In late January, the American Society of Civil Engineers sent three teams to the tsunami disaster zone to conduct damage assessments. Here are the second and third field reports from the Thai team.
One of the interesting observations today was that the first tsunami wave carried debris from the land out into the ocean. The second wave then drove the debrisalong with the wave energyinto various structures and lifelines. In addition, sand and rocks filled the sewage system, plugging the sewage pump stations. Control panels were damaged and cannot be easily replaced.
Coastal roads and associated retaining walls were eroded away, causing 10 to 15 ft of the road to wash away.
The local navy base suffered infrastructure damage. The tsunami wave hit with such force that 40 to 50 reinforced concrete poles were sheared off, cutting off power to the entire base, something rarely seen in earthquakes. This could indicate that debris impact creates excessive forces on structures. The emergency generators were flooded, which took the water treatment plant out of operation. A navy frigate broke free from the pier and has been aground for a month now.
Today we visited two fishing ports and a number of destroyed resort cities. Many lifelines were damaged, but not all are noteworthy for this summary.
We looked at eight bridges in the tsunami run-up zone. Most of the bridges were small two-lane, two- or three-span reinforced concrete bridges. Most bridges appeared to be less than 10 years old, while one or two were much older. There was no damage that would hinder the operation of the bridges.
One bridge had extensive erosion of its approach that washed out the road on both sides. It was fixed simply by filling the gap with compacted dirt. Most of the bridges sustained damage to their cast-in-place railings/K-rails; it appears as though debris thrown into the railings knocked them over. Inspection showed limited reinforcement ties to the deck, and that the reinforcement was sufficient to protect from lateral movement of the debris. All bridges inspected were suitable for operation, although the railings were not repaired, presenting a safety concern.
We inspected a number of elevated steel water towers in the inundation zone. All are slender column-type with a cylindrical tank at the top. Some towers were 40 to 60 feet tall. Steel risers (support columns) were 4 to 6 feet in diameter. In many cases the footings were exposed by erosion, but posed no threat for overturning. In one case, there were numerous marks on the riser column indicating contact with debris, but the debris did not affect the operation of the tanks. Most tanks were out of service since appurtenant piping was gone and the village was deserted, reducing the need to restore service.
There was also one damaged cellular communications towera four-footing, lattice-type steel tower, roughly 60 ft tall, with the cellular panels mounted at the top. There was extensive erosion around the main tower foundations, but the foundations were not compromised. However, the cables were supported by a small structure whose foundation was eroded away, causing complete failure. The tower was still out of service on Feb. 2.
BEACHES AND RESORT
Khao Lak, a new upscale resort area north of Phuket, was completely devasted by a 10-meter-high wave. Resort infrastructure was almost completely destroyed. All hotels are closed for extensive repair. Foundations were scoured, walls collapsed by wave pressure, and roof tiles removed by wave impact. Damage was severe to both first- and second-floor apartments. Nonetheless, the beach, which was severely eroded by the tsunami, is recovering rapidly in this area. At least 100 feet of beach has been accreted naturally since Dec. 26. Many damaged hotels are now being demolished; others stand like ghost towns. A fishing portBan Nam Ken, north of Khao Laksuffered extensive damage to concrete piers, and nearly all of the fishing fleet was either destroyed in place or washed a kilometer inland.