Effectiveness of inhibiting liquefaction triggering by shallow ground improvement methods: field shaking trials with T-Rex at one area in Christchurch, New Zealand

摘要

Christchurch and the Canterbury region in New Zealand were devastated in 2010-2011 by a series of powerful earthquakes. The Christchurch area experienced widespread liquefaction that caused extensive damage. One critical problem facing the rebuilding effort is that the land remains at risk of liquefying in future earthquakes. Therefore, effective engineering solutions had to be developed to increase the resilience of homes and low-rise structures. To this end, a comprehensive series of full-scale field trials of multiple shallow ground improvement methods was performed. The field trials presented in this paper were conducted at one area in a severely damaged suburb of Christchurch and involved five test panels of different ground improvements. Each test panel and two additional test panels of unimproved natural soil were instrumented with embedded arrays of sensors and were characterized by crosshole seismic testing before shaking. A large mobile shaker, called T-Rex, was used to perform a staged-loading sequence of increasing sinusoidal horizontal loads at the surface of each test panel. The results of the staged-loading tests were successfully used to identify ground improvement methods that improved the ground performance versus those methods that contributed an insignificant improvement or even degraded the ground performance. The results of the pre-shaking crosshole tests were successfully used for two purposes. First, portions of the soils below the water table that were unsaturated were identified using compression wave velocities. Second, shear wave velocities were used: (1) to identify changes in the natural soil skeleton between improvements, and (2) to evaluate the effective shear stiffness of the combined improvement and surrounding natural soil. Further, the crosshole measurements led to development of a field verification method for use in evaluating changes created by shallow ground improvements.