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spalling of the bottom flange of the deck. These displacementsrepresent the cumulative effect of both seismic events. Minorflexural cracking at the base of the central pier from transversemovement due to ground shaking was evident following theDarfield event, with minimal additional damage following theChristchurch event.▲ ▲ Figure 6. Settlement of approach material, exposure of rakedpiles, and cracking of the western abutment of South BrightonBridge. Note the rotation of the abutment in relation to the girderand cracking at rear of abutment seat.quake. Slumping of the material adjacent to the abutmentsdeveloped as a result of movement toward the river, whilethe approaches developed lateral spreading perpendicular tothe river (parallel to the sides of the approach embankment).Liquefaction ejecta was evident in the area surrounding theapproaches, with lateral spreading parallel to the river extendingto the north and south of the approaches on both sides.Similar damage occurred as a result of the Christchurch earthquake,with further severe lateral spreading.Lateral spreading due to both the Darfield andChristchurch earthquakes caused the east abutment to backrotateby approximately 7°, with spreading of the underlyingsoils exposing the abutment piles. The piles rotated along withthe abutment structure, with evidence of plastic hinge developmentin both the front and rear rows of piles. The gabionmat used for erosion protection in front of the abutments hadmoved away from the abutment as the underlying soil spread.These soil movements were larger than those observed in theDarfield event.The west abutment back-rotated by approximately 5° andlight cracking was observed on the tension face of the abutmentpiles after that event. The damage to the piles supporting thewest abutment caused by the Darfield earthquake was exacerbatedduring the February earthquake where the abutment hadback-rotated by an additional 3° for a total rotation of approximately8° (Figure 6) and plastic hinging was clearly visible onthe abutment piles. Soil beneath the abutment had settled significantly,exposing 80 cm of the supporting piles. Comparedto the post-Darfield conditions, there had also been a significantincrease in settlement and spreading at this abutment.Differential movement of the abutments relative to thebridge deck was evident, with the east abutment moving about22 cm along the line of skew to the north and settled about 3 to4.5 cm. The west abutment moved 20 cm along the line of skewto the south and settled 8.5 to 9.5 cm, with minor crushing andANZAC Drive BridgeANZAC Drive Bridge was constructed in 2000, runs in thenorth-south direction on State Highway 74 and spans theAvon River (Figure 2). Shown in Figure 4C, the bridge is atriple-span precast concrete girder structure (hollow core deck)that is supported by two four-column bents and concrete abutmentwalls with wingwalls. The south approach and abutmentwere constructed on an embankment fill, while the north endof the bridge was constructed at surrounding grade.The bridge site experienced marginal liquefaction andminor lateral spreading during the Darfield earthquake,but the bridge and its functionality were not affected by thisevent. However, the bridge was damaged by the Christchurchearthquake, yet remained functional after regrading theapproaches. Severe liquefaction, as evidenced by the large volumesof ejecta, and significant lateral spreading occurred inthe areas surrounding the north and south abutments duringthe latter earthquake, with evidence of liquefaction beingmore pronounced on the south end of the bridge. There werea significant number of sand boils and ejecta observed in thelow-lying areas adjacent to the embankment on the south end.Additionally, lateral spreading was observed on both the sidesof the embankment with the cracks running parallel to theroadway and having widths of about 8 to 18 cm. A short sectionof the south approach roadway was repaved and showed anabrupt elevation change due to ground settlement in the vicinityof the bridge abutment.Liquefaction and lateral spreading were less evident onthe north end of the bridge. However, a roundabout directlynorth of the approach possibly obscured some of the evidence.Cracking parallel to the river developed across the roadwayleading up to the north abutment and extended to both sidesof the bridge. The higher elevation of the area around the northapproach likely resulted in smaller volumes of liquefactionejecta as compared to the south approach area.The south abutment back-rotated 6°, as shown in Figure7, and lateral spreading at the base of the abutment resulted ina 30 to 40 cm gap between the concrete abutment and backfill.Also, a large horizontal gap formed between the abutmentand the edge of a walkway running along the riverbank, withthe bridge superstructure restraining the horizontal abutmentmovement. The rotation of the south abutment exposed a rowof steel H-piles supporting the abutment, which also appearedto have rotated along with the abutment. Numerous rubbertires were also exposed that had been placed between the abutmentand a walkway running along the riverbank. These tireswere designed to act as a lateral spreading buffer for the walkway.The north abutment showed similar rotational movementsbut had less rotation, of 3.5–4°. The lateral spreading along the956 Seismological Research Letters Volume 82, Number 6 November/December 2011