information Authority of Japan)

Iwate Pref.Akita Pref.

Miyagi Pref.Yamagata Pref.

Niigata Pref.

Fukushima Pref.Kamikamato, Iwaki City (5.)

Tamachi, Yabuki Town (3.)

Fushiogami, Fukushima City (2.)

Narita, Ishinomaki City (4.)

Tofugaura, Noda Village (6. Photo 23-29)

Shizugawa(Photo 33), Kamidaibou(Photo 34),Minamisanriku Town (7.)

Kurauchi(Photo 30(a)), Koizumi(Photo 30(b)(c)),Kesennuma City (6.)

Koganezawa, Kesennuma City(7. Photo 31,32)

Fig.1 Location map of damaged sites mentioned

N

1. Summary

Damage to earth structures and slopes on roads is minor, in general, but there are some characteristic cases like the following pages. Damage was mainly caused by the main shock and tsunami on 11th March, and an aftershock on 11th April. Main types of damage are collapse of embankment filling up the valley, settlement of embankment on the soft ground, collapse of the loosened slope, landslide on the slope of Neogene rocks, and damage to embankments and slope protection works by tsunami. Retaining walls were not damaged without damage of back filling soil.

2. Collapse of the embankment filling up the valley close to the national road

Collapse volume : about 11,000m3Collapse was caused by the main shock on 11th March, and closed the national road. The embankment was developed as a residential area by private company about 40 years ago. The embankment fills up the valley. Filling material mainly consists of excavated soil of pyroclastic deposits.

Photo 1 Collapse of the embankment of residential area constructed filling up the valley close to the national road

Photo 5

Photo 2

Photo 4

National road

Photo 2 Upper part of the collapse Photo 3 Head of the collapse

Photo 4 Middle part of the collapse and moved road surface Photo 5 Toe of the collapse covering the national road(Photo by Fukushima Office of River and National Highway, MLIT)

Photo 3

3. Damage of the embankment of the prefectural road on the soft ground

Damage was caused by the main shock on 11th March. Settlement of the embankment occurred, and many cracks appeared on the top of the embankment (road surface). The foundation ground of the embankment was soft ground consisting of clayey soil (about 3 in N-value and 15m in thickness). Cracks also appeared on the foundation ground.

Photo 6 Settlement in the embankment of theprefectural road (red arrows)

Photo 7 Cracks on the foundation ground of theembankment (red arrows)

Photo 8 Cracks on the road embankment

4. Collapse of the loosened slope on the national road

Collapse volume : unknown (because depth is unknown)Collapse was caused by the main shock on 11th March, and collapsed again 3 days after the main shock. The geology of the slope is Triassic slate. Deep loosening of the slope is estimated from the aerial photographic interpretation result and boring.

Photo 9 Damage of the national road by slope failureRed broken line : collapsed area by the earthquake Red dotted line : scarp in the upper slope

(Photo by Sendai Office of River and National Highway, MLIT)

Photo 12

Photo 14

Photo 13

Boring point (above the slope)

Photo 10, 11

(Photo by Sendai Office of River and National Highway, MLIT) (Photo by Sendai Office of River and National Highway, MLIT)Photo 10 Disaster site about 10 hours after the main shock Photo 11 Disaster site about 3 days after the main shock

Photo 12 Scarp in the upper slope (between red arrows) Photo 13 Deformed slopeRed arrows : cracks in the slope

Photo 15 Core obtained from a borehole above the collapsed slope

0 12m : Core is well weathered and yellow/brown in color. Many cracks and clay filling cracks are observed.Bellow 12m : Core is relatively hard and grayish in color. Many cracks and clay filling cracks are also observed.

depth(m) depth(m)

(Photo by Sendai Office of River and National Highway, MLIT)

Photo 14 Left side of the toe

Fig.2 Aerial photographic interpretation map of surrounding slope

(Photo by Geospatial Information Authority of Japan)

5. Damage of the prefectural road by landslide

Landside volume : unknown (because depth is unknown)Landslide was caused by the aftershock on 11th April, and closed the prefectural road. The geology is Neogene tuffaceous sedimentary rocks.Ground anchor works measured on the cut slope (toe of the landslide) were damaged.

Photo 16 Damage of the prefectural road by landslideRed broken line : landslide area occurred by the earthquake

Photo 17

Photo 18, 19

Photo 22

Photo 21

Blue arrow : direction of the landslide movement

(Photo by Fukushima Pref.)

Photo 20

Photo 17 Left side of the toe Photo 18 Uplift of the road surface at the toe

Photo 19 Damaged ground anchor works Photo 20 Right side of the toe

Photo 21 Cracks in the landslide Photo 22 Head of the landslide

Depression zone

Landslide body

6. Damage of the slope protection works on the national road by tsunami

There were some cases of damage to slope protection works caused by the tsunami after main shock on 11th March. One case is damage of concrete frame (precast concrete frame and cast-in-place concrete frame) as follows. Precast concrete frame : Stones inside the frame and soil back of the frame were washed away. The frame members were also washed away partially. Cast-in-place concrete frame : Shotcrete inside the frame and soil back of the frame were washed away. The frame members were broken at many points. Another case is stripping of shotcrete on the slope.

Photo 23 The site of damage of slope protection works(precast concrete frame) by tsunami

Photo 24 Damage of precast concrete frame

Photo 25 Opening back of the precast concrete frame by the washout of soil

Photo 25Photo 24

Photo 27

Photo 29

Photo 28

Photo 28 Damage of the concrete frame member

Photo 26 The site of damage of slope protection works(cast-in-place concrete frame) by tsunami

Photo 27 Damage of concrete frame

Photo 29 Damage of the concrete frame member

Photo 30 Stripping of the shotcrete on the cut slope on road in the area struck by tsunami

(a) (b)

(c)

Tsunami reached over the top of the shotcrete in every case of (a)-(c).

7. Embankments and retaining walls in the area struck by tsunami

Various scales of damage to embankments were caused by the tsunami after the main shock on 11th March. There was a case of the loss of the retaining wall in case that the embankment back of the retaining wall was damaged. No damage of retaining wall was observed, unless the back filling soil was damaged.

Photo 31 Damage of the embankment by tsunami Photo 32 Damage of the embankment by tsunamiRetaining wall at the foot of the embankment was lost in the part where embankment was damaged.

Photo 33 Concrete block retaining wall on the cut slope in the area struck by tsunami

Photo 34 Concrete block retaining wall on the road embankment in the area struck by tsunami

Tsunami reached over the top of the retaining wall, but no damage of the retaining wall was observed.

Tsunami reached over the road surface, but no damage of the retaining wall was observed.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23