Figure 1. (Click for larger image [191KB])
RAPID: Field Investigation of Shallow Ground Improvement Methods for Inhibiting Liquefaction Triggering; Christchurch, New Zealand
Principal Investigator: Kenneth H. Stokoe, II, University of Texas at Austin
In 2010-2011, the city of Christchurch, New Zealand was devastated by a series of powerful earthquakes, including six significant events. The February 2011 Christchurch Earthquake (movement magnitude, Mw, 6.2) generated the largest ground motions in the city, with horizontal peak ground accelerations between 0.37 and 0.52 g. The 2010-2011 earthquakes caused repeated liquefaction throughout the suburbs of Christchurch. Some key observations and impacts are that: (1) liquefaction was particularly extensive and damaging along the meandering loops of the Avon River, now designated as part of the "Red Zone" (zone where structures will not be rebuilt), (2) more than 6,000 residential properties are being abandoned in the "Red Zone" because the damage is beyond economic repair, (3) an estimated additional 15,000 properties were affected by liquefaction, and (4) the total economic loss is estimated to be from 25 to 30 billion NZ dollars (or 15 to 18% of New Zealand's GDP). One critical problem facing Christchurch and the Canterbury region is rebuilding on land that remains at risk of liquefaction in future earthquakes. This problem arises after nearly all earthquakes and little information exists on ground improvement methods that can be used to increase the resilience of residential structures and low-rise buildings in future earthquakes.
Facing this critical, time-sensitive problem, the New Zealand authorities are contributing approximately $1M (NZ) to a project involving full-scale field test trials of shallow ground improvement methods. The goal is to determine if and which ground improvement methods achieve the objectives of inhibiting liquefaction triggering in the improved ground and are cost-effective measures. This new knowledge, which is applicable in the U.S. and worldwide, is rapidly needed as part of formulating the path forward in rebuilding the infrastructure in Christchurch and the Canterbury region. The New Zealand funds support all technical and logistical aspects of the project except the liquefaction testing. The liquefaction testing will be conducted using the large mobile shaker, called T-Rex
, that is operated by NEES@UTexas. T-Rex will be used to simulate a wide range of controlled earthquake shaking levels. This unique opportunity exists because T-Rex is already in Christchurch as a result of an earlier NEESR project involving deep seismic profiling.
Field tests were conducted between 6/15/2013 and 7/16/2013. Four different ground improvement methods were tested at two test sites. Figure 1 shows a photograph taken at one of the test sites. Figures 2 through 5 show the four different ground improvement methods.
Figure 2: Rapid Impact Compaction (RIC)
Figure 3: Rammed Aggregate Piers (RAP)
Figure 4: Low-Mobility Grouting (Compaction Grouting)
Figure 5: High-Mobility Grouting (Permeation Grouting)