Innovative Resin Injection Ground Improvement to Build Up Seismic Resilience of Existing Water Structures

Abstract

The existing Wellington Water’s Waterloo Water Treatment Plant (WTP) in Wellington, New Zealand is an important post-earthquake facility for the Wellington region. The WTP is founded on soils prone to liquefaction and cyclic softening in a large earthquake. Options for seismic strengthening of the WTP are currently being considered. Methodology for improving liquefiable soils beneath the WTP had to ensure that the plant is kept operational during the construction of ground improvement. Extensive field and laboratory testing of the site soils, including cyclic triaxial tests has been carried out. Innovative Resin Injection (expanding polyurethane resin) is considered to be the most efficient ground improvement option for the WTP. WSP geotechnical team, together with Mainmark contractors and Wellington Water, have designed and carried out a complex full-scale Resin Injection trial next to and beneath the WTP structures to refine the resin injection methodology and check the level of soil improvement that can be achieved. The trial required detailed heave monitoring of the plant’s floor and walls in addition to recording pipelines deformation in order to avoid causing damage to the plant structures and equipment. The trial indicated that Resin Injection resulted in a significant reduction in the treated soils’ liquefaction potential, as well as reduction in the predicted WTP structures’ seismic settlement and avoidance of seismic bearing capacity failures.