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(A)(C)(B)▲▲Figure 5. Ferrymead Bridge field investigation data: A) shearwave velocity (V s ) profile; B) liquefaction assessment using V sdata, comparing the cyclic resistance ratio CRR 7.5 for the site tothe Darfield (CSR 7.5 DAR) and Christchurch (CSR 7.5 CHC) cyclicstress ratios. C) Damage to western abutment and temporarystabilization works.axis. The lateral spreading caused permanent rotation andcracking of the abutments and a number of the piers. Extensiveflexural cracking was evident at the base of the piers at theirconnection to the pile cap. The rear section of the east abutmentback-rotated 2.5° and the section supporting the bridgedeck back-rotated 5°. Additionally, surveys showed the eastabutment moved vertically upward 10 cm, but there was negligiblemovement of the eastern pier.Approximately 8-cm-wide lateral cracks were observedin the vicinity of the drilled shaft supporting the new girder,with the cracks running in both the longitudinal and transversedirections. This caused the top of the new concrete bridgegirder to rotate about 2° toward the river and caused approximately30 cm of ground settlement, measured relative to thebottom surface of the new girder, which was originally cast ongrade.Severe liquefaction, as evidenced by significant volumes ofejecta, and lateral spreading occurred in the area leading up tothe west abutment. Surveys showed that the west abutment andpier had settled 20 cm and shifted horizontally 20 cm towardthe river. The soil in front of the abutment settled approximately80 cm, but no appreciable rotation of the abutment wasobserved. The foundations supporting the west bridge pier inFigure 5C had shifted to the east, causing the support columnsto be out of plumb. Remedial efforts have been completed totie back the foundations supporting the western pier that experiencedsignificant tilting to the west abutment using highstrengthsteel rods.Following the Christchurch event, Spectral Analysis ofSurface Waves (SASW) was performed at a location 60 m tothe west of the west abutment. The shear wave velocity (V s ) profilefor the west end of the bridge is shown in Figure 5A. The V sprofile shows a soft soil layer between 1.5 and 4 m depth, overlyinga much stiffer layer, and the water table at 1.75 m depth.Using the PGAs listed in Table 1, the cyclic stress ratios (CSRs)for both the Darfield and Christchurch earthquakes were calculatedfollowing the methodology outlined in Youd et al.(2001). The magnitude scaling factors (MSF) recommended byAndrus and Stokoe (2000) were used to scale the CSRs to anM w 7.5 event (i.e., CSR 7.5 ). Using the shear wave velocity datashown in Figure 5A, the cyclic resistance ratio (CRR 7.5 ) for theprofile was calculated following the Andrus and Stokoe (2000)procedure, also outlined in Youd et al. (2001). The overburdencorrection factor, K σ , was further used to modify the CRR 7.5values (Hynes and Olsen 1999). This method allows for thedirect comparison of the CSR 7.5 induced by the two earthquakeswith the CRR 7.5 for the profile, as shown in Figure 5B.As may be observed from this figure, liquefaction is predictedto have occurred from ~1.5 to 4 m during both the Darfield andChristchurch earthquakes (i.e., CSR 7.5 > CRR 7.5 ), with thefactor of safety against liquefaction being significantly lowerduring the Christchurch event. While evidence of severe liquefactionwas observed following the Christchurch earthquake,no liquefaction was evident following the Darfield earthquake.South Brighton BridgeThe South Brighton Bridge (Figure 4B) was constructed in1980, runs in the east-west direction, and spans the Avon Riverjust north of where the river empties into the Avon-Heathcoteestuary (Figure 2). The bridge is a three-span skewed reinforcedconcrete structure with seat-type abutments on rubberbearings and single piers, all of which are supported by rakedoctagonal precast, prestressed concrete piles. The abutmentrubber bearings were removed due to the permanent movementsthat developed during the Darfield earthquake (Palermoet al. 2010) and were replaced with temporary hardwood packers.The bridge site was a wide wetland prior to the bridgeconstruction. To construct the bridge, two approach embankmentsapproximately 4 m in height were extended out into thewetlands, with the bridge structure spanning the river channel.These embankments were constructed of uncontrolled fillmaterial.Significant cracking of the approach embankments onboth sides of the bridge occurred during the Darfield earth-Seismological Research Letters Volume 82, Number 6 November/December 2011 955