Site investigations types
Site Investigations are being carried out to gather further information about ground and environmental conditions to ensure that we have the best, most up-to-date information available as planning for the city's newest rail line continues.
To find out what works are currently taking place, see our Works in your area page.
If you have any questions about our site investigation activities please contact us.
Why are we undertaking arborist assessments?
Arborist assessments are being carried out on a number of trees along the project alignment. Arborist assessments will document the size and health of trees, their proximity to the project alignment and assess the potential impact of the project on nearby trees.
The information gathered from the tree assessments will inform project planning, including identifying and minimising potential impacts to trees from construction and operation of the new rail line.
How and where are these assessments being undertaken?
Assessments are being undertaken in public areas along the project alignment, between Kensington and South Yarra, by a team of up to four arborists. The studies will involve:
- Visual inspections to determine tree health, including evidence of insect infestation, soil pathogens and fungus.
- Measuring the height and circumference of trees.
- Assessing tree structure, including tree roots and canopy.
During these assessments you may notice specialists examining trees and the surrounding soil, taking photographs and making notes on paper or a tablet computer.
Why are we undertaking basement surveys?
We have identified a number of properties along the proposed project alignment that have basements. To understand how the project's underground tunnels and stations will integrate with below ground features such as basements, we need to undertake a visual inspection and 3D laser scanning to ensure we fully understand the underground landscape in which the project will be built.
The information gathered through these studies will help inform project designs and proposed construction methodologies.
What does the survey involve?
The investigations will involve a surveyor and structural engineer undertaking a visual inspection and 3D laser scanning of basements within buildings located near the proposed alignment.
The visual inspection will involve taking photos of the basement to help document the existing dimensions and condition of the basement.
The 3D laser scanning will involve a surveyor using a handheld device to scan the inside of the basement from various locations to produce a 3D image of the basement and its dimensions.
Both activities will be completed at the same time and will take up to one day to complete (subject to the size of the basement).
Cultural heritage surveys
Why are we undertaking cultural heritage investigations?
We are undertaking cultural heritage investigations to identify any Aboriginal cultural heritage artefacts present in the vicinity of the proposed project.
We have worked together with the Office of Aboriginal Affairs Victoria and Traditional Owner Groups to identify areas that require investigation.
The findings from these investigations will guide the development of a Cultural Heritage Management Plan, which will recommend measures for the management and protection of Aboriginal cultural heritage.
What will these investigations involve?
Work at each location will involve:
- Setting up temporary fencing around each site.
- Checking the site for underground services using non-destructive digging techniques
- Digging a pit and sifting through the soil to identify any items of Aboriginal cultural heritage
- Backfilling the pit and moving to the next site.
All sites will be restored their original or similar condition once all works are complete.
Just like the landscape above ground has features like hills, rivers and different types of soil, underground Melbourne has its own landscape. This landscape includes a variety of geological conditions such as hard rock, softer rocks and clays, silt deposited by rivers and groundwater.
Geotechnical investigations will help us to gain a greater understanding of local geological conditions and assist in planning how the Metro Tunnel will be built and will involve drilling into the ground to obtain rock and soil samples.
We are undertaking a range of investigations across the project corridor to better understand local ground conditions and the location of underground services ahead of the start of major construction.
Where are we drilling?
The geotechnical drilling program involves drilling approximately 200 boreholes across the project from Kensington to South Yarra.
At each location, there will be multiple sites and drilling will take place progressively. Advance notice of geotechnical investigations will be provided to residents and businesses before work begins.
The timing of these works may change depending on weather and ground conditions. We will notify surrounding residents and businesses if there are significant changes to the program.
What do geotechnical investigations involve?
Geotechnical investigations will be carried out between the hours of 7am to 6pm, Monday to Friday and 8am to 5pm, Saturdays. At each drilling location, the works will involve:
Stage one: Site establishment
Site compounds of varying sizes will be set up to enable the work to be carried out safely. These areas will be reinstated at the completion of each borehole.
Stage two: Service identification
Prior to the commencement of geotechnical drilling, we will undertake non-destructive digging which involves using a vacuum truck to dig carefully into the ground to confirm an area is free of services.
Stage three: Geotechnical drilling
100-millimetre diameter boreholes will be drilled up to a depth of 50 metres to retrieve a core sample which will provide information on ground conditions in the area. Drilling is expected to take around one week to complete at each borehole.
Stage four: Well development
Groundwater and other materials which may have entered the well during drilling works will be removed following geotechnical drilling. Well development will typically take half a day but may extend to a full day depending on the amount of groundwater encountered.
Stage five: Groundwater sampling
Groundwater will be pumped from the borehole at a steady, controlled rate and groundwater samples will be recovered. Sampling will typically take a few hours to half a day to complete. Inspections of the groundwater well will be carried out every 2-3 weeks for several months to sample groundwater and measure groundwater levels.
What can you expect?
Geotechnical drilling is expected to be low-impact, however, there may be some dust and noise generated during site establishment on the first day at each site, when rock breaking and digging is taking place.
Once drilling begins, this activity generates a small amount of noise, similar to that of an idle truck engine. All efforts will be made to minimise impacts on local residents and businesses.
During the works, there may be temporary changes to traffic and cycling lanes, pedestrian access and public parking spaces.
Please note that if our works require closures of traffic and cycling lanes, traffic management will be in place to direct traffic, cyclists and pedestrians safely around the work site when there are impacts to access. Changes to traffic conditions may also require speed restrictions to be put in place around our work sites.
Impact on parklands
For drilling works in parklands, management measures such as bog mats will be implemented to minimise impacts to grassed areas and surrounding trees.
After investigations are completed
All sites will be restored to their original or similar condition once all works are complete.
Geotechnical drilling in a particular location does not necessarily mean the Metro Tunnel will be built in that area.
Ground surface surveys
The ground surface survey is a low-impact activity designed to help us understand the way electrical currents may travel through certain ground conditions. The survey will involve laying a 50-100 metre line of metal probes at several locations listed below. The small metal probes will be inserted approximately 5cm into the soil at regular intervals, and will collect data by releasing a low electrical current into the soil. A meter box will be set-up to measure the resistance of the electrical current through the ground.
This survey needs to be undertaken in a number of parkland areas across the alignment as the probes cannot be inserted into asphalt. This method is commonly used in public spaces to test soil profile and density. The ground surface survey will not have any impact on public safety or the environment, and is expected to take up to one day to complete.
What does the survey involve?
The ground surface survey will involve:
- Checking the site for underground services using ground penetrating radar
- Sectioning off the work area using bollards and tape
- Setting up a 50-100 metre line of metal probes, and inserting these by hand to a depth of approximately 5cm
- Removing the probes on completion of the test
These works are expected to be low-impact and will not produce any noise or dust.
Why are we undertaking groundwater monitoring?
Groundwater monitoring inspections will be conducted at a select number of pre-existing boreholes and at some of our newly established boreholes to determine how construction activities could potentially influence groundwater sources in and around Melbourne.
The groundwater wells are located on both public and private land within 1.5 kilometres of the project alignment between Kensington and South Yarra.
What does groundwater monitoring involve?
Groundwater monitoring is undertaken by a specialist consultant who will perform a visual inspection by lifting the lid of the well and taking a photo. Once the lid is replaced, the consultant will leave the property.
This is a non-intrusive exercise that is expected to take no more than 30 minutes per well. Access to all private property will be pre-arranged with property owners prior to inspections being undertaken.
What is laser scanning?
3D laser scanning will be undertaken at various locations along the project alignment. Laser scanning technology allows the project to catalogue existing site conditions using photographs taken from a number of viewpoints to build a 3D model of the current environment.
Why are we undertaking laser scanning?
Laser scanning will help to determine potential impacts from construction and operation of the new rail line on the existing environment.
What does laser scanning involve?
3D laser scanning will involve a team of two people:
- Assessing the current urban environment in the vicinity of the proposed rail tunnel entrances in Kensington and South Yarra and in the vicinity of the proposed underground stations at North Melbourne, Parkville, State Library, Town Hall and Anzac.
- A scanner mounted on a tripod which will take a series of images over a 15 minute period in each location.
- Taking written notes to observe findings.
Level settlement monitoring will help us to understand horizontal and vertical ground movements along the proposed alignment during construction.
The data gathered will form a baseline, allowing us to identify if any changes to ground levels have occurred during construction. Level Settlement Monitoring is a standard activity undertaken in advance of any major construction project.
Undertaking this type of monitoring does not mean that we expect ground movement to occur as a result of the project, in fact, a range of mitigation measures will be built into construction planning such as grouting, groundwater monitoring and, if necessary, groundwater recharge, to manage any potential ground settlement impacts of the project.
Three types of Level Settlement Monitoring devices will be used to understand horizontal and vertical ground movements:
- Array Point: Similar to a household nail, these devices are drilled into the ground using a hand-held drill. They will be placed at 10-30 metre intervals along public footpaths and on the grounds of the University of Melbourne.
- Settlement Monitoring Points: These devices are between one and five metres in length and are approximately 10cm in diameter. They will be inserted into the ground using a truck-mounted drilling rig. A metal cap will be placed on top of the device to protect it. These devices may be installed in roadways, footpaths or parkland.
- Permanent Survey Bench Marks: These are similar to the settlement monitoring points but are between 10 and 20 metres in length. They will be installed into the ground using a drilling rig. A metal cap will be placed on top of the device to protect it. These devices must be installed in areas of solid rock to provide a reference point to measure ground movement in an area. Like the Settlement Monitoring Points, these devices will be installed in roadways, footpaths or parkland.
Noise and vibration
Why are we measuring noise and vibration?
The purpose of the studies is to understand existing levels of noise and vibration in the urban environment. This will help us to:
- Assess current and future noise and vibration levels in these areas.
- Inform project designs and strategies to minimise potential impacts from noise and vibration during construction and operation of the new rail line.
How are we measuring noise?
Noise studies will be undertaken using two different methods:
- Attended studies, where consultants are present during the shorter-term monitoring event (generally up to 30 minutes). These assessments will be undertaken in public areas.
- Unattended studies, for longer-term data capture where logging equipment will be left for up to one week to log noise levels in the surrounding environment. These assessments will be undertaken on private property.
How are we measuring vibration?
Loggers will be placed on surfaces, such as footpaths, to record vibration events enabling consultants to identify peak vibration levels and measure these against specific events, such as passing trams or traffic. These measurements will be recorded at a number of locations for approximately 30 minutes. All assessments will be undertaken in public areas with consultants accompanying the equipment at all times.
How are we measuring noise and vibration in the Yarra River?
Noise and vibration studies will be undertaken in the Yarra River to document current underwater noise and vibration levels, which will help assess the potential impact of construction activities on aquatic life within the river.
These studies involve acoustic consultants lowering aquatic loggers into the river for approximately 30 minutes to obtain this data.
What is geophysical testing?
This testing will help us understand how vibration travels through the ground so we can plan for and manage future construction impacts during the excavation of major shafts, tunnels and stations; as well as understand potential operational impacts from trains running through the tunnels and stations.
We will be undertaking two types of tests over two nights:
- For the first test, we place geophones (a device that records ground movement) down an existing borehole and generate energy by using a hammer striking a metal plate on the ground continuously over a number of hours.
- For the second test, we put compressed air down an existing borehole. Geophones are placed on the ground and record the vibration Peak Particle Velocity (PPV).
This testing needs to take place at night or in the early hours of the morning (between 8pm and 8am) when there are fewer competing sources of vibration such as trams or trains.
These works will take approximately six hours on each occasion. While we will keep the disruption to a minimum, there will be noise generated throughout the works. We apologise in advance for any inconvenience while we undertake these essential investigations.
Signs will be used to direct pedestrians safely around the work sites. Please obey any signage on site. The testing sites will be restored to their original or similar condition once all works are complete.
What is Continuous Sound Wave Testing?
This testing generates vibration at the ground surface. This vibration is measured using six geophones (a device that records ground movement) set out along the ground surface (for approximately five metres).
This testing needs to take place at night or in the early hours of the morning (between 7pm and 8am) when there are fewer competing sources of vibration such as trains and vehicles. The testing will take approximately four hours.
While we will keep the disruption to a minimum, there may be noise generated throughout the night. We apologise in advance for any inconvenience caused while we undertake these essential investigations.
We will be using mitigation measures such as noise blankets to decrease the amount of noise that we may generate.
The testing site will be restored to its original or similar condition once the works are complete.
Investigations are being undertaken to identify the location of underground services in areas along the project alignment. These investigations include two activities, preliminary service investigations and trenching activities.
Preliminary Service Investigations
Electronic detection and visual inspections
Preliminary service identification involves the use of electronic detection equipment to confirm the location of underground services in the area.
Electronic detection is a safe and reliable method for accurately determining the location of underground services. Crews will be walking along the streets with Electromagnetic Field equipment to locate pipes and cables beneath the surface, and determine the alignment and depth of those services. These investigations will also involve lifting the lids of service pits and performing visual inspections.
Trenching activities will help confirm the location of underground services.
This activity will involve the excavation of narrow trenches in roadways and footpaths in areas along the project alignment. These works are proposed to be undertaken out of business hours to help minimise impacts to traffic and pedestrians.
There will be some noise during saw-cutting for trenching activities however we will use noise barriers to minimise the level produced.
Managing traffic and parking impacts
To safely complete these activities, local traffic along these streets will be managed using a stop-go arrangement to maintain the flow of traffic. You may experience minor delays while our crews attempt to quickly and safely complete these activities.
Car parking will not be affected, and access to private properties and businesses will be maintained at all times.
Hours of work
Electronic detection and visual inspections will be carried out between the hours of 8pm - 5am, Monday to Friday, although every effort will be made to complete these activities ahead of schedule.
There may be some noise associated with these activities, however, every effort will be taken to minimise any potential impacts.
The timing of these works may change depending on weather, and we will notify surrounding residents and businesses if there are significant changes to the program.
What will these studies involve?
A team of assessors will undertake a range of visual inspections to document the existing conditions of areas along the project alignment. The assessors will take photographs to document the current condition of the urban environment.
These studies will be conducted on both public and private land but are largely non-intrusive. Where access is required to private property, we will contact the property owner and/or tenant directly to arrange the necessary approval to undertake these surveys.