What We Know

1
What We Know

• KOWACO has conducted a very comprehensive and
  thorough investigation. Their plan for the
  evaluation and selection of remediation is and
  appropriate for this dam
• Sink holes appeared soon after the
  reservoir was
• filled Apr. - Oct. 1998
• Considerable core material has been lost by
  erosion or dispersion on both upstream downstream
• left abutment area

2
What We Know (continued)

• Filter material has only limited contact with
  rock both upstream and downstream
• Foundation sand and gravel was left in place
  under the downstream position of the dam
• Foundation sand and gravel was left in place
  under the downstream position of the dam.

3
What We Know (continued)

• Recent exploration indicates zone of complete
  saturation, voids and granular material in the
  core.

4
What We Know (continued)

• Water samples taken from holes in the core show
  some turbidity.

5
What We Know (continued)

• While seepage is measured at the downstream toe,
  it is not possible to see where it is entering
  the drain

6
What We Know (continued)

• Water loss and voids encountered in the recent
  drilling along with tracer indicates the presence
  of damage to the core that continues to progress.

7
What We Know (continued)

• Exploration has conducted very loose material and
  voids exist in the core.
• All exploration stopped at the top of
  rock.

8
What We Know (continued)

• Presence of gravel layer support the occurrence
  of internal erosion.

9
What We Know (continued)

• Exploration shows gravely materials in depth
  30-45m, Sta.910 to 1210.

10
What We Know (continued)

• During construction considerable amounts of
  fill (15000 CM/day) were placed in the lower
  parts of the dam.
• Core continued over at one location.

11
What We Know (continued)

• Remediation by compaction grouting was
  successfully in the limited area. However the
  center core is in same state of dispersion and/or
  internal erosion. This is confirmed by the recent
  change in flow and turbidity in December 2002.