1. Reservoir bank slope in Laxiwa
Hydropower Station, China
Dexuan ZHANG, Gonghui WANG
Shanghai Jiao Tong University, China
DPRI, Kyoto University, Japan

2. Laxiwa Hydropower Station
Laxiwa dam: a hydropower station on the upper reach of
Yellow River. Guide County, Qinghai province, 134 km far
from Xining, captical city of Qinghai Province

3. Laxiwa Dam: 2nd cascade hydropower
Height: 250 m
Crest length: 460 m
Capacity :1.08 billion m3
Active capacity: 0.15 billion m3
Power Generation:
(6×70)4.20 Million kW

4. Laxiwa Dam

5. Guopu unstable slope
Oct. 2001: Construction started
Mach 2009: Impundement
May 2009: Power generation
July 2009: slope deformation started
Scale of the unstable slope:
Height: 700m; Width: 1000m; Volume: 70 M m3

6. 500m
700m
2452m
2254m
50°

7. Topography and Geology

8. Deformation on the head cliff

9. Deformation on the slope
1989
March 2010
May 2013

10. Slope deformation by remote sensing
１．interferometric synthetic aperture radar (INSAR）
ALOS PALSAR image list
2. Optical imagery
ALOS PRISM image list

11. Results from INSAR Analysis
Before impoundment:
Nov. 9, 2007-June 10, 2008
< error (10cm)
After impoundment:
2009-12-14～2010-01-29
2009-12-31～2010-02-15
Coherence: low
a: 2007-12-09～2008-01-24
b:2008-01-24～2008-03-10
c:2008-03-10～ 2008-06-10

12. Optical imagery analysis (ALOS PRISM)
 Imageries at two differing periods were processed
 In case of no/small deformation, change in the gray value of the processed image
will be very small.
 The area where deformation occurred will show blue or yellow color in different
phases
Before impoundment:
2007-11-14～2008-07-01
No change in gray value
No deformation > 2.5 m

13. Optical imagery analysis (ALOS PRISM)
After Impoundment:
2008-07-01（before)
~2009-04-03（after)
No change in gray value
No/small deformation

14. Deformation after impoundment
2009-04-03 ~ 2010-05-22
Most part of the slope are in gray color
Max displacement: 3 pixels, 3×2.5ｍ=7.5ｍ

15. View from Google Earth

16. Summary
InSAR data: Deformation before the impoundment was very
small.
ALOS PRISM: No obvious deformation during the period from
November 2007 to April 2009. Deformation with the horizontal
displacement up to 7.5 m occurred during the period from April
2009 to May 2010.
The response of sliding to the increasing water lever suggests
that the sliding surface may be locating near the river bed. The
cracks occurring on the terrace crest of the slope and the
continuing deformation reveals that the slope may not be
sliding as a whole.

17. What is
happening
now?

18. Landsliding monitoring

19. Landsliding monitoring

20. Countermeasures now
Surficial displacement monitoring system:
GPS + standard survey

21. 290m
750
m

22. Deforming
on the
upper
surface

23. Countermeasures now
Inside the deforming mass
Survey tunnel + Vertical boring and monitoring

24. Sliding surface inside the tunnel

25. What is happening now?

26. What we are doing now
Seismometers

27. What we are doing now
Shear behavior of the sliding surface
Samples

28. Thanks