Choice 1: Dora Avanidou & Gavin Alexander

Dora Avanidou
Dora is a Senior Hydrogeologist at Beca Ltd. She is a professional engineer with a wide experience in water resources management, and environmental risk assessments. Dora holds a Master degree in Civil and Environmental Engineering from AUTH, Greece, a Master’s and a Doctoral degree in hydrogeology from USC, USA. She is currently member of the steering committee of IAH – NZ Chapter.

Abstract

The Mackays to Peka Peka Expressway is part of the Wellington Northern Corridor, identified as a Road of National Significance for New Zealand. The Expressway runs in close proximity to several wetlands of significant ecological and cultural value with unique fauna and flora, and to transport infrastructure and residential buildings built over peat deposits. Approximately 50% of the Expressway earthwork footprint is underlain by peat deposits that are typically 0.5m to 8.0m thick and are characterised as very soft, highly organic and compressible. Groundwater in the peat deposits is shallow and is directly connected to nearby wetlands. Expressway construction required either removal of the peat beneath its footprint or preloading and surcharging of it, to manage long term settlement. Both approaches involve significant potential alteration to the near surface groundwater system.

A comprehensive groundwater monitoring and settlement monitoring programme was established prior to construction commencing, with some 110 piezometers to record natural variations in groundwater levels and 100 settlement monitoring points.   In order to differentiate construction effects from normal seasonal variations, a statistical approach was developed for setting both high and low trigger levels for the 22 telemetered piezometers located in and around five sensitive wetlands. Recorded groundwater levels and settlement have generally remained within the consented levels. Some exceedances were recorded however a pragmatic approach to monitoring and management of these exceedances allowed works to continue with minimal disruption and no adverse environmental effects.

Read the full paper here.

Choice 2: Gislaine Pardo Tobar and Rolando Orense

Gislaine Pardo Tobar
Gislaine is a PhD candidate at the University of Auckland, in the Department of Civil and Environmental Engineering. Currently, the main focus of her research is to assess environmentally friendly materials as an alternative to mitigate soil liquefaction, trying to combine multidisciplinary cooperation through chemical-environmental and geotechnical areas.

Abstract

Currently, there is an increasing interest in providing more sustainable solutions for mitigating liquefaction and interdisciplinary work has started to introduce the use of nano-materials for this purpose. These materials have some advantages when compared with traditional techniques. For instance, they could be injected at low pressures or delivered into the natural ground water flow to treat a target area through passive remediation, which leads to less carbon emission production compared with normal grouting. In addition, after they gel, the nano-materials can provide increased shear strength and cohesion. This study focuses on the application of laponite, a synthetic nano-clay with the same structure as natural clays. Laponite suspensions have thinning behaviour characteristic in which its viscosity decreases with increase in shearing rate while keeping its gel properties. Moreover, after the shearing load is removed, the suspension recovers its viscosity in a self-healing process. In this study, the shear resistance of laponite suspension is studied by rheological measurements and the effect of the addition of 1% laponite (by weight) on the liquefaction resistance of the host sand is evaluated through cyclic simple shear tests. Results indicate that the number of cycles required to reach liquefaction is increased considerably for low shear stress conditions. In addition, by re-testing samples that have undergone liquefaction, the ability of the mixture to “heal” after liquefaction is confirmed. The results reaffirm the potential of laponite as an environmentally-friendly material for ground remediation purposes.

Read the full paper here.