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Retaining Walls Damaged in the Chi-Chi Earthquake

Retaining Walls Damaged in the Chi-Chi Earthquake. Y.S. Fang, Y.C. Yang, and T.J. Chen Presented by: Amanda Luksetich Spring 2005. Introduction. September 21, 1999 at 1:47 am Earthquake of magnitude 7.3 on the Richter Scale Near the town Chi-Chi in Taiwan, “Chi-Chi Earthquake”

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Retaining Walls Damaged in the Chi-Chi Earthquake

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  1. Retaining Walls Damaged in the Chi-Chi Earthquake Y.S. Fang, Y.C. Yang, and T.J. Chen Presented by: Amanda Luksetich Spring 2005

  2. Introduction • September 21, 1999 at 1:47 am • Earthquake of magnitude 7.3 on the Richter Scale • Near the town Chi-Chi in Taiwan, “Chi-Chi Earthquake” • 49,542 dwellings completely destroyed • 42,746 dwellings partially damaged • 2,432 people killed, 46 still missing

  3. Chi-Chi Earthquake

  4. Chi-Chi Earthquake • Shaking frequency 1.0-4.0 Hz • Focal depth 8 km • Rupture along Che-Lung Pu fault was 105 km

  5. Seismic Behavior of Gravity Walls • 3 retaining wall failures investigated • Base of wall lacks resistance to dynamic thrust – active wall movement occurs • Wall gradually moves away from backfill • Soil wedge slides along failure plane • Causes tension cracks and settlement in backfill

  6. Site 1 - Introduction • Taiwan Provincial Highway 14 • Built to retain steep excavation for highway construction • Concrete placed in 5 pours • No special treatment provided at construction joints

  7. Site 1 – Failure Analysis • Top layers moved away from backfill along construction joints • Top 2 blocks fell to side ditch • 20 m damage zone • Suspect frictional resistance not adequate at top of wall

  8. Site 1 – Failure Analysis • FS overturning > FS sliding • Sliding failure occurred along construction joint • FS decreases with increasing horizontal ground acceleration • Static FS acceptable • FS < 1 when Kh = 0.24g • Peak Kh observed to be 0.38g and 0.47g • Wall may have moved some with each effective cycle of ground shaking

  9. Site 1 – Failure Analysis • Soil properties influence analysis results • FS increases with increasing friction angle • 20 m failure segment • Locally poor compaction • Weaker soil present • Design Kh only 0.23g • Kh measured up to 0.47g and 0.79g

  10. Site 1 – Recommendations • Wall repaired in 2 months • Shearing reinforcements at construction joints • H-piles to resist potential movement of steep slope • Shearing key to prevent sliding failure along joint (recommended)

  11. Site 2 – Introduction • Provincial Hwy 21 near Sun-Moon Lake • Retain steep slope for highway construction • Close to epicenter • Lateral movement observed • Active soil wedge collapsed, but most of body wall undamaged • 40 km damage zone

  12. Site 2 – Failure Analysis

  13. Site 2 • Unexpected strong ground motion (close to epicenter) • FS against sliding is 1.15 (static), 1.5 required • Short, thick wall should resist overturning well • Bearing capacity failure may occur under seismic load • Settlement will occur if qmax exceeds qult, result in overturning

  14. Site 2 – Failure Analysis • Kh recorded as 0.59g at nearby station • FS bearing capacity slightly less than FS sliding • Overturning wall most likely result of insufficient bearing capacity under the toe Recommendation: Do not neglect stability check for bearing capacity failure

  15. Site 3 – Introduction • Taiwan Cinema Culture Town • Constructed above the Che-Lung Pu fault line • Vertical and horizontal displacements of 2.0 m and 1.3 m, respectively • Body of wall unbroken • Buildings on top of backfill severely damaged • Deformation • Strong ground shaking

  16. Site 3 – Failure Analysis

  17. Site 3 – Failure Analysis • Vertical displacement uplifted backfill, caused overturning • Horizontal displacement caused sliding failure and heave in front of toe • Kh recorded as 0.79g • FS acceptable for static conditions Recommendation: Do not build on or near any active fault lines!!!

  18. Questions?

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