Geotechnical Slope Hazard Design Team
Keywords: Lessons Learned, NCTIR, Natural Hazards, Disaster Response, Kaikōura
This paper captures the lessons learnt from the Geotechnical Slope Hazards Design Team over the approximate four-year duration of the NCTIR (North Canterbury Transport Infrastructure Recovery) project. The paper is an assimilation of a number of responses from the members of the design team throughout the project’s life. There are several lessons that were learned through the duration of the project that the authors hope will not only improve the processes and approaches during future disaster recovery but also design approaches for future non-disaster recovery projects.
The paper is sectioned into the Key Learnings from the project (the five critical lessons recommended for adoption in large scale disaster recovery), followed by the Main Learnings gained during each stage of the project.
The main learnings represent important experiences and recommendations gained during specific phases on the recovery and design effort. In each phase there are major and minor learnings, as judged by the authors somewhat subjectively, defined as below:
Major Learning – A significant positive or negative learning experience that is strongly recommended to be adopted for future projects. These learnings have significant impact on the programme, operation, and safety of the project.
Minor Learning – An important note that would have improved the workings within the project and may provide some benefit on future projects.
In response to a number of unique challenges faced on this project resulting from the timeframes, terrain and multiple geotechnical hazards, a number of innovative solutions were developed. These key innovations have been captured within this paper and as part of these lessons learned, in the hope that these can provide benefits to the wider industry for future projects.
1. The NCTIR Programme
During the November 2016 Kaiko¯ura Earthquake, the North Canterbury region experienced significant ground shaking and slope failures. The North Canterbury Transport Infrastructure Recovery (NCTIR) alliance, representing the NZ Transport Agency (NZTA) and KiwiRail on behalf of Government, were tasked to repair the road and rail networks between Picton and Christchurch.
The scope that was managed and delivered by NCTIR is briefly summarised below:
- Establish access to Kaikōura via SH1 south and Inland Road (Route 70) to reconnect the Kaikōura community and enable Kaikōura to reopen as a tourist destination.
- Strengthen and manage the roading infrastructure on the SH1 alternate route (via Lewis Pass) to cope with the extra traffic and to improve safety and journey time for customers,
- Re-connect the road and rail links between Kaikōura and Picton.
- Restoration of the Transport System along the coastal route between Cheviot and Clarence
- Design and construct safety, resilience and tourist amenity improvements on SH1 between Oaro and Clarence.
- Reinstate a safe, functioning Kaikōura Harbour.
- Provide environmental, planning, consenting, and stakeholder management for the above works.
Within the programme, the NCTIR project naturally evolved to have two distinct phases, which directly impacted the design processes and the way in which the team operated.
The Emergency Response phase included the immediate remediation and slip clearance work to re-open SH1 and reconnect the Kaikōura community. During this time two detours were in place. The Inland Route (Route 70) detouring the southern section of SH 1 to access Kaikōura, and the “Alternative Route” to provide access between Christchurch and Picton, which detoured on SH7, SH65 and SH6 (from Waipara to Nelson via Lewis Pass and Murchison).
The Recovery phase, which focussed on reinstating the network to full operation and improving the coastal journey. This phase also included works to improve the resilience of the network to future events.
2. Key Learnings for Future Disaster Recovery Projects
In essence, the key learnings are six critical lessons that are considered ‘essentials’ to be adopted on future large-scale infrastructure disaster recovery projects. Many of these consistently came across in the majority of the responses received.
Key Learning 1 – Recovery Strategy
Develop a clear recovery strategy that includes consideration for the immediate goal of re-opening critical lifelines as well as the recovery phase of building resilience. Having a pre-formed plan and strategy for each section of network to improve resilience following disasters may facilitate this approach.
Key Learning 2 – Prepare for Change
Be prepared for the design approach to change as the project evolves. The initial approach during the response phase was driven by timeframe and life safety risk, which resulted in standardised designs, with construction and design occurring concurrently. Later in the project, during the recovery phase, a Target Out-turn Cost (TOC) approach directed the project towards a more traditional design and construct approach along with a focus on improving the resilience of the network.
Key Learning 3 – Team Structure
Building a high performing team that works well together is key to the success of the project, as demonstrated on NCTIR. The team would have benefited from a Technical Specialist from the Client(s) being embedded within the project to work alongside the design teams. Efficiencies in workflows could be improved by creating integrated teams of mapping, modelling and design responsible for specific sections of the transport corridor. In addition, implementing well-constructed spatial data collection system, such as Fulcrum or ArcCollector, from the start of the project would improve the consistency and transfer of information.
Having a mixed team of Engineering Geologists and Geotechnical Engineers is essential. The team must be trusted to work within their respective areas of competency. Professional registered Engineering Geologists (PEngGeol) must have equal responsibility and authority for signing off works relating to their field of expertise, without needing to defer to a Chartered Professional Engineer (CPEng).
Key Learning 4 – Earthquake Damaged Slopes are Different
Effectively communicate and ensure an understanding by non-technical Asset Owner representatives that there will be a number of sites very prone to failure that have not directly failed during the earthquake. These failure-prone slopes should be considered, and the recovery should not solely focus on only the slopes that failed, especially if there is a desire for resilience.
Key Learning 5 – Slope Works
The risk to workers on slopes (roped access) and at the base of slopes needs to be critically reviewed during any recovery project, especially following seismic events where aftershock sequences can be complex and extended. This review must consider other solutions to placing people on the slopes, especially for scaling. The team did not believe this risk to slope workers was fully appreciated, and that we were fortunate the Kaikōura earthquake did follow the same aftershock sequence seen in the Canterbury Earthquake Sequence.
Key Learning 6 – Network Resilience
Network resilience should be considered early in the project, even during emergency response. In this sense, ‘Resilience’ focuses on the long-term Robustness of the network against the increase in slope failure rate expected following the earthquake. An early focus on network robustness can alter the design solutions adopted and will allow for consideration of both life safety risk and long-term residual risk.
3. Main Design Lessons Learnt
The main learnings (major and minor as noted in the Introduction) represent important experiences and recommendations gained during specific phases on the recovery and design effort.
During the Emergency Response phase, the initial target for road opening was May 2017, six months after the Kaikōura Earthquake. This resulted in a focus on clearing material, assessing the risk and installing as many remedial systems as possible. The design philosophy took a corridor-wide approach, standardising structures and therefore limiting the need for site specific designs. This approach enabled a larger number of proprietary systems to be ordered early, which was necessary due to significant lead in times. However, once the May target was realised to be unrealistic, the design process refocused, still maintaining a prioritisation of speed, but now ensuring the available pre-ordered systems were optimised and tailored to the specific site.
Photo 1 – Slip P7, significant amounts of debris resulting in extensive damage to the road and rail corridor.
Following road re-opening in December 2017, the Recovery phase began, which focussed on reinstating the network to full operation and improving the coastal journey. This was completed using a Target Outrun Costs (TOC) approach, which led to a more traditional design-and-construct process. The designs were tailored to each site and optimised with a focus on the total project cost. In addition, further effort was focused on improving the long-term resilience of the rail network which resulted in several ‘Reliability’ projects for rail. The Reliability projects looked at more frequent return-period events and maintaining an improved level of surface.
3.1 Initial Brief and Design Philosophy
In the emergency response phase of the project, the NCTIR design team was directed to re-open the road and rail as fast as possible to an agreed acceptable life-safety risk and level of service. A number of design philosophies, including slope risk management, rockfall modelling and rock mass classification, were established to align the team and asset owners in this approach.
- Determine a clear strategy and directive around opening the lifelines in a safe manner as quick as possible, balanced with operational resilience to frequent events being incorporated.
- It is beneficial having key Design Philosophy Reports. For the NCTIR project the critical report covered rockfall, rockfall modelling, and stated how the design boulders and percentiles relate to actual risk reduction. The critical design hazards that need to be considered in future recovery programs may be different.
- Consideration is needed for areas that have may have not failed in the main event but have been damaged and are likely to fail in the near future, possibly within the timeframe of the design working life of a protection structure.
- A complex and possibly large aftershock sequence should be expected following any significant seismic event. Controls need to be very carefully considered if workers are placed in high-risk locations.
3.2 Field Assessment
The field assessment phase of the project began immediately following the Kaikōura Earthquake and continued throughout the project; however, the majority of this work was undertaken in the first 12 months. The main aspects of the field assessments undertaken were landslide mapping, the development of geotechnical characterisation reports for each failure site as well as the assessment of the life-safety risk to rail and road users.
- Prepare for an immediate use of GIS based mapping system (such as Fulcrum or ArcCollector) and define specific “locked” values. Spatially collected data is invaluable for design, site management, transfer of knowledge, quality and handover.
- Collect area-wide LiDAR as early as possible following an event, as well as regularly thereafter (approximately six-month intervals) to assist with large scale monitoring.
- Determine a consistent approach and/or guideline for the inspection of sites and landslides from the outset. This should be captured on GIS.
- Ensure the information collected in mapping and characterisation reports relates directly to the risk rating events captured in the risk assessment. For NCTIR the risk assessment frameworks used were
– The New South Wales (NSW) Roads and Maritime Services (RMS) Slope Risk Assessment Version 4, for Road. The NSW RMS calculates an Assessed Risk Level (ARL) with an upper level of acceptable risk of ARL3 required by NZTA
– The KiwiRail Slope Hazard Rating (KSHR) was used as a proxy for risk for the rail network, with an upper limit of tolerability of 250 required by KiwiRail.
- It is useful to develop a localised specific Rock Mass Classification early to aid in standardised description and communication of slope materials being studied. [e.g. Macfarlane & Justice (2017)]
- It is beneficial to have a geotechnical mapping team independent of the emergency clearance and construction support team.
- Site-specific characterisation reports should be concise and templated to capture key information relating to the observed and reasonably expected hazards affecting the life risk and that would be used as the basis for design.
- Develop a non-sequential naming convention of sites — using chainages or unique locations names, to allow additional sites to arise, and be named, between sites.
- The widespread use of UAVs (drones) would have helped collect large amounts of site photography at a much more efficient cost compared to helicopters. Simple training and restricted airspace mitigates most of the risk associated with drone usage.
3.2.2 Risk Assessment
Road and rail used separate risk assessment tools to identify the sites requiring remedial works, as well as assessing the suitability of proposed solutions. The road network used the New South Wales (NSW) Roads and Maritime Services (RMS) Assessed Risk Level (ARL) approach. The rail corridor used the established KiwiRail Slope Hazard Rating System (KHR). Sites affecting the road were considered needing to meet a residual risk level of ARL 3 or better. Sites affecting rail was required to have a score no greater than 250 at the completion of mitigation works.
- The risk rating tools (ARL / KHR systems) should be considered as a tool for prioritisation of detailed investigation and design, rather than a clear-cut quantitative risk assessment. These tools should be used within their limits. “Make Safe” criteria should be based around a different metric.
- Understand and communicate clearly that the outputs from risk rating tools (ARL and KHR) are limited and require expert judgement within the overall risk assessment. Especially for sites experiencing multiple failures in a short time period.
- If the ARL assessment is restricted to be used only by accredited assessors, the assessment then must be completed in accordance with the guidance, to ensure the capture of true risk. Limiting the assessment to focus on specific return period events, for example linked to the Bridge Manual SLS and ULS return periods, is considered inappropriate and should not be applied.
- Infrastructure asset owners (road and rail) are strongly recommended to implement a national collection of data from rockfall or landslide events to aid in risk assessments in the future – create a baseline to enable the post-seismic effects to be measured.
Photo 2 – Slip P6, the road at Ohau Point was completely buried by debris.
The analysis of the field assessment data was mainly completed in the form of rockfall modelling, although later in the project debris flow modelling was incorporated. The analysis and modelling outputs fed directly into the detailed design phase of the project.
3.3.1 Rockfall Modelling
- Rockfall modelling and the reporting needs to reflect the accuracy of incoming data, including both slopes and boulder sizes. The modelling approach needs to be as simple, repeatable and as practical as possible. The outputs from modelling are for analysis alongside other factors to assist in design.
- Rockfall modellers and designers should work in close collaboration within integrated modelling/design teams within a set zone or area to ensure close connections, accurate information, and timely delivery of outputs.
- Capturing rockfall data whether intentional (scaling triggered) or unintentional (event triggered) on video for determining modelling parameters is valuable. Equip site teams with high-quality cameras and lenses to capture this data.
3.3.2 Debris Flow Initiation and Modelling
- Following a significant landslide event, be prepared for debris flows following subsequent rainfall events. Expect debris flows to be initiated in significantly smaller rainfall events compared to what might have been experienced before the earthquake.
- Apply modelling tools that consider hydrographs with bulking factors and utilise inputs from stormwater modelling to provide shape of catchment and flow rates.
- Where possible collaborate with national agencies (such as NIWA and GNS) to expand any landslide dam breach modelling to include high-risk debris catchment areas.
Photo 3 – A significant debris flow at Jacobs Ladder following ex-Cyclone Gita.
The design work completed by the NCTIR Geotechnical Slopes Hazard team focused on the remediation of landslides and rockfall protection systems to reduce the life-safety risk to road and rail users. Throughout the lifetime of the project the approach evolved from the rapid design/construction in the emergency phase through to ‘traditional delivery’ during the recovery phase and resilience work.
3.4.1 Design of Works
- Identify a suitable design guidance for rockfall protection structures. In most cases, the NZTA Bridge Manual is not appropriate for rockfall protection, and further guidance needs to be developed around seismic demands on anchorages. The applicability of design working life on rockfall protection structures and their anchorages also need to be reviewed considering the frequency of impact on the structures during their design working life.
- The Bridge Manual anchor corrosion protection clauses need review for rockfall protection structures. Consideration is needed of the appropriateness of the required protection coatings and the significant associated costs. Several departures from Bridge Manual requirements were granted by NZTA for this project in this regard.
- Adopt an internationally recognised certification (such as ETAG 027) to ensure suitability of protection fences and mesh then design anchors accordingly.
- Undertake total life cycle cost assessments of fences and mesh (particularly with consideration to their high maintenance costs) when considering against realignments and other major works and options.
- Embed a technical Asset Owner representative within the design team with appropriate Delegation of Authority on technical issues. If this option is not practical, ensure Asset Owner technical representatives are included in design philosophy discussions, brought onto each project early and included in key decisions to expedite design outputs.
- Carefully consider the impact of the construction (and removal) of temporary works and the impact on permanent works. Notably, cutting benches into lower slopes to ease the install of permanent fences can lead to long-term slope instability issues of the bench.
- Carefully consider the lateral extents of rockfall protection works. Often the rockfall zone terminated against a steep rock bluff, and most off-the-shelf solutions did not cater for this.
- It is beneficial to have a pragmatic in-house geotechnical peer reviewer, that understands the driving issues, applies practical solutions and provides clear reasonable input. This role has the ability to add a lot of value to the team, as proven on the NCTIR project.
- Realignments, bunds, and walls have lower maintenance costs than fences, and should be considered as the preferred option. Use fences and mesh sparingly and only when geometrically constrained.
3.4.2 Safety in Design (SiD)
- Include site specific SiD Risk Registers in the drawing set for each project.
- SiD Risk Registers must be unique for each site, whereas Project Risk Registers may be suitable to be generic across a series of similar projects.
- From a SiD perspective, upslope barriers and fences will require significantly more safety considerations during their construction and will have increased maintenance issues compared to drapes, attenuators and other self-clearing structures that require non-specialist contractors to clear debris with standard equipment at road level.
- A strong SiD culture leads to innovations – see Section 4 below.
- Ensuring consistency of information between characterisation reports, risk assessments, rockfall modelling and final design reports is important. This could be achieved through a zonal team structure.
- Overly detailed and lengthy reports are excessive and unnecessary for authors, reviewers, and asset owner representatives. Lengthy reporting for each site can result in excessive review work from the client side resulting in delays on the project side. A recommended approach is to capture project and site wide information in an overarching philosophy report with short site-specific design features / calculation reports.
- An Operations and Maintenance Manual covering a particular asset stream, such as rockfall protection structures, is beneficial and combines critical operational information into a single document.
- Ensure the documents storage/release platform is user-friendly, especially on site. A good search function and automated association of RFIs is needed to effectively track design changes and instructions to site.
- It is beneficial to use a risk-based assessment (ARL) for road re-opening purposes, compared to the use of producer statements – PS4 for works completed. The temporary opening of the road relied upon a PS4 signed to CM1-CM2 level for each region (Kaikōura North and Kaikōura South). This was felt to be inappropriate given the traffic volumes and the number of people at risk.
- It is beneficial to set out a streamlined and achievable review process between designers and asset owner technical representatives.
- Standardise common details from the start (e.g. anchor assemblies, FlexHead details, etc. for rockfall protection structures).
- Include SiD Register and Specifications (including testing requirements and anchor schedules) within the drawing set for each project.
- Ensure drawings are as detailed and site specific as possible to communicate clearly the design intent. This is benefited by including tolerances of geometries, anchor depth and spacing, and finished structure heights etc.
- Standard drawing scales should represent the size most printed for use on site (i.e. A3).
- It is beneficial to implement, track and record drawing read-throughs with designers, site engineers and CPS (Construction Phase Services) team to communicate design intent and key details.
- It is beneficial to use digital design models for complex structures. In these cases, the drawings should be extracted directly from the digital model to avoid multiple sources of information.
3.5 Construction Phase
Due to the geographical separation between site and the design office, the team included a number of design representatives that were site based. The CPS team consisted of a number of geotechnical professionals that provided design presence on site. The CPS evolved from the site based “Geotech Team” that provided the technical input for the remedial works and slip clearance during the emergency phase.
- It is beneficial to have a collaborative approach between construction teams and the design team (their site representatives) through the tendering, scoping and review process to ensure details on the drawings are not underappreciated.
- It is essential to include the Design/CPS team during the procurement of materials to prevent the wrong items being ordered, especially considering some items can have extended lead-in times, and the wrong materials can cause significant delays to the project.
- Ensuring collaborative and open communication between designers and the site-based CPS team is critical. In the initial phases, having a site-based principal-level designer imbedded in the CPS team with a level of delegated authority would be beneficial when designs and drawings are ‘work in progress’.
- Site observations (including rockfall events), design queries and requests for information between design, CPS and construction teams should captured in a formal communication – this benefits transfer of information and records discussions.
- Ensure hazard assessments and risk ratings are well communicated with site teams, especially those working on slope, as well as STMS teams selecting locations for TTM and queuing vehicles
- Wind can cause loosening of shackles in a very short period of time, ensure all shackles are “moused” and secured.
3.6 Quality and Handover
Although not directly responsible for the quality and handover process on the project, the Design and CPS teams were involved with aspects of the process regarding the rockfall protection systems designed and constructed over the life of the project.
- It is beneficial to use tested and certified products (such as proprietary rockfall protection systems),
as this simplified the design and construction of complex dynamic structures and provided assurance of their capability.
- During the emergency response and rapid recovery stage, QA needs to be consistently captured to reduce the need for any re-work or poor work being accepted out of necessity. As-built information must be accurately captured throughout construction and finalised immediately after being built.
- To minimise the time lag between completion and handover, regular (weekly or bi-weekly) meetings solely focused on QA tracking is essential.
- Provide the CPS Team with suitable time and resources to enable them to capture as well as review of QA documentation at the time of construction to facilitate the handover process.
- Duplication of producer statements creates unnecessary paperwork. If standard producer statements are required, then internal ones should not be created. The value of an internal design certificate should only be considered for systems that do not require a standard producer statement.
- Multidisciplinary checks, ‘Squad Checks’, are useful when applied appropriately, to efficiently gather large amounts of diverse feedback from relevant parties.
The major learning from the NCTIR Design Team’s perspective of maintenance is that during the emergency recovery and ‘road opening’ phase the maintenance requirements of structures were not heavily considered. Speed of install, and suitability of the solution for the hazard took priority.
The proprietary structures from Europe appear to be designed for different financial models. The geotechnical environment in New Zealand, particularly earthquake damaged slopes within Torlesse Greywacke rocks, has a much larger amount of fretting and minor rockfall that require much more frequent clearance compared to what appears to be the case in Europe. This presents a significant challenge and may result in higher long-term maintenance costs compared to other solutions.
Photo 4 – Accumulation of debris will require ongoing clearance and maintenance of the structures.
NCTIR developed a strong culture of innovation throughout the life of the project. This directly resulted in a number of novel solutions, modifications to proprietary and approaches to installation. The sections below outline the main innovations relating to the rockfall protection systems and were funded and supported by NZTA and KiwiRail during the NCTIR project.
4.1 Developed Solutions
4.2 Modified Structures
- Hybrid Attenuator Barriers – Increasing the length of the attenuator tail to reach close to road or bench level to improve ease of clearance.
- Removal of ‘apron’ on Shallow Landslide Barriers – If appropriate, removal of the uphill apron greatly improves maintenance behind the structure without impacting overall performance.
- Winglet Detail on Fences – At the lateral extents of rockfall fences and attenuators continue the mesh along the lateral ropes to create ‘wings’ to increase the catch area of the structure.
- Transmission Rope – An additional rope installed horizontally across the middle of a rockfall fence can significantly reduce the overall deflection when working in a narrow area.
- Additional Cable for Clearance – A tether can be attached to the centre of each span of a dynamic fence/barrier to facilitate in lifting the bottom cable to clear material from the structure.
- Turnbuckle on Bottom Rope – Install a turnbuckle on the bottom rope of an active mesh and/or drape system to facilitate easier release of material during clearance.
- Draped Debris Flow Barrier – Modify a debris flow barrier to have an extended drape covering a steep channel to provide storage for debris as well as better access for clearance of debris.
- Grade Marker for Bunds – Use a grade marker to mark the backslope of the bund, such that during clearance the profile of the bund can be visually identified to prevent damage to the structure.
- Concrete Roadside Barrier as Rockfall Protection – Using TL4 and TL5 concrete roadside barriers as part of the overall system to manage debris entering the transport corridor. May require modifications depending on energies.
- Seawall Block Bund – Using seawall blocks to construct bunds / bund facing, proved to be more time efficient than gabion baskets.
- Reinforced Erosion Matting as Temporary Drape – MacMat-R and similar products proved to be good temporary drape solutions across unstable slopes. It is relatively quick to install, can attenuate larger material and the fine poly matrix reduces the amount of nuisance debris released.
- Epoxy Coated Galvanised Bars – The use of epoxy-coated galvanised bars to provide a Class 2+ level of protection. This approach was considered by the design team and the KiwiRail/NZTA SMEs to be a practical, cost effective solution, and appropriate for the situation and systems used. A Departure from NZTA was required for their use on NCTIR.
- Early Contractor and Manufacturer Involvement – This is critical for any project to understand the limitations of construction during the design phase.
- GIS Based Data Collection – Fulcrum was used to collect and standardise field capture, including construction observations, slope movement reports and quality information. This system is beneficial if implemented as early as possible on a project.
- TARP (Trigger Action Response Plan) – a risk management tool that considers a number of factors ranging from weather forecasts to real-time monitoring. Can be developed further in place of structures to manage risk.
- Earth Fill Bunds – Assessing and using appropriate landslide debris as fill for earth bunds. Cost and time efficient.
- Rock Milling – Can be used to effectively scale rock faces below around 8m and can remove larger features on the rockface compare to conventional scaling.
- Digital Terrain Models – Using UAVs or helicopters to collect aerial imagery to build photogrammetric DTMs for use in analysis of the slope and boulders, identification of hazards, and in design.
- Digital Design Approach – Using the DTMs as a base to design structures in 3D using digital modelling software, this is more suitable for complex structures on challenging terrain.
- Realignments – Realign the transport corridor away from hazards where possible, is a very effective solution with minimal maintenance.
We would like to acknowledge the hard work and dedication of the NCTIR Geotechnical Slope Hazards Design Team; Cecile Coll, Cedric Lambert, Charlie Watts, Charlotte Steele, Clive Anderson, Dan Ashfield, Don Macfarlane, Doug Mason, Greg Saul, James Byron, James Grindley, James Stringer, Jayne Hodgkinson, Jen Kelly, Jesse Dykstra, Jono Claridge, Kelly Walker, Leeza Beecroft, Mark Easton, Mark McCallion, Matt Engel, Neil Charters, Paul Aynsley, Paul Clarkson, Paul Horrey, Richard Justice, Romy Ridl, Rori Green, Sarah Jones, Scott Barnard, Tiarnan Colgan, Tim Farrant, Tom Revell, Torben Fisher, Willy Marshall and others. The lessons captured could not have been completed without the numerous responses received back from the team.
We would also like to acknowledge the effort and commitment from Asset Owner technical representatives Stuart Finlan and Daniel Rodriguez and for their support of the lessons learned.
- Justice, R (2012). Development of a Slope Risk Rating System for New Zealand Rail. 11th Geomech Conf, Melbourne, July 2012
- Macfarlane, D., Justice, R. (2017) Rock mass classification for NCTIR Slopes. NZ Geomechanics News Issue 93-06/2017.
- NCTIR Document. Design Philosophy Report – Slope Risk Management, May 2019, Document Number: 100001-CD-GT-DP-0001
- New South Wales Roads and Maritime Services (NSW RMS); Guide to Slope Risk Analysis, Version 4 2014.