With a wealth of experience in providing technical advice on corridor protection to asset owners, operators and developers, WSP’s experts have deep insights into managing risk without stifling the expansion of cities.
Here, Antoni Kuras and Jiping Pan explain six key underlying principles that will help those involved in approval processes.
1. Building near corridors needs extra approvals
Building development near protected transport corridors, if left unchecked, could impact the structural integrity of existing underground rail infrastructure (such as tunnels, caverns and subsurface structures) or restrict the construction of future underground infrastructure.
For instance, poorly considered foundation designs or earthworks could cause subsidence, alter loading profiles on tunnels and other engineered features, and, in the worst-case scenario, cause structural failure or even collapse.
Securing planning consent is therefore vital to ensure the safe operation of future and existing underground infrastructure. Whilst developers may see this process as a burden, it is a necessary means of building control for cities to maintain and improve their liveability and be Future ReadyTM.
Not all developers and consultants are familiar with negotiating the approvals process and completing the associated engineering assessments needed to support consent. To provide appropriate and tailored advice, consultants need a strong technical grasp of the fundamental engineering principles. The decisions made by the approval authority based on this advice should also be fair and not overly penalise the developer by imposing impractical or unrealistic technical conditions on the consent.
2. How close are you to a ‘no go zone’?
Within any city, there may be multiple transport infrastructure owners and operators with underground assets, and each is responsible for protecting their respective corridor. Invariably, each entity imposes their own set of protection guidelines or mandated requirements.
For cities to be Future Ready, city planners need to think about establishing these protected transport corridors sooner rather than later as part of their urban development strategies. Otherwise, as populations grow and cities develop, opportunities to build new transport routes may be lost or restricted at the very time that new public transport infrastructure or congestion-busting road or rail tunnels are most needed to maintain or improve liveability.
It’s vital that strong efforts are made to protect transport corridors early in the project planning process.
The most important step for any developer is to appreciate the physical position of their development in relation to the corridor. This can be challenging where the underground infrastructure is ageing, particularly if available survey information and as-built records are limited. Only once this physical relationship is understood and the guidelines or requirements appreciated, can a developer then correctly reference the relevant guidelines or requirements.
It is particularly important to understand the horizontal and vertical extent and profile of the protection areas or reserves that surround the infrastructure to determine if consent is indeed needed (e.g. is the development extending into a ‘no go zone’?), when consent is needed (e.g. do you need permission for a borehole during geological investigations?), and the type and nature of the constraints that could potentially be imposed on the development proposal. Significant inputs to this discussion are the size and shape of substratum that has been acquired by the asset owner. The zone usually represents an area below ground level into which physical elements of the new development must not intrude.
3. Never underestimate the ground conditions
Regardless of whether the underground infrastructure has been constructed yet or not, it is important to gain as detailed an understanding of the expected ground conditions as soon as possible, as this will be the basis for all the other analyses in relation to the proposed development.
Key geotechnical inputs need to be quantified to enable a reasonable, safe, cost-effective and prudent design. These inputs include developing a ground model both within and outside the site, identifying and characterising the properties of the geotechnical units, understanding the range of potential groundwater conditions, and determining the magnitude and orientation of in situ stresses.
4. The all-important engineering impact assessment
An engineering assessment may be required to prove compliance with relevant standards or guidelines through demonstrating that no adverse impacts on existing or proposed infrastructure are expected to arise from the proposed development. And, that any impacts from the operation of the existing or proposed underground infrastructure on the new development will be acceptable. The complexity of the assessment will depend on factors such as the depth of any associated excavations, the proximity to underground infrastructure, and the method of foundation support.
Completing an impact assessment typically includes:
- establishing relative proximity between the proposed development, the protected corridor and the impacted infrastructure
- developing the building design (and particularly its foundations and basements) to meet guidelines and requirements, which may involve some level of foundation redesign
- gaining agreement from the owner or operator of the underground asset, potentially with conditions of approval imposed that may require ongoing interaction with the developer before and during construction
- ensuring that conditions are met – through ongoing involvement of the owner or operator and their consultants with the developer and their consultants.
5. Technical obligations and drivers
During the engineering impact assessment phase, all the parties should understand the key technical obligations and drivers relevant to their development, including:
- Numerical modelling (analytical modelling of the current situation and the staged construction of the development, which encompasses critical elements of the underground infrastructure): This modelling should include, at a minimum, ground profiles and geotechnical parameters derived from site investigation, existing or planned structures, proposed building foundations, shoring systems for basement excavation and construction sequences.
- Ground movement and building impact assessment: This assesses the severity of potential ground movements and the associated actions on all modelled structural elements. The modelling results will need to be viewed against the protection guidelines or requirements, which may place restrictions on parameters such as ground movements, changes of stresses within rocks surrounding the infrastructure, forces on tunnel support or permanent structures.
- Instrumentation and monitoring plan: This plan establishes the means by which the realised impacts can be measured, reviewed and verified against predictions. It will typically need to provide for monitoring ground deformation, tunnel convergence, lining/rock mass stresses, crack width monitoring, vibration, reporting protocols and actions to be taken for specified trigger levels.
- Safe work method statements: Preparing Safe Work Method Statements (SWMS) is a fundamental necessity. The owner of the asset will need confidence that the development can be constructed safely without exposing the underground infrastructure to unacceptable risk. It is a typical requirement that a risk assessment report and safe work method statements are submitted by the developer to the approval authority prior to commencing any works on site.
- Noise/vibration assessments and stray current analyses: These important assessments need to be carefully prepared and should consider the potential impacts during both construction and operation of transport assets.
6. Seeing the view from above and below
To protect a city’s current and future transportation corridors as the built environment continues to expand, approval authorities will need trusted technical advisers who can provide practical advice underpinned by sound engineering.
Each new development is unique. That’s why technical advisers must treat each development on its own merit so there is less risk of imposing overly conservative or unnecessary generic requirements.
Consultants supporting developers to gain agreements and approvals for new works need to appreciate the concerns of asset owners and operators and address these in their technical advice and engineering assessments. This will streamline approvals and help all parties achieve a result that meets their expectations.
Protecting transport corridors and enabling new city development are not mutually exclusive, and can comfortably occur in parallel, when designs are based on sound analyses and engineering, and when all parties have a good understanding of each other’s needs.
To find out more, please contact Antoni Kuras and Jiping Pan.
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