182 Damage as a Result of Problem Soils 1821 Liquefaction

One of the most common causes of damage to structures is the result of liquefaction to the surrounding soil. When loose saturated sands, silts, or gravel are shaken, the material consolidates, reducing the porosity and increasing pore water pressure. The ground settles, often unevenly, tilting and toppling structures that were formerly supported by the soil. During the 1955 Niigata, Japan, earthquake, several four-story apartment buildings toppled over due to liquefaction (Figure 18.4).

These buildings fell as the liquefied soil lost its ability to support them. As can be seen clearly in Figure 18.5, there was little damage to these buildings and it was reported that their collapse took place over several hours.

Partial liquefaction of the soil in Adapazari during the 1999 Kocaeli, Turkey, earthquake caused several buildings to settle or fall over. Figure 18.6 shows a building that settled as pore water was pushed to the surface, reducing the bearing capacity of the soil. Note that the weight of the building squeezed the weakened soil under the adjacent roadway. Another problem during liquefaction is that the increased pore pressure pushes quay walls, riverbanks, and the piers of bridges toward adjacent bodies of water, often dropping the end spans in the process.

The Shukugawa Bridge is a three-span, continuous, steel box girder superstructure with a concrete deck. The end spans are 87.5 m and the center span is 135 m. The superstructure is supported by steel, multicolumn bents with dropped-bent caps. It is part of a long elevated viaduct, and has expansion joints at Pier 131 and Pier 134. The columns are supported by steel piles embedded in reclaimed land along Osaka Bay.

During the 1995 Kobe, Japan, earthquake, increased pore pressure pushed the quay wall near the west end of the bridge toward the river, allowing the soil and westernmost pier (Pier 134) to move 1 m

FIGURE 18.4 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien; photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.)
FIGURE 18.5 Liquefaction caused building failure in Niigata, Japan. (Photo by Joseph Penzien; photo courtesy of Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley.)

eastward (Figure 18.7). This resulted in the girders falling off their bearings, damaging the expansion joint devices and making the bridge inaccessible. The easternmost pier (Pier 131) moved half a meter toward the river. It appears that the restrainers were the only thing that kept the superstructure at the expansion joint above Pier 134 together, preventing the collapse of the west span. The expansion joint had a 0.6-m vertical offset, and excavation showed that the piles at Pier 134 were also damaged due to the longitudinal movement.

Structures supported on liquefied soil topple, structures that retain liquefied soil are pushed forward, and structures buried in liquefied soil (like culverts and tunnels) float to the surface in the newly buoyant medium.

FIGURE 18.6 Settlement of building due to loss of bearing during the 1999 Kocaeli Earthquake.
FIGURE 18.7 Liquefaction caused bridge damage during the Kobe Earthquake.

The Webster and Posey Street Tube Crossings are 4500-ft-long tubes carrying two lanes of traffic under the Oakland, California, Estuary. The Posey Street Tube was built in the 1920s (Figure 18.8) while the Webster Street Tube was built in the 1960s (Figure 18.9). They are reinforced concrete (RC) tubes with a bituminous coating for waterproofing. The ground was excavated and each tube section was joined to the previously laid section. The tube descends to 70 ft below sea level.

During the 1989 Loma Prieta, California, earthquake, the soil surrounding the Webster and Posey Tubes (that carry traffic through the Oakland Estuary) liquefied. The tunnels began to float to the surface, breaking the joints between sections and slowly filling with water (Figure 18.10 and Figure 18.11).

0 0

Post a comment