Philip Yong & Jiashun Yu, 4 Nov 2008
On Day 1 of the reconnaissance trip of the NZSEE team, we travelled from Chengdu and headed west towards the Epicentre areas in Wenchuan County. We passed through the city of Dujiangyan, where we observed structural damage to some of the older building stock, we plan to go back to Dujiangyan for a more detailed observation.
We arrived at the Zipingpu Dam site, a concrete lined rock filled dam height of 250m, and 650 m long. We were briefed by the Chief Engineer for the facility, and had a good grasp of the deformations that occurred as a result of the earthquake. Principal deformations and the behaviour of the dam recorded after the earthquake, were within acceptable limits. In short, the dam performed well. We also have the opportunity to see some slope stabilisation work being carried out following the quake. Reported acceleration at the base of the dam measured about 0.5-0.7g, with acceleration at the top as much as 1.7g.
We next travelled south through fairly mountaineous terrain towards Ying Xiu in Wenchuan County, the epicentre of the earthquake on 12 May 2008. It would have been impossible to get to this area from Chengdu after the quake, due to the extent of landslides and some of the damaged and collapsed bridge structures on the way. Our late timing for the trip to the area is a blessing as the roads have been re-established. This leg of the visit is astounding and from an earthquake engineering viewpoint, it covers all the areas that the NZSEE teams are there for. The experience, is both sobering and humbling in terms of the scale of the energy of the quake. Key observations:
- Massive landslides
- Large boulders dislodged from slopes from ground acceleration effects of earthquake
- Yin Xiu township totally wiped out
- Damages to a number of bridges, including total collapse of a bridge completed in 2004 on the road to Yin Xiu.
- Yin Xiu Primary School: major structural damage to buildings
- Massive land deformation at fault rupture
- 2 km long landslide debris, the scale of which just reinforce how powerful nature is
A sample of the pictures from today’s site visits are appended.
|Zipingpu Dam : Overall view downstream side||Zipingpu Dam : Deformation top of the dam downstream face|
|Epicenter at Ying Xiu : Rock came down from hillside in the quake||Yin Xiu Primary School : one of the many buildings severely damaged|
|Yin Xiu Primary School : one of a number of the buildings that collapsed||Court House right next to the fault rupture at Yin Xiu: collapsed floor|
|Bridge crossing a Ming Jiang Tributary: superstructure shifted 0.5m sideway by landslide at an abutment end||Yin Xiu Township : totally wiped out, many deaths still buried below rubble|
|Yin Xiu : Fault Rupture across a river||Yin Xiu Epicenter: 2 km long debris flow|
|Road to Yin Xiu : Collapsed Bai Hua bridge|
The team had a long and tough day, but what we had seen today totally justifies this reconnaissance mission.