Lateral spreading and its impacts in urban areas in the 2010-2011 Christchurch earthquakes

In the 4 September 2010 (M-W = 7.1) and 22 February 2011 (M-W = 6.2) earthquakes, widespread liquefaction and lateral spreading occurred throughout Christchurch and the town of Kaiapoi. The severe soil liquefaction and lateral spreading in particular caused extensive and heavy damage to residential buildings, Christchurch business district (CBD) buildings, bridges and water supply and wastewater systems of Christchurch. After the earthquake, comprehensive field investigations and inspections were conducted to document the liquefaction-induced land damage and lateral spreading displacements and their impact on buildings and infrastructure. The results of ground surveying measurements of lateral spreads at approximately 120 locations along the Avon River, Kaiapoi River and streams in the affected area reveal permanent lateral ground displacements at the banks of upto 2-3 m that progressed inland as far as 200-250 m from the waterway, causing significant damage to structures located within the spreading zone. Different features and magnitudes of spreading were identified, which were often affected by a complex interplay of ground conditions, topography, meandering river geometry and local depositional environment. The spreading was characterised by very large and highly non-uniform ground deformation causing stretching of building foundations and the buildings themselves. Road bridges suffered a characteristic spreading-induced damage mechanism including back-rotation of the abutments associated with deck pinning and damage at the top of the abutment piles. The wastewater system of Christchurch was hit particularly hard by the liquefaction and lateral spreading, and approximately 60% of the damaged pipes of the potable water system were located in areas of severe liquefaction and lateral spreading.