Inspire : Public Works July Aug 2013
36 Public Works Professional July-August 2013 When the notorious earthquakes struck Christchurch, New Zealand, in 2010 and 2011, Fulton Hogan was briefed by the Stronger Canterbury Infrastructure Rebuild Team (SCIRT) to investigate the performance of various pavement structures during the event. "The aim was to assess which pavement types would provide optimum performance in future seismic events," says Dr Bryan Pidwerbesky, General Manager, Technical at Fulton Hogan. "Inspection showed most pavements had performed well and that most damage was caused by liquefaction beneath the surface," he says. "This erupted through weak spots, eroding and undercutting the surrounding pavement, resulting in sink holes, and di erential subsidence". MOST PERFORMED WELL In most cases the actual pavement performed well, according to Pidwerbesky, with liquefaction rupturing the pavement, forming holes and large cracks but leaving the pavement layers more or less intact between the breakage points. The investigation found that foamed bitumen stabilised (FBS) pavements performed particularly well. On streets where there were unbound granular pavements adjacent to an FBS section, the latter was less a ected by liquefaction. At sites where fabric was used in the pavement construction, less liquefaction was found throughout than on adjacent sites without fabric. An issue identi ed with fabric performance was the leakage of liquefaction through the fabric joints. The main observation from the investigation was that the use of bound materials and fabric in pavement reconstruction should minimise the contamination of the pavement materials and build some resilience into the reconstructed pavements. However, their use would not prevent liquefaction from occurring or rising. The added pavement resilience would help protect the materials so they could be recycled or reused in the event of another earthquake. However, the fabric might prevent future stabilisation and prove only to be a one-o protection. Once modi ed, the materials might not be suitable for further modi cation. GRANULAR ALSO RESILIENT The investigation also found that the aggregate in unbound granular pavements could be contaminated with up to 30% liquefaction material without adversely a ecting its performance. Moreover, a thicker, sti structural asphalt and concrete pavement could in theory constrain the upward movement of liquefaction material, but no evidence was found to support this concept. Instead, liquefaction was o en trapped under asphalt, and created bulges. The only feasible approach to repairing these bulges was to remove the asphalt and the underlying material, and replace it with new construction. Pidwerbesky will elaborate on the ndings at the upcoming IPWEA International Conference in Darwin. ••• PAVEMENT PERFORMANCE DURING AN EARTHQUAKE WHEN ROADS ERUPT A high-magnitude earthquake can affect different pavements in different ways, as an investigation after the 2010/2011 Christchurch earthquakes revealed. We look at which roads held up best. Viewing road damage a er the Christchurch earthquake.
Public Works May Jun 2013
Public Works Professional Sept - Oct 2013