Earthquakes and Pavement Resilience

In September 2010, the Canterbury region of New Zealand was shaken by a 7.1 (ML) magnitude earthquake which caused significant liquefaction and slope failures, followed by over 10,000 aftershocks and major earthquakes during the next 18 months. An investigation was carried out to assess the performance of various pavement structures used in Christchurch and surrounding districts, to identify what were the most resilient pavements for the reconstruction of roads in the region. The most common pavement type in Christchurch and surrounding districts consists of chip seals over unbound granular bases and subbases. Following site inspections and analysis of data and photographs, five main failure mechanisms caused by the seismic events were identified; these are explained in this paper. A pavement treatment selection procedure for post-earthquake repairs was developed and was implemented. Significant conclusions are: (1) The most resilient pavements in seismic events, considering factors such as level of service after the event(s), survivability of the pavement and economics of repair, are thin-surfaced unbound granular and foamed bitumen stabilized pavements; (2) Aggregate in unbound granular pavements could be contaminated with up to 30% liquefaction material without adversely affecting its performance; and (3) The liquefaction was often trapped in lenses under pavement layers and surfacings of lower permeability and created bulges, leaving the surfacing intact. The only means of repairing these bulges is to remove layers overlying the lenses of liquefaction material and replace with new construction.