FAQs

General Questions

Q: What is trenchless technology?
A: Trenchless technology refers to construction methods used to install new pipelines or rehabilitate existing underground services with minimal surface disruption. Traditionally pipelines have been built above the surface or laid in a slotted excavation (trench). Due to surface and now subsurface congestion, these construction methods are becoming increasingly more costly and challenging to undertake. Subsequently, trenchless pipe installation methods have been developed to install pipe from one location to another minimising the surface activities.

Q: What is trenchless design and engineering?
A: Due to the complex nature of pipe installation methods and operations, engineering models have been developed to estimate and minimise project and asset risks. Trenchless Engineering Australia offers a range of engineering products and services to streamline the design and construction of pipeline and conduit assets. Examples include assessment of frictional, bending and pressure loads on pipe during installation to minimise risk of product pipe damage, assessment of bending stresses, support reaction loads and pipe spans for temporary breakover design or geotechnical analysis of arching stresses and settlement modelling. Refer to the Products page for more information on how project risk can be assessed for projects.

Q: What are the main types of trenchless methods?

• Horizontal Directional Drilling (HDD)
• Pipe Bursting
• Microtunneling
• Auger Boring
• Cured-in-Place Pipe (CIPP)
• Sliplining

Q: When is trenchless construction preferred over open-cut methods?
A: When surface disruption must be minimised, such as in urban areas, under roads, rivers, or environmentally sensitive zones.

Q: What is drilling fluid?
A: Drilling fluid is a mix of water with thickening additives such as bentonite clay or polymers. Its primary uses include lubrication of pipe and downhole tooling, and to transport excavated cuttings. Trenchless methods utilise environmentally neutral drilling fluid products.

Q: What is a BHA?
A: Commonly referenced during HDD operations, the Bottom Hole Assembly (BHA) refers to the collection of downhole tooling on the end of a drill string. They are used to guide, drill, stabilise or condition a borehole. Examples of components include drill bits, steering tools, downhole motors, reamers, stabilisers, barrels or subs.

Technical & Design

Q: What soil conditions are suitable for trenchless methods?
A: There are a variety of trenchless methods to suit different ground conditions. For example, HDD works well in cohesive clay and sandy soils or rock, while microtunneling is better for mixed or unstable ground.

Q: How are the alignment and depth of a trenchless installation designed?
A: Alignment selection is largely dependent on construction corridor easements and an assessment of existing structures, services and features in the area. Depth of crossing is dependent on a variety of inputs including, gravity flow requirements, pipeline pressure capacity, and risk mitigation.

Q: How is the alignment and depth of a trenchless installation controlled during construction?
A: Through advanced guidance systems like gyroscopic steering, laser guidance, or wireline tracking.

Q: What are the diameter and length limitations of trenchless installations?
A: There is no short answer here 🙂 Contact us to discuss further as capacity varies by method, ground conditions and recommended bore length will decrease with increasing pipeline diameter. The HDD method enables the longest pipeline installations, current records are over 5km long.

Q: When should an enveloper pipe be utilised?
A: Enveloper pipes may be used to encase a carrier pipeline or a bundle of smaller pipes. They may be utilised if the carrier pipeline is not able to withstand externally applied loads, if the carrier pipe does not have the capacity to be installed via the trenchless method or to minimise the number of bores required. Note, while enveloper pipes are typically used to reduce risk, it is not recommended to use envelopers in all cases as the increase in bore diameter may increase other construction risks, as well as project cost and duration.

Q: When is borehole grouting required?
A: Often trenchless methods rely on an annular space between the borehole and the product pipe to minimise friction and install the pipe. After construction completion, surrounding geotechnical material may settle into this space or active groundwater may run along this path. Typically surface settlement is negligible, contact us for settlement analysis. For sensitive assets, grout may be pumped into the annular space to mitigate subsidence risks.

Cost & Risk

Q: Is trenchless more expensive than traditional excavation?
A: Upfront costs for trenchless methods may be higher, however savings are often realised through reduced remediation, faster timelines, and fewer disruptions. Project cost is largely dependent on the pipeline route. For cross-country pipelines with little road, service, or other crossings, trenching is very simple and cost-effective. For these large-scale projects, there are often smaller trenchless scopes for environmental areas such as waterways and steep escarpments. Pipelines in urban areas have to navigate significantly more infrastructure including existing services, structures, roads, and railways. In these instances, trenchless methods can be much more cost-effective, reducing schedule duration, minimising traffic control requirements as well as reducing project risk with increased separation to infrastructure.

Q: What are the common risks in trenchless projects?

• Inaccurate geotechnical data
• Ground settlement or heave
• Utility strikes
• Equipment failure
• Hydrofracture (fluid release)

Q: How are risks mitigated in trenchless construction?
A: Through thorough site investigations, proper method selection, real-time monitoring, and experienced operators. Contact Trenchless Engineering for assistance with risk optioneering and Safety in Design workshops.

Permitting & Environment

Q: Are special permits required for trenchless work?
A: Yes, especially for works under waterways, railways or roads. Permits may involve environmental, traffic, and utility coordination.

Q: Is trenchless technology environmentally friendly?
A: Yes, reduced excavation volume means less soil displacement, lower emissions, and minimal impact on surface ecosystems.

Q: The pipeline crosses through ASS areas, is this an issue?
A: Acid Sulphate Soils have a low pH value and may be classified as contaminated waste. Once excavated, ASS needs to be contained and disposed of in line with environmental regulations. The implementation of trenchless construction methods can assist crossing through ASS zones, or any other contaminated areas, as the amount of excavated material and therefore quantity of contaminated waste is reduced. Additionally, trenchless methods such as HDD using treated drilling fluid can neutralise the acidic pH of the soil. With appropriate EPA testing, the excavated material may be reclassified as clean fill (granted there are no other contaminants present).