| Abstract |
The 105 Mahiao landslide area lies within the downthrown block of Mahiao Graben of the Leyte Geothermal Production Field (LGPF). The geologic feature is traversed by the Central Fault Line, a major bifurcate of the Philippine Fault that traverses the geothermal field. Ground cracks and differential movements were recorded since 1996, after which engineering mitigating measures were implemented to avert the landslides which could potentially damage EDC geothermal facilities such as pipelines, injection wells, separator vessels, and also cause widespread flooding by damming of Mahiao River. Temporary road repairs, concrete lining of canals, refilling of cracks and construction of concreted reinforced masonry walls and benching were undertaken to reduce the potential massive landslide estimated at ~800,000 m3. In February 2006, coincident with the Guinsaugon landslide of Southern Leyte, ground bulges, massive cracks and other manifestations of ground deformation in 105 Mahiao led to re-evaluation of the area. To address the landslide hazard which could potentially cost EDC of approximately $87,000 per day in revenue loss from power outage alone, massive slope benching to remove 123,000 m3 of mass and subsequent vegetative restoration program were instituted. Further geotechnical investigations were also conducted and water-level monitoring wells were installed in the area to continuously monitor the effectiveness of the new mitigating measures. No new cracks, bulges and manifestations of ground movements were documented to date, attesting to the effectiveness of the mitigating measures implemented. |