ABSTRACT
The application of Unmanned Aerial Vehicles (UAVs) and photogrammetry for bulk earthwork calculations is a recent development for ground engineering in New Zealand. The approach developed on the Deans Head Land Remediation Project has proven to be an innovative solution increasing workflow efficiency to calculate and reduce uncertainty during bulk earthworks.
Following the 2010-2011 Christchurch Earthquake Sequence, Deans Head and Shag Rock Reserve, located near the suburb of Sumner, Christchurch, suffered significant land damage. Subsequently, Shag Rock Reserve was inaccessible to the public and Deans Head was assessed as being in the highest relative landslide hazard category with a potential risk to life and/or cause significant lifeline damage.
This paper presents the application of UAV and photogrammetry technology, outlining the ‘Fly-Model-Analyse’ workflow to generate accurate change models on the Deans Head Land Remediation Project. UAV and photogrammetry methods are compared with traditional methods for volumetric calculations, such as LiDAR, ground surveys and truck count estimates. The associated emerging technologies to enhance its application for ground engineering and some of these progressions and future uses are explored.
1 INTRODUCTION
1.1 Outline
The recent advancement of UAVs and photogrammetry applications has enabled the project team to develop a workflow process to reduce the uncertainty in bulk earthwork calculations. Traditional methods including truck count for volume estimates and ground surveys were taken into account during project establishment however considered time consuming and labour intensive and more importantly placed staff into high risk areas. An alternative method that is safer, quicker and allowed third party verification was required by key stakeholders to meet their regular reporting requirements.
A proficient workflow system was created using UAVs and photogrammetry to calculate key volumes that were required every fortnight on the project. Increasing project efficiency reduced personnel working in high risk and complex, steeply inclined slope with heavy earthworks machinery.
1.2 Background
Following the 2010-2011 Canterbury Earthquake Sequences, significant land, property and infrastructure damage was observed south of Christchurch at the foot hills of the Port Hills (GNS Science, 2013). Located near the suburb of Sumner, Deans Head and Shag Rock Reserve were badly affected by the severe ground shaking, resulting in collapse of the 80m high volcanic cliffs above Shag Rock Reserve and dense ground cracking across the steep Deans Head hillside area.
Following the Canterbury earthquakes, GNS Science (Massey et al., 2014) identified numerous mass movement areas in the Port Hills. Identified as a Class I mass movement area, the Deans Head area extends approximately 8,300m2 in size and contained an estimated 53,300m3 of soil (loess) material that could be mobilised as an earth/debris flow likely to have debris runouts which could cause damage to critical infrastructure, lead to loss or disruption of services and/or loss of life. Based on recorded surface movements and slope displacements across the site area, the landslide direction has been modelled in a northwest direction in relation to the site with trigger mechanisms rain related. Located on a steep sloping hillside, Deans Head has an average slope angle between 25° to 30°. Deans Head and Shag Rock Reserve site locations are presented in Figure 1 including the Deans Head indicative landslide direction.
