3rd JSPS-DOST International Symposium on Environmental Engineering

Geotechnical Hazards and Geotechnical Hazards and Disaster Mitigation TechnologiesDisaster Mitigation Technologies

J. Kuwano, M. Warakorn, M. Zarco and M. Adajar

Natural hazard is unexpected or uncontrollable natural event of unusual magnitude that threatens the activities of people or people themselves (Orense, 2003)

Geotechnical hazards are natural events which directly affect the ground or caused ground movements.

- Earthquakes and earthquake related hazards like soil liquifaction, lateralspreading and tsunami

- Landslides or slope failuresOrense, RP (2003) “Geotechnical Hazards-nature, assessment and mitigation”

Human activities can increase the occurrence and severity of geotechnical hazard

- building on top of unstable slope will increase the possibility of slope collapsing.

- steepened slopes due to cutting into a hillside or embankment may initiate landslides

- too much logging operations

EM-DAT Emergency Disasters Database www.em-dat.net

Earthquake related hazards

The 1983 Nihon-kai chubu Earthquake

Roads in Wakami town in Akita Prefecture was totally destroyed

The 1983 Nihon-kai chubu Earthquake

Sand volcano appeared as evidence of soil liquefaction

1995 Hyogo-ken Nanbu (Kobe) Earthquake

Damage on the building is concentrated at a particular story due to building’s vertical irregularities

1995 Hyogo-ken Nanbu (Kobe) Earthquake

The 18-span bridge of Kobe Line in the Hanshin Metropolitan Expressway

The 2004 Chuetsu Earthquake

Derailed Japanese bullet train (Shinkansen)

The 2004 Chuetsu Earthquake

Lifted manhole at Nagaoka City as a result of soil liquefaction

The 1990 Luzon Earthquake

Before the earthquake

After the earthquake

The 12-storey section of Hyatt Hotel collapsed over the lobby

The 1990 Luzon Earthquake

Building in Dagupan City sink by as much as 1 meter

The 2004 Indian Ocean Earthquake (Asian Tsunami)

The aftermath of tsunami disaster in Thailand

Landslides related hazards in the Philippines

The Cherry Hills Landslides

The Cherry Hills Subdivision in Antipolo City. Photo by Punongbayan (1999).

The Panaon Island Landslides

The landslides on the left buried the village in Punta, San Franscisco, Panaon Island, Southern Leyte killing hundreds of people Photo by the Philippine Star (2003)

The Quezon Landslides

Numerous landslides on forested areas and flooded areas along Gumian River, Quezon Province

The Mayana, Jagna Lanslide

The source area of the Mayana landslide in Bohol Island

The Guinsaugon Landslide

The catastrophic rock-slide avalanche buried the entire village of Guinsaugon in St. Bernard Southern Leyte

Mitigation Techniques

Mitigation measures that can be adopted to reduce risk :

• Risk evaluation and risk communication

- preparation of zoning map

• Risk monitoring to provide timely warnings through media such as TV and radio broadcasting

Liquefaction hazard mitigation techniques :

• Soil improvement and densification -sand compaction pile, vibroflotation, dynamic compaction, compaction grouting

• Increase the drainage ability of the soil

• Ground deformation control - sheet pile wall, soil cement column wall

Studies on mitigation techniques on soil liquefaction:

• Dungca, J.R. (2006) Effects of laterally spreading liquefied ground on single and double piles.

• Honda, T. et.al (2005) Mitigation techniques of damages of quay wall due seismic liquefaction

Slope protection and stabilization techniques

CONTROL WORKS:

• Soil removal or unloading - removing materials from the upper part of the slope, removing loose and unstable materials to reduce the driving force on the slope and to balance the failure.

• Benching - is the practice of transforming one high slope into a series of lower slopes with horizontal surfaces in between slopes.

Benching of slopes in Tongonan, Leyte

• Installing proper drainage

Slope stabilization using sub-horizontal drains

• Slope protection – use of grouted riprap, gabion walls, mortar spraying, and vegetation

Rounded, cobble and boulder-sized rocks are used as rip-rap wall for slope protection of roads.

Application of gabion walls in the Philippines

Mature vetiver grass in road projects

The Vetiver grass and its excavated roots

PREVENTION WORKS :

• Soil nailing and rock anchoring

Soil nailing and rock bolting used in construction of the buildings

• Rockfall barriers and rockslide shelters

Rockslide shelter and barrier along the highway leading to Baguio City, Philippines

Thank you !