Many roads in Christchurch, New Zealand, suffered damage due to the high magnitude vertical and horizontal shocks and aftershocks created by the 2011 earthquake. Typical of this was Fitzgerald Avenue, which borders the River Avon and developed a 200 metre long by two metre deep rent. This required complete reconstruction to restore the 38,000 vehicles a day traffic flow, as well as to be made more resistant to future damage.
River banks offer excellent locations for access for roads around much of Christchurch, but the typical weak river silts have poor load bearing characteristics. In this earthquake prone area, seismic movement in the 2011 quakes caused lateral spread of the underlying soil layers towards the rivers, causing sheer damage in road construction. This was the failure mechanism at Fitzgerald AvenueMany roads in Christchurch, New Zealand, suffered damage due to the high magnitude vertical and horizontal shocks and aftershocks created by the 2011 earthquake. Typical of this was Fitzgerald #
Deep foundations to reach load bearing layers for improved roadway support would be costly to construct and take a long time to complete, with consequent prolonged disruption to traffic. Additionally, non-stabilised construction methods may not provide the optimum solution where high energy ground movement occurs.
Consulting engineers Opus International observed that a section of riverside roadway located less than 3km away, had been built on very similar underlying soils. Despite being subject to the same cycle of extreme seismic activity, it had survived with no visible signs of damage.
The 20 year old road construction comprises an earth embankment, with the soil mass reinforced by Tensar uniaxial geogrids fastened to a retaining wall comprising precast concrete panels. A similar design was therefore adopted for reconstructing the roadway at Fitzgerald Avenue. Stone columns were inserted into the silt foundation, over which was placed a reinforced soil mass of well graded and compacted mineral aggregate layered with lengths of Tensar uniaxial geogrid. This was faced with precast concrete facing panels which incorporated cast-in short lengths of geogrid; the short lengths were fastened with a simple bodkin joint to the geogrid layers in the soil mass.
The resultant, 3.2m high, near vertical wall allowed restoration of the full width of the road and the addition of pedestrian and cycle access.
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