When in PRE-PLANNING stages, it’s important to remember:
- Each and every HDD project should be seen as site specific
- Knowledge is key, but sometimes a little bit of knowledge is dangerous
- The project should always be seen as a power, water, communication etc, project. To the client the project is an asset installation; it is not an HDD project though they must both go hand-in-hand.
- HDD is the method for installing the asset, but the methodology must still conform to the client’s requirements, and transition to existing networks as well as other existing asset and infrastructure owner requirements
For HDD projects, the most common problems and issues encountered generally are:
- Utility strikes
- Unachievable bore designs
- Unachievable bore construction
- Unacceptable bore construction
- Failed bore (borehole collapse)
- Failed or unacceptable product pipe installation
- Unacceptable costing variations or incorrect pricing (both budget and construction)
- Extended construction time schedule
- Frac-outs/ground heaving and other environmental issues
- Inaccurate bore location
- Slow “÷in principle’ approval acceptance/process for the crossing of other existing assets.
It is usually not one single area where most problems and issues can occur, but over a range of different sections within a HDD project.
These can be characterised as:
1. Site investigation
4. Technology limitations
5. Product pipe
6. Tender documentation
7. Tender review process
8. Contractor’s ability
9. Monitoring of construction process
A number of issues can arise from improper site investigation.
A limited survey – or no survey at all – can lead to incorrect information.
Additionally, missing information, such as river bed contours can have far reaching implications during the drilling process.
Geotechnical information gathering at this stage of the project is highly important.
Issues can arise from limited or no geotechnical, which includes: inconclusive investigation depth, inconclusive information, and
not investigated as per required trenchless method.
Failure to conduct a thorough investigation of existing utilities in the area could include no DBYD review, no potholing to confirm utility location and no data for incorporating into design.
Issues in design arise from:
- An inexperienced trenchless designer
- Incorrect or poor trenchless method selection
- Little to no knowledge of trenchless limitations
- Unrealistic targets or parameters (unachievable and unnecessary)
- Unsafe and impractical clearances between existing utilities and proposed borehole
- Incorrect or no understanding of required trenchless parameters, such as bend radii, bore length, entry and exit angles, safe bore depths, borehole size.
If a bore is required to be constructed under or within a corridor owned by another asset owner, such as road or rail, then an approval for construction may be required.
This will be given by the existing asset owner to the new asset owner once it has been proven that the proposed bore will not damage or pose a risk to the existing asset.
This process can be frustrating for many who go through the process as many existing asset owners have their own requirements and specifications that need to be adhered to.
The selected technology can cause issues if the client’s or designer’s knowledge on the trenchless equipment and its abilities are limited.
- Insufficient or impractical site set up area requirement
- Impractical access for required trenchless equipment
- Impractical trenchless capability within expected ground conditions
- Unsafe trenchless undertakings to achieve client requirements
- Impractical or extremely difficult requirements for tracking or steering of downhole tooling.
It’s important that the product pipe selected is compatible with the trenchless installation method and downhole requirements.
Limitation of chosen product pipe includes its achievable bend radii, axial forces and critical buckling pressures.
When deciding on product pipe, it’s important to consider installation/downhole requirements and limitations, pipe availability and on-site layout achievability.
The onus is on project owners to ensure tender documentation includes sufficient detail and is realistic in what it sets out for the contractor.
Problems with tender documentation which may arise include limited details for technical requirements, limited or incorrect details of required trenchless equipment and its abilities, and unrealistic parameters and requirements.
Issues may arise from limited requests for contactor information before, during or after the construction process, this could include the bore plan, methodology, bore logs, testing procedures, equipment to be incorporated and personnel to be used as well as construction time frame.
Tender Review Process
It’s important those reviewing the tender have a thorough trenchless knowledge.
Issues the reviewer may encounter include:
- Inconsistency of submitted pricing
- Risk of variations
- Risk of substantial construction time increase
- Risk of project not being constructed as per client requirements or failing
- No confirmation of submitted equipment
- Wide variety of inclusions and exclusions.
Ensuring the contractor you select is competent and suitable for undertaking your required works is vital for the success of the project.
Unfortunately in this day and age some people will say whatever it takes to win a project.
It’s up to the client to request contractor’s information regarding previous projects undertaken, available equipment, personnel experience and even a methodology and bore plan to show they have an understanding of the works required.
Monitoring of construction process
During all phases of construction from mobilisation to demobilisation, it’s important that independent monitoring of the contractor and their processes are undertaken.
This monitoring should be undertaken by personnel with a good deal of experience within the chosen trenchless method chosen to ensure that if any issues do arise, they are quickly noted, brought to the clients attention and handled efficiently, practically and professionally.
Solutions and risk minimisation
The below checklist should be referred to before undertaking any trenchless works.
- Undertake proper site investigation and understand it’s relevance to the trenchless method and design chosen
- Site visit, geotechnical, survey and existing utilities
- Select the most appropriate trenchless method
- Compile an achievable and practical bore design
- Compile detailed tender documentation
- Ensure all risks are understood and known by both client and contractor
- Review all contractors submissions for experience, available equipment, personnel etc
- Request a bore plan and methodology from the contractor before any works are undertaken
- Ensure all approvals are obtained before the contractor is on-site
- Ensure the contractor’s submitted equipment is being used on-site
- Review all contractor’s on-site documentation including safety, environmental, existing utility plans, SWMS etc
- Monitoring of the works with knowledge of proposed bore plan, equipment, methodology and work practices
- Have an independent authority to confirm any re-design, problems or issues
- Have achievable targets or hold points the contractor has to achieve before continuing
- Never assume.